The Majestic Clockwork
Theory without facts is fantasy, but facts without theory is chaos.
~ Charles Otis Whitman
Welcome to the blog series Borrowed Time!
Most living things are small and most living things don’t live very long. Handily, these two facts are predicted by the laws of physics. The universe is hurtling towards a state of complete disorder. Politics in my lifetime has provided nothing to doubt this relatively recent scientific discovery. Entropy is inescapable, but in this blog series we will examine how biological organisms temporarily defy this general trend. We will discuss the role physical laws have played in the evolution of life on Earth, and we will explore the natural world through an Einsteinian lens.
Every plant, every animal, every microbe; we are all living on borrowed time.
Death comes to all. But great achievements build a monument which shall endure until the sun grows cold.
~ George Fabricius
Here Be Dragons
The metaphors we use profoundly affect the way we think. Metaphors shape our perception of reality. Predominantly used as a tool to understand complex ideas, they provide a frame of reference that is more familiar, and easier for our brains to grasp. The world’s a stage, God is the good shepherd, and even these words that you read now are but crumbs that fall down from the feast of the mind. Metaphors are a very high form of abstraction that aids our comprehension of the world around us. As we learn more about our planet, we update our metaphors, to hopefully provide a better reflection of reality. But it is important to remember they will never be anything more than a reflection. It is important to always be cognizant of the distinction between what is abstraction and what is real.
This abstracting process is by no means limited to metaphors. When we partition the myriad colors of the rainbow into seven levels, we are abstracting. In reality the seven categories do not exist; the words “red” and “yellow” are merely squiggles on a page that we ascribe meaning to, a way to categorize, to simplify the constant flux and infinite variety of nature. In reality, the beauty of the rainbow is beyond words. Maps too, follow the same principle. Maps are squiggles on a page designed to characterize and describe our geographic surroundings. When we draw maps, we are engaging in abstraction. The distinction between map and reality becomes easier to see with time; when you study a map from centuries past, it is impossible not to be drawn to the missing continents and the crude coastlines. But there will be a time when the maps of today are viewed with similar derision. It cannot be helped; the abstract world by its very nature is limited, subjective, and often wrong.
Interestingly however, despite the inherent deficiencies of our maps and metaphors, abstraction is the main conduit by which our species advances. Just as imperfect maps can still be used to navigate the globe, imperfect metaphors can still be used to develop scientific knowledge. Not only do clunky metaphors allow scientists to readily communicate with each other about the nature of reality, but also much is learned from scrutinizing aspects of the metaphor that do not line up with what is observed in the real world. In the first half of the 20th century physicists argued about whether the appropriate metaphor to describe light was a wave or a particle, before reluctantly coming to the realization that the correct answer was both (or neither, if you are a glass half empty kind of person). Far from being a fruitless semantic discussion, these competing metaphors were instrumental in the development of quantum mechanics and revolutionizing our understanding of atomic matter. Here I argue that we are long overdue for a similar discussion within evolutionary biology, in order to overhaul our current perception of life on earth.
Eternity in an Hour
The universe is colossal. Fantastically old at fourteen billion years, and 93 billion light-years across, spacetime is vast. At this scale, the history of our planet pales into insignificance. Living things come and go in the blinking of an eye. The rise and fall of species barely register against the backdrop of galaxies colliding and solar systems forming. Entire lineages of organisms emerge, evolve, and are extinguished in a flash. In the game of life, genotypes are the only things that achieve anything close to immortality; as generations turn over en masse, successful strands of genetic code march on through time. But even genes carry a modest expiration date, a rather paltry longevity when considering the cosmos in its entirety. Thus, for the human brain to even begin to comprehend the universe and all its grandeur, we must first condense its history to a timescale more familiar.
The cosmic calendar is a metaphor for the history of the universe that shrinks and arranges all of time right up to the present day into a single year. Thus, the big bang kicks things off in the first seconds of January 1st as the New Year’s bells are still ringing out, and as you read these words we are approaching midnight of December 31st. Each month of the cosmic calendar lasts over a billion years, each day is approximately 40 million years long. On this scale, in this abstract world, four centuries fly by with each passing second. As gases from the early universe began to coalesce under their own weight, the first stars ignited towards the end of January. Our own galaxy, the milky way, formed in mid-March. As this is a biological essay we must regrettably brush over the entire summer of the comic calendar, for whilst there were many interesting developments taking place throughout the cosmos, life, as far as we know, did not emerge until well into autumn.
The planet earth, the only place from which we know that life exists, did not form until mid-September. Three quarters of the universe has already been and gone, yet the big rock you are currently sitting on is only now coming into existence. Somewhat surprisingly, it did not take life long to get started once the dust and debris had settled, and the planet had solidified. Indeed, the tree of life began to sprout within a fortnight, somewhere around September 25th on the cosmic calendar. Although our record of early biology is understandably scant, we know that life spent the next few months perfecting the single-celled organism. The majority of biodiversity on earth is microbial, and all of life’s fundamental biological processes – photosynthesis, homeostasis, sexual reproduction – were stumbled upon by these invisible pioneers. Multicellular life forms took 80 days to evolve from single-celled organisms, roughly three billion years in real time. On the cosmic calendar it is already December, and only now do we start to encounter life forms visible to the naked eye. A door to a hitherto unimagined world of possibilities and innovation has opened. As we know, life gladly stepped through that door.
Heaven in a Wild Flower
Our primary metaphor to describe the history of life on earth is a tree. The tree of life is ancient; its bark gnarled and strengthened from years of fighting with the elements, its crown a seemingly unending tangle, with branches stretching into every nook and cranny this planet has to offer. Although the metaphor is intuitive, stemming as it does from the familiar family pedigrees, under scrutiny it is perhaps not so apt. For one, the tree metaphor does nothing to capture the diversity of living things. A tree, after all, is a single organism. It is too uniform, both in growth and structure, to provide an adequate representation of evolution in all its glory. Moreover, most of the tree of life is dead. Those organisms that make up the trunk and crown of our metaphor are long since extinct. It is only the tips of the branches that represent species still alive and kicking. But this is not how a real tree works; the roots are as much alive as the leaves, the pith contemporaneous with the bark. At a certain point we must concede that the metaphor does more to obfuscate than enlighten us as we attempt to visualize the history of living things. A growing contingent in evolutionary biology therefore, is advocating for life to be thought of not as a tree, but as an immense coral reef.
Although only gaining significant popularity in the last few decades, the coral of life metaphor was first proposed by Charles Darwin. Given that he spent the formative years of his career scampering about rock pools in search of barnacles, it is perhaps not surprising that he opted for a maritime metaphor. There are several important improvements that the coral metaphor has over the tree. The way that different corals jostle for space, fighting over territory and resources, is much more comparable to the way real species interact. Neighboring corals compete ferociously with one another until more often than not, one gains the upper hand and consumes its rival. In contrast, survival of the fittest is not readily captured by branches on a tree. Coral reefs also do a better job of conveying the snowball effect that life often exhibits. As the reef grows, opportunities open up for a whole slew of new organisms to join the community, building off of each other. With time, the reef becomes its own ecosystem, master of its own destiny. The same is true for the history of life on earth – diversity begets diversity, as the saying goes. Whilst a tree can shelter birds and provide suitable moorings for moss and lichen, these community aspects are typically not included in our botanical metaphor.
Perhaps the most important improvement the coral of life has over the tree of life is that only the visible part of a coral reef is still alive. The core of a coral is dead – a vast boneyard, layers upon layers of generations past, reflecting previous iterations of the reef now smothered by their contemporaries. Evolution precedes in this fashion. The vast majority of species have gone extinct. Of the species that are still around, the vast majority of individuals have died. A fleeting existence is the rule. It is difficult to comprehend the taxa that have been lost to time. Indeed, we only have records for a minuscule fraction of those that have already succumbed. Species that only appear for a brief moment on the cosmic calendar are likely to leave no trace. In all probability, a species must last several million years for us to even know about it. Species that survive for days or even weeks on the cosmic calendar are exceptional – organisms that defy the odds, somehow enduring eons of dramatic environmental change without breaking stride. Some of those miraculous species are still alive today, and we call them living fossils.
Frozen in Time
Most living fossils are large and most living fossils are long-lived. These two things are not unrelated. The link between body size and longevity is well established. An elephant lives longer than an elephant shrew. A blue whale lives longer than a bluebottle. Purely from a statistical standpoint, long-lived species are more likely to appear frozen in time – a century equates to 3,000 generations of Drosophila fruit flies, but only 40 generations of Galapagos tortoise. Small animals with short lifespans typically favor the strategy of rapid diversification. By diversifying into many different forms, the group as a whole fares a better chance of persisting long term. Insects are perhaps the best example of this; radiating into thousands of slightly different species as a way to hedge their bets in light of future uncertainty. In this way, insects are collectively able to achieve a pseudo-immortality – even if environmental conditions change drastically, insects as a group will persist, indeed several will likely flourish. Living fossils do not adopt this strategy. In most instances living fossils are going it alone, and instead striving for a truer form of immortality.
Most living fossils live in the ocean. Water is far more stable than land. Terrestrial creatures must constantly be taking measures to prevent themselves from drying out or freezing in the harsh unpredictable environments they are subjected to. This is not the kind of place to vie for immortality. Instead, the deep sea, where environmental change is less dramatic, more predictable, and occurs over longer timescales, is where to search for ancient relics. Pretty much all sharks are living fossils; these ancient mariners have been reigning supreme since before the dinosaurs. Ocean depths in particular are home to a plethora of these apex predators, unchanged for millennia, perfectly adapted to silently cruise the blackness in search of unsuspecting prey. Whether gulpers or goblins, frilled or six-gilled, what worked for sharks 100 million years ago works for sharks today. Accompanying sharks in these murky waters are horseshoe crabs, vampire squid, Nautilus, and perhaps the archetypal living fossil, the coelacanth. The stability of this environment allows nature to find strategies that work and stick with them. Many scientists now believe that life originated at the bottom of the ocean; the same stability that led to the emergence of living fossils is thought to have been instrumental in the genesis of living processes – the very sprouting of the tree of life.
On land living fossils are more the exception than the rule. Owing to the vagaries of the seasons the predominant strategy of terrestrial organisms is one of adaptability. In most instances the inherent unpredictability and dynamism of life out of water prohibits the slow and steady approach. On land, get-rich-quick schemes are in abundance. Insects again are the best example. Exceptional circumstances are required for living fossils to emerge on land, and it is perhaps only oceanic islands that provide those circumstances. Owing to their extreme isolation, islands are cut off and therefore largely immune from changes taking place in the wider world. Tuataras, lemurs, and giant tortoises could all be considered living fossils. Their island homes have acted like refuges, whereby tuataras were never replaced by modern lizards, lemurs were not out-competed by other primates, and giant tortoises did not have to share their food with grazing ungulates. Today however, even the most remote archipelagos around the world are at risk from unwanted visitors and dramatic upheavals. Adapting to the apparent stability of island life is risky business in the modern world. Most extinctions in the last two centuries have occurred on islands.
You Don’t Miss Your Water
The term ‘living fossil’ rings of immortality, species that somehow cheat death, species that manage to avoid the ravages of time. Sharks nonchalantly saw the rise and fall of the dinosaurs; horseshoe crabs hardly skipped a beat as the rest of the world was ravaged by four mass extinctions. But that was then, and this is now. For these timeless creatures, time may be up. Living fossils are buckling under the onslaught of humanity. Soon living fossils may simply be regular old fossils. Sharks have declined by 90% in the last century. Horseshoe crabs were nearly wiped out as a result of overharvest for the development of vaccines. On land things fare no better. Tuataras lie on the verge of extinction following the introduction of rats and cats to New Zealand’s offshore islands. Lemurs and giant tortoises have largely been eaten off the map. Unsurprisingly, the evolutionary strategies of long-lived giants only work if the adults do indeed live a long time. Before humans rose to prominence, the ranks of chondrichthyans and chelonians were practically invincible. In the Anthropocene, nothing is invincible.
The coral of life is vast; a four-billion-year-old living city that will outlive us all. On the timescale of the cosmic calendar, entire lineages of plants and animals emerge and disappear in a matter of minutes. Extinction is a natural, integral component of life’s great story, and despite humanity’s best efforts, life will persist long after we’re gone. We do not hold the power to extinguish biodiversity, but we certainly have the power to impoverish it. Most wetlands have been drained, most forests cleared. Our impact on the reef is acidic – our actions corrode. And in time the floor on our own standard of living is also eaten away. Without biodiversity we do not have clean drinking water, food, medicine, or shelter. It is the world’s poor that will suffer most from climate change. It is the world’s poor that will suffer most from environmental destruction. It is the world’s poor that will suffer most when the food and water run out. Conservation therefore is ultimately a self-centered vocation; we are not trying to save the planet, we are trying to save ourselves. We have been foolish to leave conservation efforts to the eleventh hour. We mustn’t delay any longer.
As December rolls through on the cosmic calendar, the timeline begins to become almost frantic, with seminal events occurring on a daily basis. Fish first appeared in the oceans on December 19th. Plants colonized the land on the 20th, insects following shortly after on the 21st, and amphibians around noon on the 22nd. Reptiles first appear on December 23rd. The most famous group of extinct reptiles, the dinosaurs, sprung up on Christmas Day – what a treat! By now you may have realized that on the cosmic calendar, all of human history is relegated to the evening of December 31st. We have barely registered on the universe’s great tapestry of events, the great chain of being. From the dawn of our species, barely a minute has elapsed. The pyramids of Giza were built only 12 seconds ago. The printing press was invented in the last second. Whether human beings will register even an hour on the cosmic calendar remains unclear, but all things must come to an end.
Life in the Fast Lane
Time is a sort of river of passing events, and strong is its current; no sooner is a thing brought to sight than it is swept by and another takes its place.
~ Marcus Aurelius
“But I don’t want to go down there” the boy pleaded. “You’ll do as you’re bloody well told” the elderly gentleman barked in response. At 6’5’’, and with a mustache that sparrows could nest in, Johnathon’s father cut an imposing figure; this was an argument John was not going to win. For as long as he could remember, his father had always been obsessed with noxious gases. By this point in his life, Haldane Sr. had already invented respirators and oxygen tents to combat chemical warfare in Europe, and decompression chambers to facilitate deep-sea diving in the Atlantic. Now he was turning his attention to the mines of South Yorkshire. With a cage of yellow birds in hand, the eccentric Englishman descends into the gloom. His son reluctantly follows.
The Light that Burns Twice as Bright
The vast majority of life on Earth occupies the fast lane. At the level of the individual organism, it seems there is often neither a second to spare nor a moment to lose. Most microscopic organisms, the dominant life-form on Earth, exist for a fraction of a moment. Generations pass in the blinking of an eye. Bacterial colonies that resemble bustling cities emerge and are extinguished in a matter of hours. Microbial empires rise and fall with the sun. The majority of plants and animals also operate at breakneck speed, completing their life-cycles in a matter of weeks or months. Following emergence from shallow mountain streams, the lifespan of female mayflies averages five minutes; males of the species however, may be fortunate enough to survive for a whopping two days. In sub-Saharan Africa, turquoise killifish reach sexual maturity within a fortnight of being born. There is good reason for such haste; these inch-long fish must grow, find a mate, and reproduce before the pools they inhabit evaporate in the equatorial heat. To dawdle would spell disaster. To dilly-dally would beget certain doom. For many creatures on this planet, to live fast and die-young is the only option available to them.
The tendency for living things to exhibit a fast pace of life is driven by the same forces that shape all aspects of biodiversity. Just as the cuttlefish’s eye or the sparrow’s wing are crafted by millions of years of random variation, survival of the fittest, and inheritance, so too the internal clocks of species are set by generations of Darwinian trial and improvement. Species are in an eternal arm’s race with themselves and each other. There is no respite from competition and the purging effects of natural selection. As the Red Queen remarked to Alice: “Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!”. In this cutthroat competition, speed typically wins out. Ecological niche theory includes a ‘first-come first-serve’ principle - establishing yourself before your rivals do provides a tremendous advantage and can decide the outcome of competitive battles. In addition, a fast pace of life is better at dealing with the inherently unpredictable and constantly changing world we find ourselves in. The present provides the only certainty. Rarely is it worth sacrificing what you can guarantee in the here and now for a potential payout further down the road. For species that gamble on tomorrow, the odds are seldom in their favor. Simply put, most things operate in the fast lane because that’s what works.
Of course, as Einstein demonstrated, time is relative, such that species in the fast lane do not feel as frantic as they appear to human eyes. The watches of the mayfly and the killifish tick much slower than ours, and thus a day, or even an hour, feels to them like ample time to live a long and fulfilling life. The reason why most animals appear to human eyes to be operating at breakneck speed is because we are far bigger than them. Being big has its perks. Owing to our size, human beings can reach ages unthinkable to the majority of animals, and even without the aid of modern medicine we thus enjoy a relatively leisurely existence. The strong relationship between body size and longevity is largely explained by the fact that fewer things can eat you when you are big. There are reproductive payoffs too. Living longer allows organisms to experience more reproductive opportunities in their lifetime and perhaps invest more in those reproductive bouts. An 80-pound Atlantic cod for example, can produce nine million eggs every year for two decades. One would think that natural selection should always favor these types of long-lived, ultra-fecund species, but their relative paucity suggests that such a strategy is easier said than done.
Reaching a large size in order to live longer is no picnic. Trouble finding enough food, elevated space requirements, and the added risk of delaying maturity in favor of rapid growth all act in concert to encourage most animals to stay small. Given the considerable challenges associated with reaching large sizes, it is not surprising that numerous animals have devised strategies to enjoy the benefits of being big without actually being big. Poisonous dart frogs and venomous serpents both live a long time despite their small stature, in part because they are avoided by many a would-be predator. Camouflage and spines operate in the same way - allowing relatively small things to not be eaten by the menagerie of predators that are certainly big enough to eat them. Other species boost their survival to that of larger beings by banding together. There is safety, and an opportunity for serenity, in numbers.
If competition is the catalyst for accelerating the pace of life, cooperation is the catalyst for slowing it down. From eusocial insects to colonial jellyfish, cooperation has allowed species to defy the march of time; whilst the lifespan of any one individual within the colony remains short, the superorganism that constitutes the beehive or Portuguese man o’ war persists far longer. At a more fundamental level, the Eukaryotic cells that act as the building blocks for all plants and animals are thought to have originated as a form of cooperation, whereby internal structures such as mitochondria and chloroplasts were originally free-living microbes that banded together to form a mutually beneficial relationship, effectively becoming codependent roommates. This fundamental partnership eventually led to the evolution of multicellular organisms. Any multicellular organism therefore should be regarded as a colony of colonies. The average lifespan of the mitochondria in your cells is 100 days; the average lifespan of the cells in your body is 7 years. In the western world one of these bodies can persist for approximately 75 years. In nature, it appears time shared is time doubled.
The long-distance seasonal travels of birds are some of the most spectacular and familiar biological phenomena on the planet. Animal migration is in essence an attempt to achieve more in a shorter amount of time. Einstein demonstrated that time and space were one and the same. Seasonal environments provide a nice example of this - if you want to experience the cold you can either move closer to the poles or wait until winter, i.e. travel across space or through time. Migratory species exploit this relationship; by avoiding the vagaries of the seasons they can effectively keep their foot on the gas all year round. Birds that travel to summer breeding grounds in the high arctic benefit from the largely untapped resources at high latitudes without having to endure the seemingly inhospitable conditions throughout the rest of the year. This allows migratory birds to remain relatively small yet still ‘live it large’ so to speak. Permanent residents of the poles in contrast, either must hibernate to survive the harsh winters, or become massive to more effectively regulate their body temperature.
Although migration has manifold benefits, it is physically demanding. Most animals would struggle to travel from Cuba to Canada unaided. As a rule bigger animals can move further than smaller ones. Even so, the blue wildebeest, weighing in at a third of a ton, only manages to haul itself across two African nations as it tracks seasonal rains across the Serengeti. Most living things are not as big as wildebeest. For small animals to fully take advantage of space, they must get creative. Birds and insects can make use of multiple habitats regardless of how far apart they are because birds and insects have wings. With the evolution of the wing, body size no longer exerted a meaningful limit on dispersal distance. Wings remove barriers - vast oceans and impassable mountain ranges suddenly become passable to all that possess them. Bats are tiny for the most part, but have colonized nearly every archipelago on the planet. Insects outnumber all other animals put together, and they occupy every corner of the globe. Flight is chiefly responsible for their success, and wings are often the defining characteristics for the myriad insect groups: Diptera, the fruit flies, meaning two wings; Coleoptera, the beetles, meaning shield wings; Lepidoptera, the moths and butterflies, meaning scaly wings. Most of these insects do not live that long, because their ability to cover large distances relatively efficiently allows them to get everything done in a shorter space of time.
There are many birds that do not migrate. And many wingless creatures that do. The choice between a sedentary and a nomadic lifestyle is more complicated than simply have the prerequisite tools, and the transition from one to the other is likely serendipitous. Take the intriguing case of the cattle egret. Originally restricted to central Africa, cattle egrets now occupy every continent on the planet barring Antarctica. Facilitated by agricultural expansion in the 20th century, in less than 50 years cattle egrets have conquered Australia and Europe and now occupy every US state, outnumbering all other egrets and herons in North America. Most cattle egrets from their African homeland do not migrate. Shortly after arriving in Australia however, these same birds developed a brand new migration route, flying south to Tasmania every summer to avoid the sweltering heat of tropical Queensland. American flocks have evolved similar habits, but instead fly north to Canada, shadowing native heron flocks along their long-established migration routes. Interestingly, birds residing on the Indian subcontinent have already learnt to tie their movements to the monsoon rains, suggesting that this behavior is flexible not just in terms of the direction of travel but also in terms of the environmental cues that are used to trigger migration. Again, all of this variety has emerged in the last century.
Human beings used to migrate. Some still do. But most, take up permanent residence at one fixed location. This may be logical if that chosen spot is somewhere in the tropics, where primates first originated and where conditions are genial year-round, but such a strategy makes considerably less sense in the desert southwest of the United States say, or Canada’s frozen north. For a species that does not hibernate, the energy consumption required to make such places even remotely habitable is absurd. The folly of humanity’s need to permanently occupy every corner of the globe is readily apparent. The western desire to live a life of constant comfort and luxury does not square well with the harsh environments that we have expanded into. We are attempting to live life in the slow lane in situations where it simply isn’t appropriate, and if we do not change our ways, soon we will be left behind. When the fossil fuels run out and the wars for freshwater begin, a reversion to nomadism may be on the cards for humankind. We cannot defy the elements forever; the march of time is inevitable and all consuming. Entropy continues to flow despite our best efforts. We cannot swim against the tide for much longer.
“Pay attention John, this is important” the boy’s father grumbled impatiently. “Besides tunnel collapse, the biggest hazard in mining operations is the build-up of toxic gases. In these confined spaces methane explosions are common; every swing of a pick-axe risks creating a fatal spark - that’s all it takes. There’s a lot of hydrogen sulphide down here too. You smell those rotten eggs? Enough of that stuff and you’ll be unconscious in seconds. But the real one you want to worry about is carbon monoxide. Carbon monoxide is odorless, so impossible to detect, but can be deadly. It slowly replaces the oxygen in your blood and you suffocate. This is where the canaries come in. These small birds will suffocate much quicker than you or I, and thus they provide an early warning system for men to get out of the mine shaft. Do you understand?” “I think so” replied the boy, “although I don’t understand why you had to bring me all the way down here.”
Life in the Slow Lane
For a moment, nothing happened. Then, after a second or so, nothing continued to happen.
~ Douglas Adams
Of Moose and Men
The sun is setting. I carry my cup of tea, the last of the day, out onto the back porch. Reclining in a chair, I take in my surroundings. Mountain skies are spellbinding. As dusk approaches, azure blue turns to a breath-taking blend of burnt umber, rouge, lilac, and crimson. Only Turner has come close to capturing the color of nature, in all its subtlety, in all its striking beauty. By six o’clock, the sun’s rays are sepia-toned and fractured as they pass through a tangle of tree branches. Long shadows cross the lawn, on which several deer are sat. They have all made sure to pick spots that will remain illuminated until the last possible moment. Bathing in the gentle warmth of the evening air, their fur glistens and their eyelids droop. They appear as content as I. At last, the sun finally disappears below the horizon. There is a guitar leaning against the side of the house, but in my captivated state it remains unplayed; another time perhaps. It can wait. Everything can wait.
Many Rivers to Cross
Life in the slow lane is a gamble. Species will only refrain from operating at breakneck pace if the rewards are great enough. Species that dare to take their foot off the gas live long enough to experience the vagaries of the seasons; they are forced to endure great change. The longer you live, the more likely it is you will experience lean times, and to deal with such hardship is not a trivial task. What’s more, animals with a protracted life-cycle run the risk of producing no offspring if they die before reaching sexual maturity. Experiments on guppies have shown that when predators are introduced to the streams they inhabit, the fish will mature earlier. “Get some offspring out quick!” is the overarching message of selection. In many amphibians, high predation pressures experienced during the larval stage can trigger early metamorphosis; the elevated risk of the aquatic habitat acts to speed up the transition to land. Similarly, individuals can recognize when the pond they are in is about to dry up, and the possibility of imminent death will translate to rapid development of the tadpoles. Frogs that emerge prematurely are often small, not having as much time as they otherwise would have to gorge themselves on the pond’s bountiful algae supply, but they are alive, and that is what counts. An individual’s pace of life therefore, is not a choice per se, but a consequence of the environment it finds itself in.
If an animal exists in a relatively safe, bountiful environment, the animal will grow big and live a long time. When predators were removed from the experimental guppy populations, females deferred maturation in favor of a prolonged growing period. Bigger females produced more eggs, and thus the benefits of delaying outweighed the risks. This idyllic, predator-free environment is altogether unlikely in a natural setting however; it is after all, a jungle out there. In most instances, the need to find food forces animals into risky situations, and the different ways species’ balance this risk-reward trade-off is what generates much of the diversity that we see in the natural world. Creatures that spend most of their time hiding from the elements and/or would-be predators will not grow very big. Plethodontid salamanders in the Eastern US spend 99% of their lives safe underground, only emerging on a handful of days each year when the risk of foraging is minimal. These salamanders weigh only five grams but can live for three decades. At the opposite end of the spectrum, creatures that are willing to venture into dangerous places to exploit more plentiful resources grow much bigger but will typically not live as long. The exception would come if somehow you can grow so fast and to such a size that you outgrow your natural predators. Big things live longer because fewer things can eat them, but getting there is the challenge. The offspring of big animals must throw caution to the wind and eat like there’s no tomorrow if they are to ever attain the size of their parents. Typically for this risky strategy to succeed, big animals either lay huge clutches of eggs, with the assumption that most will not make it to adulthood, or invest in substantial parental care to improve the survival odds of their young. Only once you are grown can you afford to take your foot off the gas.
Food for Thought
With estimates pushing 400 years, the Greenland shark is by far the longest-lived vertebrate, providing some insight into life in the slow lane. Although not the largest shark species, these geriatric giants are just shy of five meters long and can weigh up to half a ton. As their name suggests, they are found at high latitudes in the northern hemisphere, and live at depths of 7,000 feet. Something about this environment allows Greenland sharks to take their foot off the gas and live a long healthy life, but what? Well firstly, in contrast to the Trinidadian streams occupied by guppies, or the breeding wetlands of frogs and salamanders, the ocean is relatively stable. When one can predict future conditions with relative confidence, a slower pace of life is less risky. Another potential feature of the Greenland shark’s environment that facilitates long lifespans is the lack of UV exposure. Ultraviolet radiation causes genetic mutations, any one of which could develop into a life threatening cancer, but the creatures of the deep do not have to worry about melanomas as we do. Lastly, and perhaps most importantly, the lack of sunlight means that the water at the bottom of the ocean is very cold. Temperature controls the rate of fundamental biological processes operating in every cell, and thus temperature exerts a powerful influence on the pace of life. Metabolic processes are slower at lower temperatures, and more efficient (think about fuel economy at 30mph vs 70mph). Hence in the frigid polar waters of the northern hemisphere, Greenland sharks are converting every drop of food into usable energy. Every morsel they ingest can be directed toward growth, cell maintenance and prolonging life. As they cruise through the gloom not a single calorie is wasted, and every calorie is used to its full potential.
On land you also tend to find older animals in colder climates. Polar bears, moose, and walruses all live longer than their cousins at lower latitudes. But none of these animals live as long as Greenland sharks, and the reason once again relates to temperature and metabolism. Warm-blooded animals do not live as long as cold-blooded animals. And polar bears, moose, and walruses are all warm-blooded. Regulating your body temperature is good if you want to remain active year-round at the poles, but it comes at a price. The relatively large sizes of these arctic mammals may lead you to believe that they occupy the slow lane, but their warm-bloodedness means they are effectively burning the candle at both ends. A 500lb moose does not live appreciably longer than a 5g salamander. A fully grown moose has few natural predators, but most of the energy it consumes does not go toward living longer - it is simply lost as heat. Cold-blooded animals can essentially shut down their bodies in between meals to conserve energy, and go months without food - owing to the need to stay warm, no bird or mammal can afford to eat so infrequently. This is especially true for small warm-blooded creatures, which have a much harder time regulating their temperature. This fact alone explains why there are penguins but not parakeets in Antarctica; why there are seals but not shrews at the north pole. Their relative inefficiency, combined with regular forays into risky environments in the constant quest for food, make it so that warm-blooded animal must grow to the size of an elephant or a whale if they are to enjoy a relaxed pace of life.
Desert Island Risks
Picture it. A tropical paradise, blonde sands calmly caressed by the cool blue, a gentle ocean breeze brings salt and seaweed to the nostrils, and unseen birds bring a sweet melodious symphony to the ear.
But there is trouble in paradise.
Islands may seem distant and immaterial, but these microcosms are home to some of the most precious wildlife on Earth. There are thousands of islands, each one a world in miniature. Just because life on islands have so little room to move, does in no way mean that life on islands is any less complex, intricate, and unfathomable than life on the mainland. Indeed, island inhabitants face unique pressures that provide opportunities for life to experiment and evolve, generating weird and wonderful, almost mythical creatures. Importantly for this discussion, island life can afford to take its foot off the gas. Birds on oceanic islands enjoy such a leisurely existence, many forget how to fly. The scarcity of trees and lack of predators encourages them to nest on the ground, and wings become somewhat redundant. What’s more, the ability to fly may even be a disadvantage in these remote places; it is unlikely that avian castaways will stumble upon better real estate in the surrounding area, and they may not be able to navigate back to their present locale if they up sticks and leave. Thus there is often a strong pressure to stay put. The seeds of island plants typically get heavier for the same reason; if they floated on the breeze they would simply be swept out to sea. Their inherent isolation is what makes each island unique. It is this same isolation however, that makes islands so inherently vulnerable.
Islands are the geographical equivalent of immune systems that have yet to be exposed to infection. They lack the acquired defenses to combat illness, and hence the fallout from exposure to novel diseases is often fatal. In the 21st century islands are sick, and we are to blame. However, human beings are not the disease in this analogy. Like mosquitoes, acting unknowingly as a vector for the real nasties, malaria, dengue, zika, we are in turn merely vectors for the real pathogens: cats and rats. Half of all known extinctions in human history have occurred on islands. Ninety percent of all bird extinctions have occurred on islands. Rats and cats are responsible for most of these. With so many islanders succumbing to rather mundane predators, it begs the question: ‘don’t these island creatures know an enemy when they see one?’ And the answer is, somewhat surprisingly, ‘no’. Or more accurately, ‘not anymore’. Fear is an adaptive trait, useful for avoiding predators and undue risks. However fear is an extremely costly trait, and hence animals on islands with no natural predators tend to lose their fear rather quickly. Stories abound of Dodos practically walking into the cooking pots of Dutch sailors and Galapagos finches feeding from the hand of Darwin; not so much fish in a barrel as birds on an island. Lack of fear therefore, is the characteristic that makes islanders so endearing and so endangered in the same breath.
Mass extinctions occur when the change of pace is accelerated to such an extent that most species cannot keep up; their time has literally run out. The current rate at which species are being lost is faster than practically any other time in life’s history. We are amidst the sixth mass extinction event. Human beings, and particularly industrial societies, have brought about a sense of rapidity that leaves all others in the dust. The inherently slow pace of island life results in such tropical paradises acting as the canaries in the coal mine. The likes of moas, pygmy elephants, and Irish elk, are sadly now spoken of in the past tense. And the situation is going to get worse before it gets better. Komodo dragons giant tortoises and tuataras are on the way out. People are only becoming more numerous and more mobile. It is now possible to fly halfway round the world in less than 16 hours. It is now possible to book a package holiday to Tristan da Cunha. Nowhere is safe, nowhere too remote to avoid the ongoing pandemic. We are orchestrating a transition from desert island to deserted island. Before long entire archipelagos will be reduced to nothing but rubble. Picture it. A tropical paradise, blonde sands calmly caressed by the cool blue, a gentle ocean breeze brings rotting carcasses and cat shit to the nostrils, an eerie unnatural silence fills the ear. The fate of the islands today will be the fate of the continents tomorrow. If we want to stem the loss of biodiversity on this planet, now’s the time.
The sun is rising. Huddled beneath the crown of an ancient oak, I take in my surroundings. The early-morning mist hangs on the forest floor. It will be several hours before it dissipates. It is still cool enough that I can see my breath, and the woodland birds sound lethargic, chilled from the night before. The sun’s rays are sepia-toned and fractured as they pass through a tangle of tree branches. A stag emerges from the gloom, equal parts mythical and majestic as it meanders through the copse. It wanders close enough for me to see its glistening fur, to see its nostrils flare. Closing my eyes, I hear my heartbeat. I hear rustling leaves. A branch snaps underfoot, a grouse flushes from the thicket. Not a moment to lose, I raise the bow to my eye and take aim. The time is now.
Analog vs Digital
The time you enjoy wasting is not wasted time.
~ Bertrand Russell
The Big Sleep
A chipmunk scurries through the undergrowth. The faint rustle of leaves is the only indication of its presence in the tangle of thickets. The acorn crop this year was not particularly bountiful, and as such the search for food is a full time occupation. As the days get shorter and temperatures wane, foraging behaviour becomes increasingly frantic. Soon the rodent will be forced underground. At the mountain’s peak, the winters are harsh enough to drive the entire forest into a state of torpor. The hickory will hibernate, the spruce will slumber; silence will fill the air. The resident birds will descend the mountain slopes to escape the icy conditions, spending the colder months in more congenial locales. The gift of flight becomes stark in such a landscape of extremes. Many of the creatures not afforded this luxury will succumb to the elements before season’s end, frigid and frost-bitten. For the chipmunk to survive it must find a subterranean retreat, lower its vital rates, and wait.
Noah notwithstanding, nothing comes in twos. The fallacy of ‘either-or’ thinking pervades our society. True or false, this or that, them or us. The simplicity appeals to our primitive minds. Although much can be done with zeros and ones, indeed the digital age has shown us quite how much, there is inevitably information lost when continuous information is chopped up and put into arbitrary categories. Cat-owners and dog-owners are two labels that we have invented, both of which come with stereotypes, staunch advocates, and self identification. Yet these labels are the crudest representation of millions of people, each with unique ideas and philosophies. Moreover the dichotomy acts to obscure people who do not fall into either category - people without pets, people with goldfish or hamsters - these people are erased from one’s mind. From pet ownership to politics, the notion that we live in a binary world is firmly entrenched in the human psyche.
Although science seeks to better understand the world, most disciplines are similarly burdened with false dichotomies. In the first half of the 20th century, physicists fiercely debated as to whether light was a wave or a particle, until discovering it was both. Or more accurately neither. It is interesting to ponder on the question of whether in this instance scientific progress was hampered, owing to the trenchant view that light must be one of the two favoured options, or whether greater advances were made, when the in-fighting spurred on research labs to design the ingenious experiments that finally put the debate to rest. Good or bad? I am confident it is not as simple as that. All that we know for certain is that scientific breakthroughs were made, paradigms shifted, and the now infamous revolution began to take shape. Of course, opinions did not change overnight; we are blessed with a century of hindsight with which to interpret the birth of quantum physics, and still the properties of light, the way it behaves like nothing we know, is not fully grasped by the average person. The ‘either-or’ fallacy is salient. As a result, the true diversity and infinite variety of nature remains hidden to most.
The biological sciences have their fair share of false dichotomies. Whilst several associated with people are being challenged (e.g., sexuality, gender identity), we still have a long way to go. Traditional beliefs are deeply rooted and tricky to shake; new ideas in science do not come about because opponents are won over by convincing arguments, but because eventually all the people that believed the old theory die off. The key then is to indoctrinate future generations with a more comprehensive view of the world, a more accurate picture of the universe’s grandeur. To do this we must overcome the deficiencies of ‘either-or’ thinking, which ultimately stem from deficiencies in language. Our words provide a window into the true nature of reality, but we must always be careful not to confuse the two. Clunky metaphors can obfuscate where they are meant to clarify. A lack of creativity will certainly limit the power of young minds to absorb and fully appreciate their surroundings, and thus they must learn that art is as much a part of science as science is a part of art.
Meet the Parents
The nature versus nurture debate has raged amongst psychologists for decades. Are traits inherited or learned? Are personalities shaped by genetics or the environment? Parents are bombarded with books and blog posts, so-called experts fervently advocate for one parenting style over another. If nature overwhelms nurture, then mothers and fathers are largely helpless as to the outcome of their offspring. If nurture is the key, then are parents ultimately to blame for a wayward child? Such rhetorical questions emerge from ‘either-or’ thinking, and are not worth our time here. Instead we should turn to the animal kingdom to shed light on the true nature of nurture, the intricate, interwoven tapestry of genes and ecology that shape an organism, and the infinite variety of strategies available to would-be parents.
Care comes in many forms, and can be extensive or rather limited. The effort parents are willing to expend on their children is driven by many factors. Any parent must weigh the costs of care with the potential benefits. The benefits are obvious - increased offspring survival rates. Costs emerge from the massive energy expenditure associated with care, potentially jeopardising survival of the parent or reducing future reproductive opportunities. If these costs are too great, then no care is afforded. Sex-specific costs also exist, and these help to explain why in some species the mother provides the bulk of the care, whilst in others it is the father that assumes the parental responsibilities. For mothers, perhaps the most important consideration in the degree of care she will afford her offspring is egg size. Large eggs are inherently more valuable because they are more likely to survive to breeding age themselves, and as such, ‘motherly love’ is typically only seen in animals with big babies. Fathers in contrast, when deciding on how much care to provide, must take into consideration such things as the likelihood of paternity and the number of additional mates they could potentially secure if they eschewed their duties. Our mammalian ancestry biases our thinking towards maternal care being dominant, so it may come as a surprise that paternal care is more common in many groups – fish, frogs, and several crocodilians harbour some exceptionally devoted fathers. Birds are the only group of animals in which care by both parents is the norm. Apparently, it is a rather unusual set of circumstances where the benefits of care outweigh the costs for both parents.
Every step of the parenting journey is costly and exhausting, such that extended care of young, beyond nest-building or egg-guarding, is rare. Constructing a nest alone can be a laborious, time-consuming activity. In many fish species, eggs are simply expelled, left to drift in the currents or nestle on the seafloor. This is clearly the simplest strategy, with the least cost to the mother, but it is not the most efficient. Some fish must produce as many as 50 million eggs every year to have any chance of siring future generations. Like dandelion seeds on the wind, most are swept to inhospitable locations and perish. A nest therefore, might allow you to save some energy, despite the cost of producing it, by ensuring that your progeny start off life in the right place. The foam nests of certain frogs and insects for example, not only keep eggs hydrated, but also hide the eggs from potential predators. Having journeyed for thousands of miles upstream, Pacific salmon create small depressions in the riverbed gravel to deposit their eggs into. Although seemingly innocuous cavities, and the effort of creating them largely eclipsed by the monumental migration they have just undertaken, parents will fight tooth and nail to defend their spawning sites, suggesting the nest can make all the difference to hatching success. Alas, the salmon are not privy to the fate of their offspring; the cost of ensuring the survival of their progeny is ultimate. By laying their eggs in the nests of other birds, cuckoos enjoy all the benefits of care without incurring the costs. Indeed the energy saved by not having to build their own nests allow cuckoos to produce more offspring, perhaps ten times more, than the birds whose nests they are parasitizing.
For many animals, building a nest or finding a safe refuge for their eggs is as far as they’re willing to go, as much energy as they are willing to spend in securing their contributions to future generations. Others however, continue to invest in their offspring. Eggs can be guarded, offspring can be provisioned. Viviparity is a combination of guarding and provisioning. Once thought to be a feature unique to mammals, viviparity, the process of giving birth to live young, is widespread in the animal kingdom. Live birth has allowed lizards to colonize some of the coldest environments on earth. If you ascend the French Alps and examine the lizards as you climb, you will notice that the duration between mothers laying eggs and the eggs hatching gets shorter and shorter. As you approach the summit, you will not find any eggs at all. As temperatures drop and the risk of freezing increases, females retain eggs for longer periods to protect them from the elements. At a certain point, eggs are retained for their entire duration and mothers give birth to live offspring. The new avenue for mothers to provide nutrients to their developing embryos is also rather handy; placental structures resembling those of mammals have been identified in sharks, snakes, and lizards.
Life on water versus life on land is perhaps one of the starchest dichotomies in the biological sciences. Yet even this distinction is not as clearcut, not as binary, as it first appears. For a start, both habitats can be broken down into a plethora of sub-divisions with convincing legitimacy. Terrestrial species come in at least three types: those in the air, those underground, and those truly on the land. Similarly, aquatic species can be split into freshwater and saltwater. But then we might feel inclined to further split the oceans into myriad distinct realms based on depth, availability of sunlight, and temperature. Perhaps we create an additional group for the animals that inhabit the brackish water of estuaries? Indeed scientists do this routinely, and the jargon betrays this constant dissatisfaction with grouping systems - lentic vs lotic, lacustrine vs palustrine, pelagic vs benthic. False dichotomies within false dichotomies. We live in a world of infinite variety, but our method of comprehension, namely language, forces us to compartmentalise. Most biology is now conducted in the language of mathematics; tired of enduring the limitations imposed by words, exasperated scientists have turned to numbers to better capture the continuity of nature.
Thousands of animals saunter between water and land as if it was nothing. Amphibians and insects alike show a complete disregard for our binary worldview. Starting off life in the water has significant advantages - food is plentiful, and a prospective mother can be reasonably confident that her eggs will not freeze or dry out. Glass frogs in Central America however, opt for a different strategy. Given the humidity of the tropical climate, frogs that live towards the equator can deposit their eggs on land without too much risk of desiccation. Were they to place their eggs directly in the water as most temperate frogs do, they would be devoured by fish. Many of these eggs will hatch out into miniature frogs, such that the aquatic stage is skipped entirely, but the eggs of glass frogs hatch into typical larvae, and must therefore be deposited on vegetation that overhangs rainforest streams. Suspended on a leaf though, does not come without potential hazards. For this strategy to work, the father will remain with the clutch until they hatch and drop into the water below. By sitting on top of the eggs he can keep them moist throughout their development and defend them from would-be predators. The father’s duties extend until hatching and no further; for the most part, adult frogs cannot follow their tadpoles into the water. Predators are abundant in aquatic environments however, and so without parental care, frog tadpoles typically grow at breakneck speeds in order to reach sizes that will permit metamorphosis, upon which point they exit the water as fast as possible. An alternative strategy is to attain such a large size that you effectively outgrow your predators, and are thus able to enjoy a more leisurely, sometimes permanent, existence in the water. All of the largest salamanders - hellbenders, mudpuppies, eel-like amphiumas and sirens - are fully aquatic. A whole host of amphibians are not amphibious; again our language limits our understanding.
Amphibians are some of the most threatened animals on the planet. A flood of extinctions is underway. Habitat destruction and a killer fungus are rendering the natural world inhospitable, and as a result, frogs and toads are being rounded up and stashed in zoos around the world. In captivity, conservationists are attempting to develop assurance colonies, a last-resort intervention, in the hopes that one day the habitat will be restored, or the fungus eradicated, and animals can be reintroduced to the wild. The two-stage life cycle of amphibians puts them in a situation of double jeopardy. Their aquatic homes may be in pristine condition, but if deforestation renders their terrestrial environment uninhabitable, numbers will crash. Or the forests may be fine, but if all the breeding wetlands have been drained, the population will no longer be sustainable. Multiple synergistic threats, impacting multiple stages of an organism’s intricate life history - the situation is complicated. Nobody knows the solution, hence the proliferation of amphibian ‘arks’, temporary stopgaps as we race to understand the problems and turn the tides. Knowledge is power, but will it be science or faith that saves the day?
A rattlesnake sits motionless at the base of a white pine. It has not moved for two months. Intricately patterned, subtly coloured, umber hourglasses, copper diamonds; the animal is indistinguishable from the forest floor. The serpent is an ambush expert, with the patience of a saint, and the cold-bloodedness of a killer. Suddenly, it tastes the air. Something is coming. The evening sun filters through the canopy, and scales glimmer as coils loosen. Imperceptibly, it adjusts its position to align with the prevailing wind, nose to the breeze, eyes on the scent. It retracts its neck with the newly created kink acting as a slingshot. The strike will last less than a fraction of a second. As the chipmunk approaches, muscles contract as tension fills the heavy midsummer air. Death is an instant. Death is eternal.
In the Midnight Hour
I’m gonna wait till the stars come out
And see that twinkle in your eyes
I’m gonna wait ‘till the midnight hour
That’s when my love begins to shine
~ Wilson Pickett
A tropical paradise, blonde sands calmly caressed by the cool blue, a gentle ocean breeze brings salt and seaweed to the nostrils, and unseen birds bring a sweet melodious symphony to the ear. Sarah methodically excavates the nest, using her hands to remove the recently disturbed sand. The eggs, two hundred or so, are placed in a tupperware container, with the utmost care taken to keep them upright. Unlike bird’s, sea turtle embryos will die if the egg is turned upside down. They are transported back to the captive facility, and delicately placed in an incubation chamber, shielded from the elements and safe from predators. In a few months time the newly-emerged hatchlings will be released into the Pacific ocean. Unbeknownst to everyone involved, they will all be males. Next year even fewer turtles will visit the beach to lay their eggs.
Night Time is the Right Time
The timing of reproduction has fascinated biologists and crooners alike. Time of day, time of year, time of life - it all matters. Every species operates on a different schedule, intricately shaped by myriad features of the environment that render particular strategies optimal. Salmon in the Pacific ocean breed once in their lifetime and die. Salmon in the Atlantic breed multiple times. Why? On the Pacific side, the journey upriver to spawning grounds is more perilous - more rapids to fight, more waterfalls to ascend. As such, the Coho are far less likely to survive the return journey back out to sea, let alone repeat the migratory feat every year. Therefore for the Alaskan fish, it is a safer strategy to put all their eggs in one basket, literally, and invest everything in a single breeding event. The same type of decision making process can be evoked when contemplating annual versus perennial plants - namely, how likely are you to survive the winter? If you are sure to die before your second reproductive opportunity, you should divert your energy to producing offspring immediately. If you are sure to die before your first reproductive opportunity, your species is not long for this world.
Like humans, frogs are certainly nocturnal lovers. In general, amphibians are more active at night. If you have skin that must stay moist in order that you can breathe, the sun is the enemy. Wind is a problem too, and most amphibian behaviour can be understood in terms of ensuring that one doesn’t dry out. When breeding commences, the benefits of nocturnal activity are amplified. Particularly for males that do the majority of calling, every croak risks revealing your location to wouldbe predators – birds would have a field day if frog choruses occurred during the daylight hours.
Males frogs typically begin calling at breeding sites before females have even arrived. This is not altogether intuitive. A very specific set of environmental conditions is typically required for amphibian reproduction, and besides, why would males rock up before there is anybody to impress? In territorial species, perhaps early arrival allows you to stake out a good patch. Yet we see such staggered arrival in the majority of species, so there must be a deeper, more fundamental explanation. It appears to derive from the different relationships between how many times you breed and your overall fitness. For males, the more females you mate with, the more progeny you sire. For females however, it doesn’t really matter whether you mate with one or ten males, you produce the same number of offspring regardless.
The idea that males care about quantity whereas females are more concerned with quality underpins all sexual selection theory. In the context of staggered entry at breeding sites, males typically arrive as early as possible to maximise their mating opportunities across the breeding season, whereas females delay arrival to maximise the available choice of potential suitors. From the perspective of an expectant mother, if there are many males, she can afford to be choosy, if there are few, she may have to make do with the best of a bad lot. In situations where females are relatively scarce, competition between males can be a matter of life and death. Indeed, the degree of fighting is strongly correlated with the ratio of males to females in animal populations. Humans as well, show similar proclivities. In bars and clubs around the world, where competition is fierce, fighting for females is a nightly occurrence. In the modern age however, new avenues have opened up for weaker men to impress females; art certainly, humour most definitely. There are always multiple viable strategies in nature. Perhaps this essay is my own personal way of impressing the ladies… boy I hope it works - sooner rather than later.
Winter, Spring, Summer, or Fall
Although they may wait till late in the day, many amphibians commence breeding early in the year. Around the temperate world, frog choruses are one of the earliest and most reliable signs of the changing seasons. A ubiquitous species in North America, the Spring Peeper is so named because despite the resemblance of its call to sleigh bells, its emergence in March is as predictable as daffodils and tulips. As a rule, cold-blooded species are far more in tune with the vagaries of the calendar, their behaviour and biology is intrinsically linked to the outside temperatures. Spring breeding is the norm, not simply because it is when most amphibians emerge from their winter slumber, but because it will give tadpoles the best start in life - an entire summer to find food, grow, and develop into miniature versions of their parents. With everybody trying to lay eggs at the same time however, a scramble for resources emerges and competition generates few winners and far more losers. Devising strategies to avoid the crowds would yield substantial benefits.
Against the grain, the marbled salamander lays its eggs in September. At this time of year, the woodlands they inhabit are dry. One would be forgiven for thinking these animals have chosen the wrong time to breed. As temperatures begin to drop, and leaves begin to turn, a female will march across the forest floor, back to the place she was born. On reaching her destination, she will place a clump of eggs on the forest floor, and wrap her body around them to keep them moist. Strange behaviour for an amphibian. But there is something stirring in the air, change is on the horizon. After several weeks the rains come. As the ground saturates, lower lying areas begin to pool with water, and the expectant mothers, along with their clutches, are inundated. Now the eggs can hatch, and with very few competitors and a head-start on development, marbled salamander larvae quickly rise to the top of the food chain. To the likes of wood frogs that do not arrive until February, marbled salamanders represent formidable predators. They have already grown to several inches in length, dwarfing their cohabitants. In the six weeks required for wood frog tadpoles to complete development, they will suffer heavy losses. By May, the ponds have dried up, anything big enough to metamorphose has done so, everything else has perished. After the dry spell of summer, the rains will return, and the struggle for existence will begin again. In these short-lived aquatic realms, timing is everything.
Much recent attention has been given to whether the timing of reproduction will shift in response to climate change. At northern latitudes in the spring, frog choruses can be heard two weeks earlier as a result of global warming. This is not a trivial amount of time. For species that exploit small temporary wetlands that appear briefly following seasonal rains, the entire breeding season might last less than two weeks. Clearly if the shift in timing matches changes in rainfall or ice melting, then the frogs will persist, but serious problems will arise if species alter their behaviour and as a result miss the opportunity to breed. Phenological mismatches, as these phenomena are called, are rife and only expected to become more common. If female frogs arrive before their male counterparts, the entire fabric of sexual selection will crumble; survival of the fittest will turn to survival of the desperate. If marbled salamanders migrate too early, their eggs will dry out, too late, and all the prime egg-laying habitat will be underwater. If fruit-bearing trees ripen earlier than usual with rising temperatures, migratory birds must adjust their overwintering schedules accordingly or risk starving. In turn, if the birds cannot adapt quickly enough, the trees will lose their main source of seed dispersal. The impact of phenological mismatches is boundless; ecosystems may collapse.
Now’s the Time
In the neotropical rainforests of central and south America, from Panama to Peru, there is an epidermis epidemic. The chytrid fungus originated in Asia, and was transported across the globe via the pet and commercial trades of amphibians. Chytrid is one of the most generalist diseases known to man. There are over 6000 species of frog on earth, and Chytrid will infect virtually all of them. The very trait that defines amphibians is their downfall; porous skin provides no barrier to the fungal spores, and individuals are slowly suffocated as the disease enshrouds their bodies. Even if the pathogen does not get every last frog, populations will be left in tatters, teetering on the brink of collapse. Populations’ crash, and the once-heard lively midnight choruses have dwindled and become lonely plaintiff cries.
Is there anything more soul-crushing? Imagine The Rat-Pack, or any other crooner from the golden age of singers performing to an empty concert hall. Sinatra, baring his soul, with nothing but his echo reverberating off the bare walls in reply. The power of the artistry on display becomes heightened, as the emotional content of the lyrics is starkly juxtaposed with the futility of the performance. And perhaps there is an additional sullen reminder of the heights of the past. In music this happens at venues the world over, as popular tastes change and musical styles go in and out of vogue; in frogs this happens at wetlands across the globe as audiences are decimated by the deadly fungus, and lonely males are left to lament into the void. When populations are driven to such low numbers, the risk of extinction is perilously inflated. The perpetual struggle to find mates, low genetic diversity, and natural catastrophes, all help to stack the odds against small populations. Eventually every singer gives up the ghost, entire species blink out, and both the songs and admiring masses are consigned to the annals of history.
The mechanised clockwork of industrialization, the insistent march of a very unnatural drum, will spell the demise of many a species. Modern travel is a way to save time. But it does not come for free. We are already paying the price of near instantaneous circumnavigation of the planet. The global flow of humans facilitates the global flow of pathogens and pests. Even if Chytrid is completely eradicated from the environment, the recovery of frogs remains in doubt. Final curtains have fallen at least 200 times in our lifetime, likely considerably more. Potential solutions do not come easy; captive colonies are on the rise, but these animal arks represent only a temporary stop gap until a permanent remedy is divined. A world without frogs will be a sad world indeed. Without immediate global action, a silent night will leave us all mourning. In the modern age, animals are in jeopardy. Do not ask for whom the bell tolls. Right now, the bell is incessant, and it is ringing for everybody.
The clock strikes twelve. Lights flicker in the midnight sky, as strong winds ride in from offshore. On the beach, new life is emerging. Hatchling sea turtles, no bigger than the palm of your hand, push their way up through a ceiling of sand to taste the salt-filled air. First a couple, then dozens, then scores. Hatching is synchronised so as to saturate predators - they will inevitably devour some of us, but with luck they will not devour us all. An army of ancient armoured reptiles head towards the surf, aligning themselves with the moon and stars overhead. The odds are stacked against them. Only one in a hundred will likely survive to adulthood. House music drifts through the breeze, the roar of traffic grows ever louder, the incessant chatter of tourists resembles a dawn chorus in a pristine rainforest. Confused by the street lamps, disoriented by the human soundscape, the infants are off course. One by one, turtles tumble down a grate and are swept into the sewer. Across the road outside the bar, a cheer goes up as a glass is smashed on the concrete pavement.
A Change of Pace
Let us not be particular and sectional. The poet’s mind and the scorpion’s tail rise in glory from the same earth.
~ Kahlil Gibran
The Apes of Wrath
By 7am, the lorry queue stretches back onto the main road. One by one they drive up to the barrier and converse with the station attendant. Paperwork is handed over, pleasantries are exchanged. On occasion a small fee surreptitiously changes hands. The barrier swings up and down with monotonous regularity, as trucks enter the site, turn right at the main office and descend single-file along the winding dirt thoroughfare. It is November. At this time of year the relentless drizzle has transformed the temporary road surface into a quagmire. Sludge that will steal a boot if you give it the chance. Mud up to the knee. Many of the arriving vehicles will require assistance on their journey. Towing is essential to keep things running smoothly and on time. At a certain point the path forks, and directions are translated to the drivers. General? straight ahead. Chemical? round to the left. Asbestos? follow the yellow dumper. Each type of cargo has its own pile, its own burial site. If all goes to plan, the line of trucks by the entrance will abate around lunchtime.
The Spice of Life
Diversity is the most interesting thing about the natural world. The myriad ways living things partition their resources into growth, survival, and reproduction, is as extraordinary as it is unfathomable. Such diversity could only have emerged over colossal timescales. Luckily for us, the universe is indeed stupendously ancient. On planet Earth, life has had 4,000,000,000,000 years to prosper and flourish. Eons of experimentation and refinement has resulted in starfish and sequoias, toads and toadstools, elephants and E. coli. Clearly there are many ways to skin a cat.
Most living things have complex life cycles. By far, the most abundant land animals are the insects, and virtually all have multiple life stages and elaborate life histories. Mayflies famously only live for a day. In late spring, each female must find a mate within a vast breeding swarm, fertilise her precious brood, and carefully deposit her eggs on the water’s surface. All to ensure the continuation of her lineage. All within 24 hours. A fleeting existence one might suppose, but many of these hopeful mothers have waited years for this moment. The larval stage of the mayfly enjoys a positively sedate way of life in comparison. Nestled amongst the rocks on the stream bed, the nymph will do little more than clamber about, occasionally chewing on decaying leaf litter that has sunk to the bottom. For more than 700 days, the mayfly will engage in this pottering behaviour. But nothing lasts forever, eventually the aquatic invertebrate will receive environmental cues that signal it’s time to breed. The biological clock waits for no man, all good things must come to an end, come what May.
Most frogs and salamanders show the opposite trend in the pacing of their lives. As a rule, amphibians are fast in water and slow on land. The growth of tadpoles is typically rapid to minimise the time spent living alongside predatory fish. Moreover, many species will put their eggs in puddles that will eventually dry up; in the race to metamorphose before water levels recede, the stakes are high. To dawdle would spell disaster. Once emerging however, amphibians on the land can afford to take their foot off the gas. Many salamanders live for decades on land, hunkering underground for the most part, occasionally breeding when conditions are right. Contrast such as these are a commonality of life on earth, a change of pace represents the norm. Without this, life would be far less diverse, evolution would tend to one homogenous mass. In turn, too much contrast can also prove detrimental to nature’s flourishing.
If life has adapted to anything, it has adapted to change. By and large, our world is one of moderate, somewhat predictable change. The seasons change gradually, the tides take several hours to advance and retreat, sunsets are picturesquely slow. This is what living organisms have evolved to cope with. Change is the only constant. Whilst most things can tolerate, or indeed anticipate, some change, change too abrupt can often have disastrous consequences. It is cemented in biological theory that all living things are in a sprint. Evolutionary arms races - between parasite and host, between predator and prey, even between parent and offspring - mean that there is not a moment to stand still. To do so would spell disaster. Whilst all those around you are running to get ahead, you must follow suit or risk falling by the wayside. Life then, diversity, has originated in a dynamic, high-speed environment. But now it is feared, the world is changing so fast that even the swiftest species cannot keep up. Said the Red Queen to Alice, “Run as fast as you can. Or thrice as fast as that. It makes no difference, you will still be left in the dust.”
Done Changed My Way of Living
Change is not brought about by choice. Change occurs as a necessity, a response to outside forces that deem it to be so. Space and time are one and the same, such that changes through time are synonymous with changes across space. It can be difficult however, to disentangle the two, especially when one is constantly on the move. If you begin to contemplate some of the great nature writers in history, those that gleaned real insight into the inner workings of the natural world, you realise they all resided in one place. Gilbert White’s parishioners would have undoubtedly been irked if he had constantly been upping sticks to gallivant around on various cross-country jaunts. Aldo Leopold never strayed too far from his Wisconsin shack. Thoreau’s cabin is central to Walden’s narrative. Changes through time can only truly be appreciated if you stand still. Only then, once you have got to grips with how things work at a single location, can you begin to compare changes through time here to changes through time there. To view the world in all its four-dimensional splendour, to achieve the feat first managed by Darwin and Wallace, is to know thy maker. But you must walk before you can run.
Stuck at home during the 2020 pandemic, the constant flux of my backyard became crystal clear. The changing seasons were inescapable. The stark juxtaposition of monotony and uniqueness was ever at the fore. In twelve months of lockdown, I lost count of the things I observed on only a single occasion. Only once was I visited by a pair of pileated woodpeckers. For an hour or so they investigated the base of the white oak that stands proudly in the centre of my lawn. And then, as soon as they had arrived they departed, never to return. Only once did a turkey grace my presence. Only once did I glimpse a grey fox, scurrying through the tangle of thickets by the fenceline. Although the resident groundhog was a common sight during the summer months, only once did I observe it off the ground. On a warm September evening I spied the animal climbing the trunk of a small hickory, where it proceeded to recline on one of the horizontal branches. Dappled in the evening , it seemed to have all the time in the world. Yet no sooner than it had got comfortable, was it spooked by the shadows of hawks flying overhead, whereupon it hurriedly descended down the tree and retreated to the safety of its burrow. If it performed this feat again, I was not witness to it. In our attempt to explain the natural world in all its refined glory, we sometimes lose sight of its capriciousness. Our minds cling to order, such that we are hard pressed to acknowledge the role of chance.
Every living organism rolls the dice. The 15,000 seeds produced by the humble dandelion, or the 340 million eggs of the grey grouper, speak to the lottery of life. Whether sacrificed to the breeze or expelled into the ocean, hope is all that sustains them. The future is unknowable - plants and animals know this. The most successful strategists are the bet-hedgers, those that put their stakes in multiple metaphorical baskets. Dispersing your offspring as far and as wide as possible accounts for the heterogeneity of landscapes, but only time will tell if such efforts prove fruitful. Newts are limited in their capacity to spread risk by the small nature of the ponds they inhabit. But within this narrow confinement, females will deposit their 200 eggs throughout the basin. Skirting the pond margins, a mother will affix each one of her spawn to its own piece of submerged vegetation, figuring it will reduce the likelihood that predators will uncover them all. For any surviving progeny that make it out of the water, they will traverse the wider world in the hopes of stumbling upon brighter pastures - a pond of their own with perchance, fewer predators or cleaner water. In time, the newts will spread to occupy all inhabitable wetlands, each with its own unique climate and opportunities to thrive. With the risk spread across space, the plucky amphibians are less prone to fall victim to droughts or drainage.
As any engineer will tell you, resiliency is the capacity of an object to recover from disturbance. In recent years the biologists have appropriated this terminology, and refer to it when making assessments of ecosystem health and evaluating nature’s ability to withstand global change. Again we learn from the engineering world that redundancy heightens resiliency. Environments are most resilient when they contain a multitude of species that overlap in form and function. All things being equal then, a loss of biodiversity equates to a loss of resiliency. To lose species from an ecosystem can act to undermine the myriad processes and interactions that comprise it. Ultimately, ecological communities that are not resilient to external pressures will be replaced.
The modern world is a turbulent period in earth’s history. We are currently witnessing a changing of the guards; human actions have destabilised entire biomes. Many natural areas lie on the brink of collapse; no longer resilient, the slightest perturbation could spell their demise. The great boreal forests, once resolute, capable of tolerating fire and ice, are now threatened by a small, burrowing beetle. The great barrier reef, once immutable in the face of immense storm surges, is now crumbling due to a slight change in water chemistry. Nature is revolting; angered by their plight, battered and bruised from decades of mistreatment, life on earth is spearheading an upheaval, a new world order. Regrettably yet unsurprisingly, we as a species do not feature in the image of the future being formed.
Mass extinctions are always size dependent; big things are disproportionately affected. They require space that is no longer available, they require time that is no longer afforded to them. When catastrophe strikes, species in the slow lane that have grown accustomed to a leisurely existence in earth’s most stable environments are first for the chop. Nothing bigger than a domestic cat made it through the K/T boundary. The contrasting fates of birds and pterosaurs is case in point. Flying lizards as big as light aircraft are no longer with us. Why not? As discussed, flight permits animals to avoid harsh conditions, so why were these winged giants not spared from the K/T mass extinction? Most likely because they were giants. In our time, very few creatures that fly are as big as cats, and none are as big as pterosaurs.
The sixth mass extinction will likely also be size-dependent. So called megafauna were the first to go at the onset of the Anthropocene. Mammoths, Moas, and Ground Sloths were all too slow for the pace of primitive man. The largest birds show worrying trajectories. The likes of Albatross and Condors are too big, and have life-histories that are too slow, for the modern pace of change. Before long, I fear we will consider them alongside pterosaurs as mythical giants. Yet the world is reconfiguring itself with such speed and force, that even small, inconspicuous creatures are being swept up in the melee. Precarious positions are occupied by the lowly golden toad, the timid Kirtland’s warbler, and the unassuming checkerspot butterfly. The extinction debt we have accrued through our mindless activities, our egotistical adventuring, must be paid in full. There will be few survivors. Instability begets instability. Uncertainty is the hallmark of change, but disorder is certainly the endgame. Our time is up.
The test strip turns red. Once again, the pollution levels have been exceeded. Every month the off-site discharge rates are far beyond those permitted. The fines are beginning to accrue. On Tuesdays the creek runs black with leachate, a toxic, tar-like cocktail that collects and festers in the bowels of every modern landfill. On Wednesdays the retention ponds are drained, and the resulting slurry transferred into the neighbouring wetland. Scum clings to the rocks and reeds. Fish have long since abandoned this stretch of waterway. The site has been in operation since the 1960’s and has almost reached capacity. Soon it will be converted into a historic landfill. Engineers will work tirelessly to remove sumps, install gas wells, and cap the top of the cell with propylene liner. A thin layer of dirt will then be spread across the plastic surface, and seeds sprinkled liberally throughout. In just a few years the site will resemble a grassy hill, and could be mistaken for a natural feature of the landscape. But for several centuries, the waste beneath the surface will continue to generate methane, hydrogen sulphide, and ammonia, in concentrations that could kill a horse. Nevertheless, when all is said and done, the workers can go home, satisfied with a job well done.