Month: January 2022

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. 

Coda
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.

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

Canary Row
“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 moustache 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 lifeform 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 80lb 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.

Time Flies
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.

Coda
“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 pickaxe 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 mineshaft. 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.”

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.

Theory without facts is fantasy, but facts without theory is chaos. 
~ Charles Otis Whitman

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.