Imagine, for a second, that you’re on a quiz show. Really, do. Look up from your screen and see the white-hot lights, the studio audience, feel your heart drumming quick cadences. Your hand flutters over the buzzer, because this is it: the million-dollar-moment, for all the marbles, to win a new car, perhaps a trip to Jamaica. The host’s voice booms out the question: “According to conventional estimates, what is the current number of extant—that’s the opposite of extinct, folks—species on Earth?”
Go ahead. Take your time—no need to lock in on that buzzer, yet. Think hard… because it’s not an easy answer, is it?
In simplest terms, the million-dollar-question revolves around a central topic: biodiversity. How often do you consider this subject? Do you ever mull it over when your head hits the pillow, chew on it over a bowl of cereal, toss a casual mention to the grocery store clerk? First coined in the mid-1980’s as a natural contraction of “biological diversity,” at first glance biodiversity appears relatively straight-forward. Standard definition deems it the variety and variability of life on Earth, a sort of all-encompassing census that is further triaged into narrowing levels of specificity: within global and regional ecosystems; amongst habitats; and even taking into account genetic and phenotypic variation within a species.
By textbook terms, the frameworks of biodiversity are thus established. However, as walking, breathing, fortunate members of the community of life, our human dependency—and intimate relation—to all beings roots infinitely deeper than this subject’s surface layer. To begin, therefore, we must look beyond ourselves, to other lifeforms and other long-ago times.
Consider: if presented with a sort of metaphysical wager during the wee dawn of the universe, life’s emergence would not be a good bet to make. As first touched upon in our “Welcome to Earth / Deep Time” article, the story of Earth, and all of its biological richness, is a highly improbable one—perhaps the most unlikely known to exist. It’s a story that unfolds on an unimaginably broad timeline, with rich, diverse life occupying but the tiniest sliver: some 10 billion years coming and going between the Big Bang and the planet’s first microorganisms. It wasn’t until approximately 3.7 billion years ago that the spark was struck—a chance melding of cosmic elements on a young, hostile Earth that happened to scrape the flintstone for life. It is impossible to prove just how improbable the coming of these single-celled beings was, but it is certain that all life, present and past, is descended from it.
Though lineage is often perceived in a linear fashion—and though it is accurate that all extant species and individuals have their own wondrous, unbroken chain of a survival story through time—it may be more useful to view Earth’s biodiversity as something more enmeshed.
If life is to be deemed a web, rather than a series of disparate chains, then this long-ago, chance event is much like the initial molecule—or pinprick—of the very first strand. Analyzing humanity in such a manner, then, we see more clearly the nuances of our place amongst this interrelatedness. Within the web of life, we’re more directly connected to some, our neighboring strands; less so to others, species along somewhat divergent evolutionary paths. Nevertheless, each is in some way tethered to every other, and no strand is woven nor survives in isolation, drifting listlessly on a lonely breeze.
DNA commonality provides one useful mechanism to see these linkages: humans, Homo sapiens, for example, share approximately 99% of their genetic sequencing with chimpanzees, 90% with cats, 85% with mice, 61% with fruit flies, and 60%…with bananas. Ridiculous though that may sound, inter-species kinship is quite literally coded into our very fabric. We also possess a litany of vestigial structures—from elements of fish eyes to taillessness—which shed further light on common origins.
All of which should, perhaps, serve to humble us. Diversity is birthed from solidarity, beget by symbiosis and coevolution. Whether the grandest redwood, most revered king, dainty fern, or gentle mouse, we all ride the tides of time and chance together. More fundamentally, every living being is a formation of the same cosmic dust, now bobbing along together on a delicate blue speck in a rippling, stellar ocean.
But, again, the richness of Earth’s biodiversity—its teeming soils, its vast, mysterious waters, its chorusing wooded ecosystems—is not only precious, but unlikely. Through unimaginable eons of cosmic, then biogeophysical roiling, billions upon billions of events and encounters just so happened to occur in the manner they have—allowing conditions for Earth’s remarkable biosphere to develop. It may be quite easy, or even natural, for us as humans to romanticize this longest of evolutionary games. We’re prey to a certain survivorship fallacy, which imbues a sense of retroactive intentionality to the course of both Earth’s, and especially our, comings. In other words, since we’re currently here, and an estimated 99.9% of all species to ever live are not (either extinct or speciated), it often feels as though things must have been predestined this way. This is a phenomenon partially defined under teleology—and comforting, yet misleading elements of false intention are sewn into many dominant religious and cultural narratives. Those surrounding creation and evolution often triage biodiversity to their own ends, placing humans at the pinnacle of species hierarchies.
Ironically, however, not all life is given rise by equal chance, and Homo sapiens is in fact amongst those species least likely, in ecological terms, to have evolved. As far as our human reasoning has deduced, large, complex life—often categorized together in biology as K-selected—may be exceedingly, extraordinarily rare. Through a myriad of extinction periods and generally inhospitable conditions, Earth history has not been kind to these slower adapting of species, which require more stable environments to thrive. Following the widespread KT extinction, for example, the largest surviving land vertebrate weighed only two pounds. For even a handful of these less-reproducing, large-brained, long-living organisms to have ever appeared and persisted may be at astronomical odds (remember the terrible metaphysical wager?)—and they will surely be far outlived by simpler lifeforms. The fact, therefore, that in recent ages the planet has maintained such bounties of biodiversity is something else entirely—something that would seem fit to cherish.
But just as few cereal-munchers are likely to consider the current and future well-being of the biosphere over a bowl of cornflakes, modern society seems lost to the intrinsic values of a flourishing, biodiverse world.
Biologically, a level of in-grouping, self-serving, and future-ignoring makes sense. Each and every organism, governed by the fundamental struggle to survive and reproduce, knowingly or unknowingly places themselves, their kin, and essential communities at the forefront. Squirrels are squirrel-centric; blue whales are blue whale-centric; and we, by and large, are anthropocentric. Non-humans are naturally inept at processing the short to long-term ecological impacts of their livelihoods—and humans are not equipped with very effective brain structures to that effect, either.
However, no other species has ever wrested such dominance over the web of life, itself. Earth’s biodiversity is critically threatened by the recent dominance of Homo sapiens across the planet—both an utterly unique, and deeply unfortunate position to be in.
Not too long ago, no more than twenty-thousand years, this relationship was inverted. Like a blinking newborn, anatomically modern humans entered as a complete minority in a world of incredible richness—to the extent of which no recent or future generation may ever experience again. At the time, North America was much like a “super-Serengeti” of giant ground sloths, mammoths, and many other megafauna; bison populations were estimated at 30 million; there may have been 586 million green sea turtles in the Caribbean when Europeans landed. Even today, human biomass pales in comparison to the rest of the living world: plants make up 82% of all biomass on the planet, whereas humans account for just 0.01%.
Our impact, however, astronomically exceeds our size. Non-human eradication over recent centuries has been swift and brutal, and concentrated in a blip of planetary time. Existing data is so staggering as to seem outlandish. Naming but a few points: the same biomass study finds that 83% of wild mammals have been lost since the rise of human civilization; around 85% of global fisheries are overexploited, depleted, or fully exploited; and ongoing “biological annihilation” of all types signals the sixth mass extinction of life on Earth.
In a world where ecological richness is reduced to “natural resources,” symbiotic relationships are redefined as “ecosystem services,” and interconnectedness is replaced by domination, maybe these tragic losses cannot come as a surprise.
If biodiversity offers one fundamental lesson, though, it’s that these modernized, exploitative pursuits are ultimately self-defeating. Diversity breeds resilience. Methodically culling the life-supporting systems around us saws at the very limb we sit on. Because whether recognized or not, believed or ignored, human beings have deeply innate bonds to living areas and living beings, particularly those with which we evolved. Certain cultures have long understood and acted upon this fundamental interdependence. Many Indigenous populations embody divergent ways of being from dominant, western culture which explicitly recognize humanity’s humble place in the web of life—and connection to it.
Biologist Edward O. Wilson termed this mutuality as biophilia, our oft-subconscious need to commune with those vibrant places and lifeforms which shaped both our physical and cultural evolutions. Under this umbrella, large-species interactions are believed to have particular, formative importance. Think about how enriching, even thrilling, encounters with these ever-more rare beings are: a black bear in the backcountry, dolphins in a shallow bay, even a startled deer in the park. Does it feel like a glimpse to the past, when humans weren’t widely cordoned off from, and killing en masse, our sibling species?
This is critical, but not, however, the question du jour. You haven’t forgotten our trivia, have you? Okay, good. With your answer locked in, and spotlights dimmed, the host repeats the question once more. A winner if you’re within a million, they say brightly. A long, long pause ensues, then…
On a flash of screen: 8.7 million. Were you close? Did you win?!
In the end, of course, the trivia is superficial. What matters is the reality: 8.7 million extant species on Earth (which itself is not certain—recent microbial data suggests perhaps up to one trillion!!). No matter the specifics, an incomprehensible number of unique, yet interconnected, products of endurance and chance—evolvers, adapters, survivors in a hostile universe. For life has not been, is not, and will never be a given for any actor in this 3.8 billion-year drama. As humans, to respect this tenet is perhaps to confront our mortality, fragile and special as any other being’s. And to respect Earth’s web of life is to acknowledge our enmeshing within it, to know that in a biodiverse world a single strand can never exist independent of their sum.