Steller’s sea cow. The dodo. Passenger pigeons.
These are names many of us have heard. They’re part of a sad list, now dozens of species long, of animals that human activity has driven extinct in recent history. Many other members of this list — the quagga; the Tasmanian tiger; the golden toad — are less well known, either because they lacked the charisma to become the stuff of legend, or because they have already faded from our collective memories.
Hundreds of other plants and animals perch precariously on other lists. They are “endangered,” “red-listed,” “threatened”: all in all, they’re likely to go extinct soon enough, leaving behind only photos, videos and perhaps a test tube of DNA in the back of a conservation biologist’s freezer.
Extinction events themselves are hardly a rarity: almost all species that have lived on Earth have gone extinct. As the world changes and new species evolve, some of these species invariably fall behind in the race of natural selection. Evidence from the fossil record suggests that, on average, 1-5 species go extinct each year. But sometimes, extinction rates spike, with many hundreds, or even thousands, of species dying out at once. Today, these extinctions are happening at an unprecedented rate.
We call synchronized events “mass extinctions.” From what we can learn of the fossil record, there have been at least five mass extinctions in Earth’s history. The most recent occurred 65 million years ago and wiped out the dinosaurs. Each of these events occurred long before our species evolved. We have no idea what these mass extinctions were like, what caused them and what their effects were on the living ecosystems at the time.
But now, we’re about to find out. We are in the midst of the sixth mass extinction — and this time, we know the cause: human activity.
The human population is booming. In the time it takes you to read this column (say, fifteen minutes) 3,500 babies will have been born. Today, the global population stands at 7.2 billion, and growing.
As our population grows, so too does our impact on the planet. We each need space to live and work, farmland to grow our food and maybe even some room to play. The amount of technology that we use affects the scale of these impacts: Picture the difference between a city and a village, or between an industrial-strength farming operation and a small, carbon-neutral vineyard.
Today, our impact on the planet has become so profound that it will be recorded in the geological record. Scientists call this time period the “Anthropocene,” the time in which human activity has become a driving force in nature, affecting everything from the carbon cycle to the climate.
Not only are we dramatically changing the planet, we are also homogenizing it — which is why, in the last few years, a new term has come into vogue: “Homogocene.” From the way we construct our homes, to our preference for a few key food crops, to our ability to transport goods (and inadvertent hangers-on) around the world in a matter of hours, we are turning the planet into a giant human playground.
On the one hand, this is necessary. For example, we cannot hope to feed 7 billion people without high-intensity agriculture. But on the other hand, our doing so has severe consequences for other life on the planet. Many, many species that cannot survive in human-dominated landscapes will be increasingly squeezed into tiny scraps of “preserved” land. Most are unlikely to survive this transition — and it’s the start of these extinctions that have catapulted us into the sixth mass extinction.
But this story is not entirely a tragedy. Yes, some charismatic and cuddly mammals may go, literally, “the way of the dodo.” But plenty of species will thrive in the ecological opportunities created by the Homogocene.
For example, we’d be hard-pressed to find a better success story than the corn plant, once a humble grass that now covers 30 percent of American farmland. And many of our most despised “pest” species are only known as such because they’re thriving in man-made environments. House mice, cockroaches, even dandelions and deer: these species have found ways to make a living in and around human habitation.
Meanwhile, evolution carries on, providing living organisms with the chance to adapt to human-dominated systems. From bacteria that can consume oil to fungi that can degrade plastic, we will continue to observe new life forms and patterns shaped by our influence.
Historically, mass extinctions often precede explosions of diversification, as the surviving organisms spread out to fill in the gaps. (For example, the dino die-off likely made room for our mammalian ancestors to spread, diversify and eventually give rise to us.) What will follow the sixth mass extinction remains to be seen.
Contact Holly Moeller at [email protected].