Scientifically Speaking | What will life be like after humans are extinct?
What will life in a post-human world look like? We can never know for sure, but we can make specific predictions based on our knowledge of existing life. That is what ecologist Rob Dunn set out to do in his latest book
Modern humans have been around 200,000 years, which is a fraction of the nearly four billion years that life has survived on earth. Ask a biologist what the future of our species is on the planet, and you will hear that we’re headed for extinction sooner or later. In that sense, we’re no different from any other form of life.
Human activities in the Anthropocene are leading to the sixth mass extinction event. (Shutterstock)
Human activities in the Anthropocene are leading to the sixth mass extinction event. Duke University biologist Stuart Pimm estimates that species on the planet are dying at a rate that is one thousand times faster than new ones are evolving. In other words, due to human activities, the earth is witnessing catastrophic biodiversity loss. And the climate crisis threatens to exacerbate this great dying.
Most of the life on the planet has not been identified and perhaps will never be studied by humans. For example, we don’t even have a grasp of how many species of insects there are on the planet. As many as seven out of eight species of insects might not have been observed or named.
Our species might be the last line of humans. Or it might evolve into something that is not quite the same as the humans of today. Yet, life will persist beyond humans. This is inevitable, according to the laws of evolution as documented in the natural history of the planet. But even though the climate crisis is in focus for us now and (if unchecked) will cause hardships to hundreds of millions, it might not rise to the level of an extinction-level event for humans. No one knows when and how humans will become extinct.
The thought of the extinction of our species may be morbid, but we are the only species that can think about our fate. It is an area of fertile thought for a biologist.
What will life in a post-human world look like? We can never know for sure, but we can make specific predictions based on our knowledge of existing life. That is exactly what ecologist Rob Dunn set out to do in his latest book, A Natural History of the Future: What the Laws of Biology Tell Us About the Destiny of the Human Species. As the author notes, we cannot control how species evolve in accordance with our behaviours. The rise of the Sars-CoV-2 variants is a case in point. But the species that evolve with us and after us also obey biological principles
Evolution is all around us – even in urban environments. If some habitats are shrinking, then others are growing. Some of the most successful crop plants and animals have been selected for specific traits. And many species have opportunistically evolved with us. The biomass of cities mainly consists of humans, pets, pests, and our collective food and waste.
Dunn notes that humans are hosts to thousands of species – perhaps more than on any other form of life on the planet. It is quite possible that some of these species, and some domestic pets and crop plants, will become extinct once humans are not around to take care of them. And parasites that depend on humans that cannot evolve to find other species will also become extinct.
All forms of life will be affected by the climate crisis, but not equally. Plants will thrive in parts of the planet that were once covered in ice and increases in carbon dioxide may lead to lush growth of certain plants.
Dunn writes that “if we disappear during warmer times, many species, particularly mammal species, may evolve smaller body sizes. The evolution of small-bodies mammals is well documented during the last period in which Earth was extremely hot. Tiny horses evolved.”
After every mass extinction event, there is a rebirth. Even after human extinction, there will be a resurgence of new forms of life. There will be some animals and plants that fill in existing niches – flying birds and mammalian carnivores for example. But there will also be some animals that we cannot predict because they are so specifically unusual. The biologist Stephen Jay Gould predicted that humans were one such animal: If you rolled the tape of life back you would not get humans again.
If all large mammals become extinct, then smaller mammals such as rodents may diversify into new species to fill ecological niches. This happened once before with the extinction of non-bird dinosaurs 66 million years ago, and it may happen again after humans are gone. For example, rats that do not rely on humans could evolve to climb trees, take to the sky, and roam grasslands.
On the one hand, it’s possible to predict that the forms of life after we are gone will depend on the state of the Earth when we become extinct. But on the other, the forces of nature might tilt the planet back slowly to a greener and more entropic state. And as a microbiologist, I appreciate that the vast diversity of life both in terms of the earth’s past and future (up until the moment the sun causes the earth to become inhospitable for all forms of life in the distant future) will remain microbial.
Microbes have always been the predominant form of life on the planet and there are more microbes in our bodies than there are human cells. Environments that are inhospitable to us are also breeding grounds for forms of life –hydrothermal vents deep in the sea, oxygen-deprived regions of the earth, subsurface ice – all of them harbour myriad forms of life, many of which we may never know. This should give us hope that even after human extinction, many new species will rise. Only we will not be around to see them.
Anirban Mahapatra is a scientist by training and the author of a book on COVID-19. He’s writing a second popular-science book
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