Massive extinctions have made life on Earth more diverse – and could still

Over the last fifty years, Earth has been hit repeatedly by massive extinctions, destroying most of the planet's species. And each time, life began again and ended up diversifying.

Is life incredibly resilient or is there anything else? Could massive extinctions really help life to diversify and succeed – and if so, how? Given that we are currently facing another extinction event, it is very urgent to try to determine how massive extinctions affect diversity.

Mass extinction is probably the most striking motif in the fossil record. Many species – even whole families – are rapidly disappearing simultaneously around the world. An extinction of this magnitude usually requires a kind of global environmental disaster, so severe and so rapid that species can not evolve but rather disappear.

Massive volcanic eruptions led to extinctions in the late Devonian, Permian and Triassic periods. Global cooling and intense glaciation resulted in Ordivician-Silurian extinctions. An asteroid caused the extinction of dinosaurs at the end of the Cretaceous. These "Big Five" extinctions attract the most attention because they are the most important. But many less important events, but still threatening for civilization, have also occurred, such as the pulse of extinction before the final Permian event.

These events were indescribably destructive. The impact of the asteroid Chicxulub that ended the Cretaceous period has blocked photosynthesis for years and caused decades of global cooling. Anything that could not protect itself from the cold, or find food in the dark – which was most of the species – perished. Perhaps 90% of all species have disappeared in just a few years.

But life has resumed and the recovery has been rapid. 90% of the mammalian species were eliminated by the asteroid, but they recovered within 300 000 years, before becoming horses, whales, bats and our primate ancestors. Birds and fish experienced similar recovery and radiation. And many other organisms – snakes, tuna and swordfish, butterflies and ants, grasses, orchids and asters – have evolved or diversified at the same time.

This pattern of recovery and diversification emerged after each mass extinction. The extinction of the final Permian saw the mammal-like species take a hit, but reptiles thrived afterwards. After the reptiles suffered at the end of the Triassic, the surviving dinosaurs invaded the planet and diversified. Although a mass extinction has ended the dinosaurs, they first evolved only by mass extinction.

Despite this chaos, life has slowly diversified over the past 500 years. In fact, several elements suggest that extinction is driving this increased diversity. On the one hand, the fastest growing periods of diversity occur immediately after massive extinctions. But perhaps most strikingly, recovery is not solely motivated by an increase in the number of species.

In times of recovery, animals innovate – find new ways to make a living. They exploit new habitats, new foods, new means of locomotion. For example, our fish-like ancestors crawled for the first time on the earth after the end of the Devonian's extinction.

Evolutionary innovation

Extinction does not only lead to this process of speciation. It also promotes evolutionary innovation. It is no coincidence that the greatest impulse for innovation in the history of life – the evolution of complex animals in the Cambrian explosion – occurred after the extinction of the Ediacarian animals that preceded them. .

Innovation can increase the number of species that can coexist because it allows species to settle in new niches instead of fighting for old ones. The fish crawling on the mainland did not compete with the fish of the seas. Bats hunting at night with sonar did not compete with active birds during the day. Innovation means that evolution is not a zero sum game. The species can diversify without causing the extinction of others. But why is extinction an engine of innovation?

Stable ecosystems can prevent innovation. A modern wolf is probably a much more dangerous predator than a velociraptor, but a tiny mammal could not turn into a Cretaceous wolf because there were velociraptors. All the experiments on carnivores would have ended badly, the poorly adapted mammal competing – or simply eaten – with the already well adapted mammal Velociraptor.

But, in the lulls after extinction, the evolution can allow to experiment conceptions initially badly adapted, but presenting a long-term potential. The stars of the series having disappeared, the doubled of evolution have the chance to prove themselves.

The extinction of Velociraptor gave mammals the freedom to experiment with new niches. At first, they were ill equipped for a predatory lifestyle, but without the dinosaurs competing with them, they did not have to be terribly good at surviving. They needed only to be as good as the other things at the time. So they thrived in an ecological vacuum, eventually becoming fast and smart big pack hunters.

Creative destruction

Life is not only resilient, it feeds on adversity. Life will even recover from the wave of man-made extinctions. If we disappear tomorrow, the species would evolve to replace the woolly mammoths, the sleeping birds and the traveling pigeon, and life would probably become even more diverse than before. This does not justify complacency. It will not happen in our lifetime, or even in our life, but in millions of years.

This idea that extinction is the engine of innovation can even apply to human history. The extinction of the megafauna of the Ice Age surely decimated the hunter-gatherer groups, but it may have also given agriculture a chance to develop. The Black Death has caused untold human suffering, but the transformation of political and economic systems may have led to the Renaissance.

Economists talk about creative destruction, the idea that creating a new order means destroying the old. But evolution suggests that there is another type of creative destruction, the destruction of the old system creating a vacuum and resulting in the creation of something new and often better. When things go wrong, it's precisely when the opportunity is greatest.