Surprisingly, the fact – it was mass extinctions that made life on Earth more diverse
Over the past half billion years, the Earth has undergone mass extinction over and over again, destroying most species on the planet. And each time, life was restored and ultimately continued to become more and more diverse.
Is it just that life is incredibly stable, or is it something else? Can mass extinctions really help life diversify and succeed – and if so, how? Given that we are currently facing a completely new type of extinction, which we ourselves provoked, there is a special need to try to find out how mass extinctions affect the diversity of species on the planet.
Mass extinction is probably the most striking picture in the fossil record. A huge number of species – even entire families – in the blink of an eye (by geological standards, of course) disappear simultaneously around the world. Extinction on such a scale usually requires some kind of global environmental disaster, so serious and so fast that the species simply do not have time to evolve, and instead disappear.
Catastrophic volcanic eruptions are a major factor in mass extinctions.
Intense volcanic eruptions throughout the Earth led to mass extinctions at the end of the Devonian, Perm and Triassic periods. Global cooling and intense glaciation led to the Ordovician-Silurian extinction. The asteroid caused the extinction of dinosaurs at the end of the Cretaceous. This "big five" extinctions attract the most attention, because they are obviously the most global. But also there were many less significant, but still life-threatening extinctions on the planet, such as, for example, the Eocene-Oligocene, which occurred relatively recently, about 37-34 million years ago: then 15% of all genera died and the composition of mammals in the territory changed dramatically Of Europe.
These events were indescribably destructive. The collision of the asteroid Chiksulub with the Earth, which ended the Cretaceous period, stopped photosynthesis for years and caused decades of global cooling. All living things that could not hide from the cold or find food in the dark – and this was the majority of species – perished. Perhaps 90% of all species have disappeared in just a few years.
But life managed to bounce back, and the "recovery" was quick. 90% of the species of mammals were destroyed by an asteroid, but they recovered, and then some within literally a couple of hundreds of thousands of years evolved into horses, whales, bats and our primates. Birds and fish experienced an equally rapid recovery and alteration. New species of snakes, butterflies, ants, orchids and asters appeared – a real explosion of life.
Butterflies began to develop actively after the Cretaceous extinction.
This model of recovery and development occurred after each mass extinction. At the end of the Permian extinction, the simplest mammals seem to have received a blow under the breath, but reptiles blossomed in lush color. After the number of reptiles sharply decreased due to extinction at the end of the Triassic, the surviving dinosaurs captured the planet and created many new species. And although the mass extinction at the end of the Cretaceous period put an end to them, it should be remembered that once they evolved only due to such a cataclysm.
Despite all this chaos, life has become more and more diverse over the past 500 million years. In fact, a few things directly hint that extinction leads to increased diversity. At a minimum, the fastest periods of increased diversity occur immediately after mass extinction. But, even more strikingly, the restoration is not only due to an increase in the number of species.
In the process of recovery, animals evolve – they find new ways to survive in changing conditions. They master new habitats, new food, new ways of transportation. For example, our fish-like ancestors first crawled out to land after the end of the Devonian extinction, because there was nothing to eat in moraines.
Extinction not only stimulates the process of speciation. They also drive evolutionary innovation. It is no accident that the biggest impulse of innovations in the history of life – the evolution of complex animals during the so-called Cambrian explosion – occurred after the extinction of the ediac animals that inhabited the Earth before them.
Innovation can increase the number of species that can coexist peacefully, because they allow emerging species to move into new niches, rather than fight for old ones. Fish that crawled onto land and sprouted legs no longer competed for food with fish in the seas. Bats hunting at night with sonar did not compete with birds that were active during the day. Innovation means evolution is a game with a nonzero sum. Species can become more diverse without forcing others to die out. But why, then, is extinction leading to innovation?
More than a thousand species of bats developed without competition with birds.
Stable ecosystems actively discourage innovation. The modern wolf is probably a much more dangerous predator than the velociraptor, but the tiny mammal could not turn into a wolf in the Cretaceous, because there were velociraptors. Any experiments would end badly: a poorly adapted mammal would compete with an already well-adapted velociraptor and, most likely, in the end it would simply be eaten by it.
But, in periods of calm after extinctions, evolution can experiment with solutions that were initially poorly adapted to harsh life, but had long-term potential. With the disappearance of the "stars of the show", evolutionary "understudies" get a chance to prove themselves.
The extinction of carnivorous dinosaurs gave mammals the freedom to experiment with new niches. Initially, they were poorly adapted to a predatory lifestyle, but without dinosaurs competing with them or eating them, they did not need to be excellent hunters in order to survive. They just had to be no worse than other species at that time. In this way, they thrived in an ecological vacuum, eventually turning into large, fast and intelligent flocking predators.
Life is not just sustainable, it thrives on adversity. She will recover easily after the current wave of extinctions caused by man. If we disappear tomorrow, species will evolve to replace woolly mammoths, dodo birds, and wandering pigeons. Moreover, life is likely to become even more diverse than before. However, do not reassure yourself. This will not happen during our lives, and not even during the life of our species, but after millions of years.
Dodo bird: lived quietly in Mauritius until the hungry sailors got there. After that, it was quickly destroyed and remained only in the form of drawings and stuffed animals.
This idea that extinction leads to innovation can even be applied to human history. The disappearance of the megafauna of the ice age was supposed to destroy the groups of hunter-gatherers, but it could also give a chance to the development of agriculture. The black death destroyed up to 3/4 of the inhabitants of medieval Europe, but the political and economic turmoil that it brought 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 kind of creative destruction, when the collapse of the old system creates a vacuum and actually leads to the creation of something new and often better. When things get worse, this is exactly the period when an excellent opportunity arises to become better.