66 million years ago, an asteroid struck the Earth. The world was plunged into darkness, killing the dinosaurs and over 90% of all species alive. Today, every living thing descends from the handful of surviving species. But not all survivors thrived.
Some animal groups, such as birds, mammals, butterflies, ants or even sunflowers and grasses, diversified, taking advantage of the devastation. Some, like crocodiles and turtles, didn’t. And still others, like multituberculate mammals and champsosaurus, survived the asteroid but went extinct in the aftermath.
So what is the difference? It might come off as a surprise, but the main factor which separated the winners from the losers, wasn’t how hard extinction hit them. It was the qualities that they possessed, that made them adaptable and prone to survival. They were fast-growing, cooperative, clever and mobile.
In some statistics, it is shown how the dominating species today, were literally on the verge of extinction. Snakes and lizards saw over 80% extinction. Mammals were hit harder, suffering 90% extinction. Perhaps three bird species survived, suggesting extinction rates of 99.9% or more. Although it seems terrible, it beats the 100% extinction rate.
By fast growing, it is implied that the species that survived had a high metabolism. After all, metabolic rate is how fast biological processes happen, allowing the species to grow and reproduce. Higher metabolism requires more food. This was initially a liability for warm-blooded birds and mammals during the impact winter, when plants couldn’t photosynthesize food. But afterwards, being able to eat, grow and breed fast let birds and mammals rapidly increase their numbers, compete effectively, and colonize new habitats. Fast-growing flowering plants, especially grasses, flourished at the expense of slower-growing species.
Lions and wolves form prides and packs to take down prey and defend territory, elephants and zebras use herds for defense. Birds flock to find food and evade predators. Ants and mound-building termites assemble vast family groups, outcompeting solitary insects. Birds, mammals and social insects also cooperate with relatives by feeding and caring for offspring, preserving their genes more efficiently.
Maybe the most remarkable trend is the rise of intelligence. Mammals and birds have the largest brains of any animals. The largest-brained mammals, the placentals, have outcompeted marsupials and egg-laying monotremes. The most diverse birds, the passerines and parrots, are the brainiest.
Among insects, the social insects – ants, bees, termites – have complex behaviors that emerge from interactions of unintelligent individuals. This phenomenon is known as swarm intelligence, and not coincidentally, these insects dominated ecosystems after the asteroid winter.
But intelligence doesn’t just make animals more competitive. It accelerates adaptation, because the first step in changing your DNA is changing your mind. For example, before mammals could evolve into whales, they first had to learn to swim and fish, only afterwards could natural selection create flippers and sonar. Before horses could evolve, their omnivorous ancestors switched to a vegan diet, then, natural selection favored tall-crowned teeth and complex guts to break down tough plants. Behavior leads, genes follow. The greater an animal’s behavioral flexibility, the more tricks it can learn, and so the greater its adaptive potential. Animals don’t consciously decide their evolutionary futures. But they do choose what to eat, how to forage or where to live.
Mobility promotes adaptability. Flight let birds, bats, butterflies and ants colonize new habitats, then diversify. Mammals, being highly mobile, quickly invade new habitats – think rabbits in Australia, or deer in New Zealand – in a way that turtles don’t. Flowering plants also evolved tricks – fruits, parachutes, burs, floating husks – to let wind, water or animals carry their seeds. It’s harder to displace competitors once they’re established, so being first into a new habitat provides a massive competitive advantage.
In conclusion, this wasn’t pure luck. When the continents divided, different animals in different parts of the world showed same patterns in survival.
Being able to learn from yesterday, process information in dreams, imagining different outcomes for tomorrow, learning and memory processing, being creative, is what allowed the species that are alive today, face unthinkable odds and survive.