I never learned much about evolution, so please do explain it like I’m 5
In: Biology
No one can truly know why. Evolution is a relatively random process based on external pressures. Evolution will try to make changes to the genome based on the environment. Sometimes those changes go well, sometimes they go bad. The bad ones are discarded, the good ones are kept. That’s the general idea.
Not all the dinosaurs went extinct, though most did. All living creatures are descended from animals that survived the asteroid impact. Funnily enough, chickens seem to be descended from the Tyrannosaurus Rex. The big apex predator got nuked into a chicken.
The reason why dinosaurs didn’t “come back”, as we like to think of it, is partly because of something called convergent evolution. Convergent evolution is when two unrelated species evolve into the same creature (traits, looks etc.). A famous example of this are the evolution of wings in bats and birds. Bats and birds are unrelated to each other, but they both evolved wings because the environment they evolved in helped push in a direction where wings are very useful for the survival of the species. The likelihood of convergent evolution, at least to the degree of the Tyrannosaurus Rex coming back, is astronomically unlikely, largely because the asteroid impact changed the environment to such a degree where the same pressures didn’t exist anymore. The dinosaurs that survived both the impact and the massive environmental changes (check out nuclear winter) ended up dying out or migrated to other areas where they inevitably died out or evolution continued in a different environment that had different requirements and needs to survive.
Convergent evolution is usually only observed in small parts and traits, like the example of wings in both bats and birds, but entire species is practically impossible. Not entirely impossible, just so unlikely that it’s *practically* impossible.
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