After the dinosaurs went extinct, why did they not return over time through evolution?

Question

I never learned much about evolution, so please do explain it like I’m 5

In: Biology

Answer 1

I can answer this (check my username).

Evolution is two things: random mutations in the gene code, coupled with heritability.

The classic example is land tortoises on the Galápagos Islands. A breeding pair reached one island and created a population.

The population spread, and some tortoises arrived on islands that required different specialisation. Luckily, not every tortoise was the same, and those that had mutations to ***fit*** their environment better survived than those that didn’t.

This is what is meant by survival of the fittest.

So now we have tortoises that are larger, smaller, longer or shorter necks, beak shape, and so on between the islands.

Now you may say that they’re still tortoises. Which is true, but it’s still evolution.

Now let’s say instead of tortoises, it was ratites, a kind of bird. As Gondwana split apart, the common ancestor of ratites had its population split between different islands, which moved so far apart for so long that no interbreeding was possible. And now we have Kiwi in New Zealand, Ostrich in Africa, Emu in Australia, and the Rhea in South America.

Back to dinosaurs, or any creature really.

A parent population of dinosaurs have offspring, some are naturally and randomly different, and if they fit their environment better they survive more. The post-Cretaceous period was very different to before, and the gene pool was both different and due to random mutations, would not be repeated. Hence, new animals and plants.

Evolution is blind. It operates one generation at a time. It is random. And all it does is select the life form that, of the population, fits the environment. If no life form does, nothing reproduces. If it fits poorly, it reproduces poorly. If it fits well, it reproduces well. The environment is constantly changing, the gene pool of available genes is constantly changing, and new mutations are constantly introduced. Some help in the moment, most do not. But evolution does not care. It just ***is***.

Further reading: The Selfish Gene, Richard Dawkins.