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Charles darwin proposed the theory of evolution. And it is attributed to his book on, "on the origin of species"

Long ago all life or earth were the same species. The process of giving birth grew species.
The survival of species happened if they were fit to live and survive in the environment they lived in. For instance, the environment of a 2000BC was muscular power. You had to fight other species to live and reign. An intellectual wouldn't have survived that era. So, survival of the fittest (in that environment) comes from here.
Here comes natural selection. The feature or trait that is most dominant in the parent is transferred to the child. If the species with a dominant trait survived that environment, the trait is carried on.

It's very interesting to reason out various evolutionary traits of humans. For instance,

1. Those species without eye sight got extinct because they couldn't hunt well without sight.
2. Sex. Those animals which didn't get pleasure having sex, had lesser species of their kind. And those kinds, wouldn't have many offsprings. And due to the permutation alone, those species, or other dominant traits from those species would have gone extinct.
3. All sense organs in humans. They're so sensitive. Because of this sensitivity, we could survive those harmful environments and we could escape them.
4. A porcupine, has thorns. Those species of porcupine which didn't were killed.

But the future of evolution is going to be weird. Those people with most offsprings are going to be rich or muslims(because of their quirks). But the offsprings of the poor, I'm assuming, won't survive the harsh conditions. I'm thinking, either they'll die of diseases or they'll die of poverty.