Before this fact being acknowledged by a modern scientific community, a lot of men of science have written about their observations. This comes only to confirm the saying that all new is well-forgotten old. The detail that old men have managed to reach is amazing. They went as far as recognizing apes as our closest relatives.
The first source that came into my sight to support all this is interestingly enough of Arabic origin, The Muqaddimah. Here's an excerpt:
This is the case with the simple material elements; it is the case with palms and vines, (which constitute) the last stage of plants, in their relation to snails and shellfish, (which constitute) the (lowest) stage of animals. It is also the case with monkeys, creatures combining in themselves cleverness and perception, in their relation to man, the being who has the ability to think and to reflect. (http://en.wikipedia.org/wiki/Muqaddimah#Biology)A quick search on Wikipedia will get you to an article with a History of evolutionary thought. So we currently know that as far as Anaximander of Miletus (c. 610 – c. 546 BC) goes, there has been something close to evolutionary thought. I hope we find even older sources but even this is enough to see the emergence of thinking, free of the supernatural in relation to human beings.