another good question. Here’s a great stat coutesy of Richard Dawkins:
If you took a phtograph of yourself and placed it on the floor, then took a photograph of your mum and placed it on top of the first photo, then placed a photo of your grandad on top of that and so on…
By the time had a pile of photographs 400 times the height of a New York skyscraper, you would have a photo of a fish.
If we kept going, the photos of the fish would become less developed life forms. The really fascinating thing is that if you were to compare each of these pics to the one directly before and after it, they would look like the same species. Evolution is such a slow process, but a huge one.