Question: Why is it that humans have smaller arms than legs, perfect for throwing stuff, but other primates don't? Why is it that humans got so prominent breasts, but other primates lesser so?

James Cole answered on 8 Jan 2019:

Thank you for this question. I think part of the answer is that our human ancestors evolved to become bipedal, so walking on two legs, and therefore did not need such long arms for quadrupedal movement (walking on all fours) like other primates do. Furthermore, by walking on two legs we stopped using our arms to move through the trees of forests, we effectively had no use for long arms to support this type of locomotion as we became more bipedal so you can see through the human fossil record that once our ancestors became fully bipedal around 2 million years ago, arm length shortened because we were using our arms and hands in a different way to other primates (to make tools etc).

In terms of human breasts, I’m not entirely sure, but this video may help: https://www.businessinsider.com/why-are-human-breasts-big-2018-2?r=US&IR=T