Totally Human: Why We Look and Act the Way We Do by Cynthia Pratt Nicolson, illustrated by Dianne Eastman

From chapters.ca:
The fascinating science behind our bodies and behaviours and how they link us to our ancient ancestors. What makes us human is cause for surprise. We retain some of the appearances and behaviors of our very ancient ancestors, including early mammals, amphibians and fish. Yes, we look and act the way we do because of them. Totally Human explains the many puzzling and strange things about us and the weird and wonderful things we do, simply because we're human. A child-sized take on the scientific fields of evolutionary biology and psychology.