The Descent of Man, and Selection in Relation to Sex is a book written by Charles Darwin in 1888. It explains how humans have changed over time. Darwin argued that we are not created the same way as animals, but rather we developed through a process called evolutionary change. This means that all humans can trace our roots back to a single common ancestor, and that through the years, we have gradually become the people we are today. Darwin also argued that when it comes to mating and reproduction, males and females of the same species are usually slightly different. He thought that this difference was caused by a process called selection: where the animals with better attributes were more likely to survive and reproduce. So, over time, the species would become more suited to their environment and have a better chance of surviving. This process of selection is why males and females of different species, or even humans, often look very different!