The Descent of Man "got right and wrong about human evolution." From natural selection to sexual selection Originally published in two volumes, The Descent of Man covered diverse aspects of animal and human animal life, ranging from comparative anatomy to mental faculties, the ability to use reason, morality, memory and imagination, or how animals choose to have sex and with whom or what. "Darwin proposed that sexual selection was instrumental in explaining the origin of what he called human 'races' and cultural progress," writes Browne. He argued that sexual selection explained why humans had broken off into different racial groups. Skin color and hair were important indicators. But according to Darwin, writes Browne, "sexual selection among humans would also affect mental traits such as intelligence and maternal love […] ."