As soon as I arrived in the Indies, in the first island which I found, I took some of the natives by force, in order that they might learn and might give me information of whatever there is in these parts. And so it was that they soon understood us, and we them, either by speech or by signs, and they have been very serviceable.
Darwin theorized that mankind (both male and female) evolved alongside each other over millions of years, both reproducing after their own kind before the ability to physically have sex evolved. They did this through asexuality (without sexual desire or activity or lacking any apparent sex or sex organs). Each of them split in half: Asexual organisms reproduce by fission (splitting in half).