ScienceDaily: In several species of primates, males often discern when to mate with a female based on cyclical changes in the size and firmness of her sexual swelling -- a visual signal of a female's probability to conceive. Primatologists have now investigated for the first time the relationship between ovarian hormones and sexual swellings in wild female bonobos. The likelihood that a female bonobo ovulates during her maximum swelling phase is much lower than in the closely related chimpanzees. Swellings are...