Sexual Dimorphism. Sexual dimorphism is the systematic difference in form between individuals of different sex in the same species. For example, in some species, including many mammals, the male is larger than the female. In others, such as some spiders, the female is larger than the male. Other sex-specific differences include color most birds , song in birds , size or presence of parts of the body used in struggles for dominance, such as horns, antlers, and tusks; size of the eyes e. Sexual dimorphism in humans is the subject of much controversy. Human male and female appearances are perceived as different, although Homo sapiens has a low level of sexual dimorphism compared with many other species.

On December 11, scientists at the University of Lethbridge in Canada published a paper revealing what appear to be sex acts between young female Japanese macaques and sika deer. The wild monkeys were observed mounting the deer in Minoo, central Japan. Similar monkey-deer interactions on Yakushima Island were reported in January But while the previous research is based on anecdotal evidence, the current work focuses on the numbers.

By Rachel Feltman December 19, There are so, so many ways in which consenting adults can conspire to get freaky without making babies. Bonobos practically build their peaceful and matriarchal society on the exchange of sexual favors.