Now I just learn that estrus is a trait in all mammals except Humans. So does it occur significantly in Humans? Of course I'm aware of the cliched "horny", "aroused" etc., but is it a biological function in Humans too? and if so, when and what is it called?
By 'human estrus', I take it to mean that the female shows some increased desire when they are fertile.
At the height of fertility, which coincides with estrus, female behavior changes a stronger interest in sexual activity is exhibited. In many primates in general, the female may give of a strong scent or even physically show color or swelling that indicates even to observers of other species that they are fertile, also engendering sexual behavior in the males.
For instance, baboons are well known for reddening of the female's rump and they also emit a strong scent. Non - primates also show estrus - most of us know how dogs and cats can change their behavior.
Human signs of Estrus is of great interest to primatologists, evolutionary biologists and psychologists as it influences the biology and the social nature of people. It has been proposed that humans do not exhibit estrus and this is still an influential idea. Certainly its difficult to look at a woman and tell whether she is ovulating and most women themselves cannot tell when that is happening.
Still, examination of behavior and appearance have shown that womens appearance does change over their monthly fertility cycle. Women's faces may become thinner at higher fertility and this and other cues make them more desirable on the average. While their sexual desire is not clearly higher, female perception of men's faces changes too.
While this is quite different than the typical definition of estrus, the biochemical cycle of fertility does affect human social behavior and preferences, perceptions. The evolutionary reasons for these changes are probably adapted to the highly social nature of human existence and the fact that offspring are such a large investment.