As a paraphilia, breast fetishism (also known as mastofact, breast partialism, or mazophilia) is a highly atypical sexual interest consisting of an exclusive focus on female breasts, which is a type of partialism. The term breast fetishism is also used in the non-paraphilic sense, to refer to cultural attention to female breasts and the sexuality they represent. Scientists hypothesize that non-paraphilic sexual attraction to breasts is the result of their function as a secondary sex characteristic. The breasts play roles in both sexual pleasure and reproduction. Some authors have discussed the modern widespread fascination with breasts among heterosexual males in Western societies, especially in the United States, within the context of sexual fetishism. Scientific explanation Scientists hypothesize that non-paraphilic sexual attraction to breasts is the result of their function as a secondary sex characteristic. The breasts play roles in both sexual pleasure and reproduction. Men typically find female breasts attractive and this holds true for a variety of cultures. Zoologist and ethologist Desmond Morris theorizes that cleavage is a sexual signal that imitates the image of the cleft between the buttocks, which according to Morris in The Naked Ape is also unique to humans, other primates as a rule having much flatter buttocks. Evolutionary psychologists theorize that humans' permanently enlarged breasts, in contrast to other primates' breasts, which only enlarge during ovulation, allows human females to "solicit [human] male attention and investment even when they are not really fertile". Sexual attraction to breasts is considered normal unless it is exclusive and is therefore a form of partialism. Society and culture General There is a widespread fascination with women's breasts, and especially their size. Many people, both male and female, consider breasts an important female secondary sex characteristic. Modern female fashions which focus on tight clothing and the display of cleavage have been attributed to an increase in breast fetishism. Display of cleavage with a low neckline is often regarded as a form of feminine flirting or seduction, as well as aesthetic or erotic. Most heterosexual men derive erotic pleasure from seeing a woman's breasts, and some people derive pleasure in their female partner exposing cleavage. When cleavage is enhanced with a push-up bra or exposed by a low neckline it may draw attention. There are differences of opinion as to how much cleavage exposure is acceptable in public. The extent to which a woman may expose her breasts depends on