Sociobiological theories of rape explore how evolutionary adaptation influences the psychology of rapists. Such theories are highly controversial, as traditional theories typically do not consider rape a behavioral adaptation. Some object to such theories on ethical, religious, political, or scientific grounds. Others argue correct knowledge of rape causes is necessary for effective preventive measures. A Natural History of Rape The idea that rape evolved under some circumstances as a genetically advantageous behavioral adaptation was popularized by biologist Randy Thornhill and anthropologist Craig T. Palmer in their book A Natural History of Rape (2000). Animal coercive sex Behavior resembling rape in humans can be seen in the animal kingdom, including ducks and geese, bottlenose dolphins, and chimpanzees. Indeed, in orangutans, close human relatives, such copulations constitute up to half of observed matings. Such 'forced copulations' involve animals being approached and sexually penetrated while struggling or attempting to escape. Observations of forced sex in animals are uncontroversial; controversial are the interpretation of these observations and the extension of theories based on them to humans. "Thornhill introduces this theory by describing the sexual behavior of scorpionflies. In which the male may gain sex from the female either by presenting a gift of food during courtship or without a nuptial offering, in which case force is necessary to restrain her." Human rape Rape is hypothetically homologous to similar behavior in animals. "Human rape appears not as an aberration but as an alternative gene-promotion strategy that is most likely to be adopted by the 'losers' in the competitive, harem-building struggle. If the means of access to legitimate, consenting sex is not available, then a male may be faced with the choice between force or genetic extinction." Thornhill and Palmer write that "In short, a man can have many children, with little inconvenience to himself; a woman can have only a few, and with great effort." Females thus tend toward selectivity with sexual partners. Rape could be a reproductive strategy for males. They point to several other factors indicating that rape may be a reproductive strategy. Most rapes occur during prime childbearing years. Rapists usually use no more force than necessary to subdue, argued to be since physically injuring victims would harm reproduction. Moreover, "In many cultures rape is treated as a crime against the victim's husband." Anthropologist Edward H. Hagen states in his Evolutionary Psychology FAQ from 2002 that he believes there is no clear