Prostitution among animals

Prostitution among animals is the phenomenon in which non-human animals practice transactional sex. This was first noted in 1998 among female Adélie penguins trading stones for sex during a shortage of stones. Transactional sex has also been noted in various species of primates, including chimpanzees.

Penguins
Prostitution in animals was first reported in 1998 by Fiona Hunter, a researcher at the University of Cambridge, and Lloyd Davis of University of Otago, who had spent five years observing the mating behavior of Adélie penguins. The study was conducted as part of an Antarctica New Zealand program on Ross Island, approximately 800 mi from the South Pole. According to the paper, titled Female Adélie Penguins Acquire Nest Material from Extrapair Males after Engaging in Extrapair Copulations, extra-pair copulation occurs at the male's nesting site, after which the female takes one or more stones. In contrast, when extra-pair copulation occurs at the female's nesting site, the male never takes a stone. A male who has copulated with a female benefits his progeny when she takes a stone. Sometimes copulation does not occur, but the female still takes a stone. Both males and females steal stones; sometimes they are successful, but at other times, they are attacked. The female is not always willing to copulate to avoid a fight. The researchers speculated about the possible genetic fitness advantages and disadvantages of the practice, and were not sure that the female copulates mainly in order to obtain a stone.

Hunter subsequently said that the female penguins probably did not engage in prostitution only for stones. She said: "... what they are doing is having copulation for another reason and just taking the stones as well. We don't know exactly why, but they are using the males." This behavior was also suggested as a mate choice process by which the females might find a possible future mate. This would provide a female penguin with another male penguin should their current mate die. According to Hunter's observation, the number of prostitute penguins was "only a few percent."

Chimpanzees
A study conducted by the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and published online in the Public Library of Science attempted to support the meat-for-sex behavior hypothesis, according to which the best male hunters in early human societies had the maximum number of sexual partners. Unable to study early humans, researchers studied chimpanzees. Researchers observed chimpanzees in Taï National Park and concluded that a form of prostitution exists among the chimpanzees in which females offer sex to males in exchange for meat. According to Cristina Gomes of the Institute, the study "strongly suggests that wild chimpanzees exchange meat for sex and do so on a long-term basis". The data reveal that chimps enter into communities of hunting and sharing meat with each other over long periods of time, and that females within the meat-sharing community tend to copulate with males of their own meat-sharing community. Direct exchange of meat for sex has not been observed.

Capuchin monkeys
A study at Yale–New Haven Hospital trained capuchin monkeys to use silver discs as money in order to study their economic behavior. The discs could be exchanged by the monkeys for various treats. During one isolated incident, a researcher observed what appeared to be a monkey exchanging a disc for sex. The monkey that was paid for sex immediately traded the silver disc for a grape.