User:Ollie Shannon Evo-Anthro/sandbox

= Evolution of Same-Sex Sexual Behavior = Same-sex sexual behavior in animals falls into 5 categories enumerated by the linguist and biologist Bruce Bagemihl These categories include courting, affection, genital, sexual, pair-bonding and parenting behaviors. These categories cover the ways that animals can engage in sexual behavior with another. Literature published on non-human animals that engage in same-sex sexual behavior is extensive, including 450 documented species. The 450 species exist in a variety of environments, breeding systems, and taxa in both wild and captive populations. In humans same-sex sexual behavior has been documented across history and has existed in many human cultures. The propensity of an individual to engage in same-sex sexual behavior is an inherited trait. Many researchers see the continuation of same-sex sexual behavior within populations as an evolutionary paradox, how could a trait evolve and continue through generations that directly and negatively impacted the fitness of an organism that expresses that trait        ?

Types of Questions or Hypotheses
Tinbergen suggested asking 2 types of questions may help people more fully understand behavior: ultimate questions that ask why?, and proximate questions, that ask how?. Using these two types of questions one can investigate behavior through different lenses and therefore, have different answer

Mating rehearsal Hypothesis
Through rehearsing mating with members of the same sex, individuals have a greater chance of females accepting their mating advances and less mistakes in the mating process. Studies in Drosphila Melanogaste r support this theory; immature males who are courted by mature males have a higher success rate and speed of copulation with females at maturity.

Indirect Sperm Transfer hypothesis
When engaging in male-male sexual behavior, males deposit spermatophores, and these spermatophores may indirectly fertilize a female with subsequent male-female mating. Indirect insemination was hypothesized and tested in Tirbolium casaneum flour beetles. Male flour beetles commonly mount each other and produce spermatophores. Levan et al tested if the spermatophores were then transferred to females during subsequent copulation and resulted in fertilization. They found limited evidence to support that transferred sperm resulted in fertilization in subsequent male to female mating. From their findings they propose a new hypothesis that male male mating may allow males to deposit older less viable spermatophores on their male partners, through this they ae able to deposit the newest and most viable sperm on female partners.

Social Selection or Sociosexual hypothesis
Same-sex sexual behavior confers social rather than reproductive benefits. This hypothesis was first suggested by Kirkpatrick in 2000. This Theory focuses on humans, hominids and non-human primates, in this literature he suggests that same-sex sexual behavior may play a social role supporting same sex alliances; aiding in cooperation and defense of common resources. Same-sex sexual behavior may not be a reproductive strategy but a social survival strategy. Reproductive strategy includes adaptations that increase the reproductive fitness of an individual, survival strategies increase the survival of the individual .Kirkpatrick notes that culture is a factor in the expression of same-sex behavior; the expression of same-sex sexual behavior is more likely to occur in societies where social power is derived from social networks rather than individuals. Early hominids may have been socially broken up into same sex groups as we see in many primates today; survival depended on being integrated to a social group; those who had close social bonds with a greater number of individuals across the sexes may have survived at a higher rate. Same-sex sexual behavior need not always include explicit sexual behavior between individuals throughout their lifetime. Bisexuality is more common than exclusive homosexuals behavior across one's life in humans and other animals. Explicit same sex sexual behavior in adolescence may lead to an enduring social bond and closeness between the individuals. In bonobos same-sex sexual behavior is integral in the exchange network for food sharing. Same-sex sexual behavior is shown to be flexible and shift throughout a person’s life, and the shift to same-sex sexual behavior may occur when social bonds are more important than sexual reproduction. Same sex behavior may occur in birthing parents post reproduction as a need to secure resources for offspring. Sexual behavior between different sexes as well as same sex when serving a social role the sex of the participants is less important than the social need the act fulfills .Self domestication of humans may have led to greater selection of same-sex sexual behavior as the traits of domestication include traits that lead to prosociality; these include reduced threat and aggression responses and increased social communication and play ability.

Ancestral Indiscriminate Mating hypothesis
The ancestral mating system included both same-sex sexual behavior and different sex sexual behavior. Same-sex sexual behavior is very common in sexual reproducing species. Instead of looking to explain same-sex sexual behavior as having a different origin than different sex sexual behavior both are ancestral traits. This shift in perspective can bring into question the pillars of which prior investigation into the evolutionary explanations of same-sex sexual behavior rest. If, indiscriminate mating is an ancestral trait, then, scientists can turn their focus onto how same-sex sexual behavior may shift with shifting ecology, evolutionary history and development.

Inclusive Fitness
Inclusive fitness theory suggests that the fitness cost to an individual that does not reproduce, but instead lends their resources to those who are closely related to them, often nieces and nephews, is lower than the increase to their inclusive fitness. Hamilton’s rule ( rb-c > 0) states that the r ( relatedness of the individual) times b(the reproductive benefit) minus c( the cost of the altruistic act) must be greater than 0. This theory has rarely been supported when data include those who engage exclusively in same-sex sexual behavior.

Pleiotropic hypothesis
Hypnotize that sexual behavior is linked to pleiotropic genes. In opposite sex twins the inheritance of the same genes will predispose one twin to engage in same sex sexual behavior and will positively impact the number of opposite sex sexual partners in the twin of the opposite sex. Their study found tentative evidence to support this hypothesis in their study that included 1907 twin pairs.

Infection hypothesis
Through epigenetics pathogens may activate genes that control the desire for same-sex sexual attraction. This theory has been supported by any research.

Mal-adaption Hypothesis
Same-sex sexual behavior is more likely to occur when the organism is mal adapted to their environment. This may be why the occurrence of same-sex sexual behavior increases in captive species, because that species is not adapted to their current environment their ability to correctly identify mates may decline.