A biological exuberance ! 

 Animal homosexuality has mostly been regarded as a taboo topic or at least, as curious or abnormal events from a conventional standpoint. Nevertheless, numerous recent studies have revealed a growing evidence for homosexual behaviours. Neo-Darwinism longtime alleged that male homosexual behaviours chiefly result from the sexual frustration of bachelor males or revealed abnormal behaviours.

 In fact, evolution theory predicts that the occurrence of non-adaptive behaviours (i.e. behaviours with no reproductive effects) must decrease in a population but homosexuality has been found as casual activities in numerous species. Thus, new theories tried to explain such a behavior :

1. The aggression hypothesis argued that homosexual interactions resulted from frustration of bachelors.

2. Same-sex interactions could have a social sexual role in dominance.

3. Homosexuality could result from scarcity of sexual partners

4. Homosexuality was thought as having a training function initiating future sexual performances (training hypothesis)

5. homosexual behaviours should be regarded as cooperative either by maintaining pair bonds in birds dominance hierarchy/cooperation

6. Regulation of population dynamics

7. according to the sneaky male theory, a male may gain some access to females by being tolerated by another dominant male

8. Homosexuality may result from a biased sex-ratio

9.  it could be also argued that homosexuality is a part of the natural repertoire of sexual behaviour

 Actually, deliberate exclusive homosexuality in a solitary species such as the European polecat Mustela putorius (free choice hypothesis, Lodé 2006) apparently serves no adaptive function. Deliberate homosexual behaviour was never documented in other non-social and non-cooperative species, competing for mates and thus addresses crucial evolutionary issues.

in Th Lodé - La GUERRE DES SEXES (2006) Eds Odile Jacob .