Why does homosexuality exist among mammals?

Homosexuality is a phenomenon observed in more than 1,500 species of animals, including mammals. But what evolutionary benefits does this behavior have? 

What biological and environmental factors influence it? In this article, we will try to answer these questions from a scientific perspective.

Why does homosexuality exist among mammals?

1. What is homosexuality?

Homosexuality is defined as sexual attraction or sexual behavior between individuals of the same sex or gender. However, this definition may be limited, as it does not encompass the diversity of ways in which animals express their sexuality. For example, some animals may have homosexual and heterosexual relationships throughout their lives, while others may change preferences depending on environmental or social conditions. 

Furthermore, animal sexuality is not limited to the reproductive act, but also fulfills functions of communication, affiliation, dominance, alliance, stress reduction and fun.

2. What evolutionary benefits does homosexuality have?

At first glance, homosexuality may seem like an evolutionary disadvantage, since it reduces the chances of passing on one's genes to the next generation. However, there are several hypotheses that explain how homosexuality can favor the survival and reproductive success of individuals and their relatives.

One such hypothesis is “inclusive kinship,” which proposes that homosexual individuals can help raise the children of their close relatives, thereby increasing the number of copies of their genes that spread through the population. This hypothesis is based on the concept of “kin selection,” which states that individuals can increase their evolutionary success not only by directly reproducing, but also by helping their relatives do so.

Another hypothesis is that of "genetic balancing", which suggests that genes that predispose to homosexuality can have positive effects on other aspects of adaptation, such as intelligence, creativity, cooperation or empathy. These traits can increase the chances of survival and reproduction of individuals who possess them, thus offsetting the cost of homosexuality. This hypothesis is based on the concept of “pleiotropy,” which indicates that the same gene can have multiple effects on different characteristics.

3. What biological and environmental factors influence homosexuality?

Homosexuality is the result of a complex interaction between genetic, hormonal, epigenetic, neuronal and environmental factors. There is no single gene or hormone that determines the sexual orientation of an individual, but rather it is a multifactorial and variable trait.

Genetic factors are those that are inherited from parents and that influence the development of the brain and the endocrine system. Some studies have identified chromosomal regions associated with homosexuality in humans and other mammals, but no specific gene responsible has been found.

Hormonal factors are those that regulate the functioning of the body and that can affect sexual development and behavior. Some hormones, such as testosterone and estrogen, have masculinizing or feminizing effects on the brain and sexual organs. Exposure to different levels of hormones during the prenatal or postnatal period can influence the sexual orientation of the individual.

Epigenetic factors are those that modify the expression of genes without altering their sequence. These changes can be induced by the environment or by the experiences lived by the individual or his or her ancestors. Some studies have suggested that certain epigenetic patterns may be related to homosexuality in humans and other mammals.

Neural factors are those that refer to the structure and functioning of the brain. Some brain regions are involved in the processing of sexual information and the generation of emotional and behavioral responses. Some anatomical and functional differences between the brains of homosexual and heterosexual individuals have been reported by various studies, but a causal relationship has not been established.

Environmental factors are those that refer to the external conditions that surround the individual and that can affect their development and behavior. These factors include temperature, resource availability, competition, social pressure, learning, and culture. Some of these factors can induce temporary or permanent changes in the sexual orientation of individuals, depending on their plasticity and sensitivity.

4. Conclusion

Homosexuality is a natural and diverse phenomenon that occurs in numerous species of mammals, including humans. Homosexuality is neither an anomaly nor a disease, but a normal variation of animal sexuality. Homosexuality has a biological basis, but it is also influenced by the environment and the history of each individual. Homosexuality may have evolutionary benefits for individuals and their relatives, as well as for the stability and diversity of populations.