Kiera Goff
Biology 303
Dr Ely
8 November 2008k
Are Human Mating Patterns Based on Our Genes?
Although it is generally accepted that human mating is based on personal choices, new studies have found that the mating patterns of males can be predicted based on their genes. Many behavioral preferences are based on the chemical makeup of the brain and the regulation of hormones. These variations are largely due to differences in an individual’s genetic makeup. Specifically males have been found to have genes that can influence his likeliness for him to be gay and/or monogamous. Although there is a wide array of possible environmental causes, it seems that there are also some biological and genetic origins in the way that humans and other animals choose and interact with their mate.
Since the mid-1990’s, many behavioral geneticists have been intrigued by the possibility of a “gay gene”. Although it is still very speculative, it has been suggested that there are genetic factors transmitted on the X chromosome which increase the probability of male homosexuality. In 2004 Camperio-Ciani et al. (1) published an article in Proceedings: Biological Sciences detailing their findings in regards to the origins of male homosexuality and the possible reasons it survived natural selection. Camperio-Ciani et al. studied the sexual orientation of the lineage of 100 heterosexual men and 98 homosexual men from northern Italy. Through a regression, they found that 14% of the variances in sexual orientation were due to relatives in the maternal line. This finding helps to promote the idea that homosexuality is at least in part controlled by an X-linked gene. Another study found that the chromosomal region Xq28 contributes to homosexual orientation in males(3). The Xq28 is the subtelomeric region of the long arm of the X chromosome. In Dean Hamer’s study (3), the linkage markers on the Xq28 region had a peak lod score of 4.0, which gave the researchers a statistical confidence level of more than 99% that this region of the chromosome contributes to male homosexuality. This finding is important because it identifies a specific region of the genome which can be further studied.
Since homosexual men often have no biological children it seems unlikely that a gene to control male sexuality would last very long; however, it has been found that having this gene can also be beneficial for survival. It seems that the relatives of homosexualsare more fertile (1). Through the study of family pedigrees, they found that the females in maternal lines of homosexuals were more fertile than the relatives of heterosexuals. They also found that there were no significant differences in the paternal relatives of homosexuals. If the relatives of homosexuals are more fertile it could possibly offset the lack of progeny from male couples, and keep the gene in the population. To date, no significant connection has been found between a gene and the sexual orientation of females.
All animal mating patterns entail much more than the sex of the partner, there is a complex network of social relationships. Monogamy is often accepted as the pair-bonding patternfor humans. Many cultures across the world practice different patterns including polygamy, and serial monogamy. Serial monogamy is the habit of having numerous long-term romantic relationships in a row. This pattern of changing partners has been frequently linked to a specific gene. Men with the AVPR1A gene have been found to be more likely to have problems in their monogamous relationships (4). Walum et al (4) studied the way that almost 2,000 couples viewed their relationships based on a Pair Bonding Scale (PBS). The PBS tested the way that the partners felt about:partner specific affiliative interactions, spatial closeness between partners, the types of time spent together, and attitudes towards the stability of the relationship. The study also looked at the genome of the participants. In particular, a gene has been identified that appears to control social bonding behaviors in voles and other rodents. The results were that only 15% of men not carrying the 334 allele, reported marital crisis; whereas 34% of the men carrying two copies of the allele reported marital crisis. That makes men carrying the allele nearly twice as likely to have problems with monogamy as those without the gene. They also found that the men’s partners scored the men carrying the 334 allele lower on the PBS than those with no allele; however, there was not a significant difference between men carrying one or two copies of the gene. Overall the results of this study were conclusive in finding that the 334 allele influences the ability of men to remain in a monogamous relationship. Although these findings are very interesting, another study done by Fink, et al. (2) found that in voles, the AVPR1A gene is not by itself responsible for monogamy.
No human behavior is completely due to genes. Behavior is also developed through environmental factorsand other elements influencing any behavior. Because of this, it is difficult to predict the relationship between social dynamics and genes. This is especially hard in humans because of ethical limitations to human experiments. The study of the genetic basis of human-human interactions is a budding science, but could lead to very interesting findings. As new relationships are found and tested it is important to remember that no action is dictated by genes. A boy with a “gay gene” might grow up to be either homosexual or heterosexual, and a man with a “cheating gene” could have a very happy and successful relationship, or could experience marital discourse. Any behavioral gene is a factor and not the bottom line.
BIBLIOGRAPHY
1. Camperio-Ciani, Andrea; et al. (2004) Evidence for Maternally Inherited Factors Favoring Male Homosexuality and Promoting Female Fecundity. Proceedings: Biological Sciences, 271(1554), 2217-2221.
2. Fink, Sabine; et al. (2006) Mammalian Monogamy is Not Controlled by a Single Gene. PNAS, 103(29), 10956-10960.
3. Hamer, Dean H.; et al. (1993) A Linkage Between DNA Markers on the X Chromosome and Male Sexual Orientation. Science, 261(5119), 321-327.
4. Walum, Hasse; et al. (2008) Genetic Variation in the Vasopressin Receptor 1a Gene (AVPRIA) Associates with Pair-Bonding Behavior in Humans. PNAS, 105(37), 14153-14156.