Epigenetics is a Key Player in Sexual Preference Epi-marks act as another layer of information fused to our genes that control their expression. Essentially, genes hold the directions, while epi-marks instruct how they are put into motion and completed.
Historically, epi-marks are eliminated and created anew with each generation, but new research shows that they can occasionally pass over between generations, causing similarities within families and appearing as shared genes.
Sex-specific epi-marks are made during early fetal development and serve as security against the considerable natural variation in testosterone that happens in late fetal development. For example, sex-specific epi-marks prevent female fetuses from becoming masculine when there are unusually high testosterone levels present, and vice versa for male fetuses.
Different kinds of epi-marks safeguard different sex-specific characteristics; some protect the genitals, others protect sexual identity, and this study suggests others keep safe sexual partner preference.
When these epi-marks are passed between generations from fathers to daughters or mothers to sons, they have the potential to result in reverse effects. The outcome is feminization of characteristics in sons or masculinization of some characteristics in daughters, occasionally affecting sexual preference.
This study provides an answer to the evolutionary mystery of homosexuality, suggesting that "sexually antagonistic" epi-marks can, at times, pass from generation to generation and result in homosexuality in opposite-sex children. The mathematical modeling shows that the coding of the genes for these epi-marks can spread in the population easily because they invariably raise the fitness of the parent, but are very rarely erased and do not reduce fitness in their children.
The study's co-author Sergey Gavrilets, NIMBioS' associate director for scientific activities and a professor at the University of Tennessee-Knoxville, concluded, "Transmission of sexually antagonistic epi-marks between generations is the most plausible evolutionary mechanism of the phenomenon of human homosexuality."