Scientists say they may have discovered why homosexuality exists.
Researchers from the National Institute for Mathematical and Biological Synthesis have said the genetics that makes a person more likely to be gay are passed from fathers to daughters and mothers to sons.
They suggest the answer lies in epigenetics, or how the expression of genes is controlled by ‘temporary switches’, such as how a gene behaves, known as epi-marks.
Gender-specific epi-marks are usually ‘erased’ from generation to generation, but when they do not and they pass from a parent to a child, it can result in homosexuality.
‘Transmission of sexually antagonistic epi-marks between generations is the most plausible evolutionary mechanism of the phenomenon of human homosexuality,’ the study’s co-author Sergey Gavrilets said.
Researchers have long believed sexual orientation has stemmed from the basic makeup of a person’s DNA or their genetic line.
Some have pointed to similar brain patterns in straight women and gay men, and straight men and lesbians.
However scientists say homosexuality, in terms of evolution, cannot be solely genetic because otherwise the trait would eventually disappear given gay people are less likely to reproduce.
Epi-marks, on the other hand, are thought to have an evolutionary advantage that keeps them within the population.
For example, some epi-marks would work to protect a female fetus from becoming too masculine if testosterone spikes in late pregnancy.
The study’s lead author William Rice said these epi-marks protect fathers and mothers from excess or underexposure to testosterone, when they carry over to opposite-sex offspring, ‘it can cause the masculinization of females or the feminization of males.’
With the theory, Rice believes it could also be used to explain the occurrence of identical twins.
The researchers have not tested yet on parents, and as the epi-marks are ‘highly variable’ it can be difficult to assess. However Rice said it is the most ‘plausible explanation so far’.
‘We've found a story that looks really good,’ Rice said. ‘This can be tested and proven within six months. It's easy to test. If it's a bad idea, we can throw it away in short order.’