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Genes may help predict infidelity, study reports
Nov. 30, 2006
Special to World Science
The chance that infidelity will intrude on a romantic relationship may be partly written in the couple’s genes,
a study has found. The results suggest a DNA test could
tell a man the rough chances his female partner will cheat on him, though
it wouldn’t necessarily work the opposite way. The Infidelity discovered by Augustus Leopold Egg, 1858.
A wife collapses after her husband finds a letter revealing
betrayal. (Tate Gallery, London)
The study found that women act less passionately toward—and are likelier
to
cuckold—partners who share genes with them in a special part of the genome. This may in part
reflect an evolutionary mechanism to reduce inbreeding, the investigators speculated.
Infidelity touches about half of all couples, married
or not, according to Not Just Friends,
a 2002 book by psychiatrist and infidelity researcher Shirley Glass.
And last year, scientists reported that one
in 25 dads may be unknowingly raising another man’s child.
In the new study, researchers with the University of New Mexico, Albuquerque, focused on a set of genes
that past studies have implicated in a link between sexual attraction and genetic similarity.
The cluster of genes is termed the major histocompatibility complex, or MHC.
The genes, on human Chromosome 6, are involved in immune responses. The study is the first “to test the hypothesis that MHC similarity predicts aspects of actual human sexual relationships,” the researchers wrote. The findings appeared in the October issue of the research journal
Psychological Science.
MHC genes produce molecules that enable cells to recognize intrusive parasites.
The molecules and the genes are extremely diverse and fast-evolving. Biologists think
these traits may be evolutionary mechanisms to help organisms stay a step ahead in the arms race with parasites.
This may also explain past studies suggesting that humans and animals prefer mates with dissimilar MHC genes, according to some scientists. Such a preference might help assure that offspring have a wide range of immunity genes in the holster, giving them an edge over
pathogens.
Studies have even pointed to a possible route by which people subconsciously
assess potential mates’ MHC compatibility: smell. In the mid-1990s, researchers found that people
sniffing T-shirts worn by others tended to prefer the odor of those whose wearers were
least like them in this genetic region.
Several years later, scientists linked similar preferences
to sexual fidelity in birds. Illegitimate chicks in three species of typically monogamous shorebirds showed up mostly in the nests of gentically similar parents, investigators
found—although it wasn’t clear whether the major histocompatibility
genes specifically played a role. The study appeared in the Oct. 10, 2002 issue of the research journal
Nature.
The new study echoes elements of both previous studies.
The researchers studied 48 male-female couples who were either dating “exclusively,” by their description, or married or living together.
As the proportion of MHC genes the couple shared increased, “women’s sexual responsivity to their partners decreased, their number of [outside] sexual partners increased, and their attraction to men other than their primary partners increased,” the researchers wrote in a paper describing their findings.
Two quantities were almost equal on average, according to Christine Garver-Apgar, the study’s lead
author: the fraction of MHC genes shared, and the woman’s number of
extra partners. In other words, if the man and woman had half
the genes in
common, the woman would have on average nearly half a lover
on the side.
But these tendencies were found only for women; men’s attraction and likelihood of cheating appeared unrelated to
the genes, the researchers wrote.
Nor did these molecular statistics seem to affect other aspects of relationships. “MHC
sharing,” the scientists wrote, “does not broadly predict relationship
satisfaction.”
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The chance that infidelity will intrude on a romantic relationship may be partly written in the couple’s genes, researchers have found in a new study. The results suggest DNA tests might reveal the approximate likelihood that a man’s female partner will cheat on him, though not necessarily the other way around. The study found that women are less fond of men whose genes are similar to their own in a specific region of the genome. And if romantically involved with such men, women seem more prone to cheat on them than on other partners. The tendency may in part be an evolutionary mechanism to forestall inbreeding, the investigators speculated. The research focused on a set of genes implicated through past studies in a link between sexual attraction and genetic similarity. The genes are termed the major histocompatibility complex, or MHC, a cluster of genes on human Chromosome 6. These produce molecules that aid in immune responses. It was the first “to test the hypothesis that MHC similarity predicts aspects of actual human sexual relationships,” the researchers wrote. The findings appeared in the October issue of the research journal Psychological Science. The genes they studied molecules that enable cells to recognize intrusive parasites. These molecules and genes are noted for being highly diverse. Biologists think this diversity may be an evolutionary mechanism to help organisms stay a step ahead in the arms race with parasites. This may also explain past studies suggesting that humans and animals prefer mates with dissimilar MHC genes, according to some scientists. Such a preference might help assure that offspring have a wide range of immunity genes in the holster, giving them an edge over pathogens. People’s odor, studies have found, may help them subconsciously judge other people’s genetic compatibility with them with respect to these genes. In the mid-1990s, researchers found that people smelling T-shirts worn by others tended to prefer the odor of those whose wearers were most unlike them in the major histocompatibility genes. Several years later, scientists found evidence that similar preferences influence sexual fidelity in birds. “Illegitimate” chicks in three species of typically monogamous shorebirds showed up mostly in the nests of gentically similar parents, the investigators found, although it wasn’t clear whether the major histocompatibility genes played a role in this case. The study appeared in the Oct. 10, 2002 issue of the research journal Nature. The new study echoes elements of both previous studies. The researchers with the University of New Mexico, Albuquerque, studied 48 male-female couples who were either dating “exclusively,” by their description, or married or living together. As the proportion of the genes the couple shared increased, “women’s sexual responsivity to their partners decreased, their number of [outside] sexual partners increased, and their attraction to men other than their primary partners increased,” the researchers wrote in a paper describing their findings. They did not specify, though, how many additional partners were associated with a given increase in genes shared. Attempts to reach members of the research group for comment were unsuccessful. The researchers did write that the findings were all statistically significant—with less than 5% probability that such results would occur by chance—and the results were even stronger when women were ovulating. However, these tendences were found only for women: men’s likelihood of cheating appeared to be unrelated to the similarity of the genes.