14 DAY TRIAL // They say that for love a chemical attraction between the two is necessary.
Chemistry indeed seems to be a requirement in a relationship, or at least for a male to be sure that he grows his own biological children.
A recent research pointed out that a group of genes linked to the immune system could forecast how sexually attracted a woman is by her partner and her degree of faithfulness: the higher the dissimilarity inside the major histocompatibility complex (MHC) genes, the higher the sexual compatibility. "There's this idea of romantic chemistry, but until now we haven't been able to pinpoint anything that predicts it," said lead researcher Christine Garver-Apgar, a psychologist at the University of New Mexico.
"These are some of the first findings that I know of that get at this idea of romantic chemistry and what it is exactly that makes two people just so compatible and attracted to each other," said Garver-Apgar.
The MHC genes encode protein receptors that cover the cells' membrane and warn the immune system about the nature of a cell: a native or an invading germ. Higher MHC variation means the immune system can detect more foreign cells and the offspring's fitness is increased.
The team investigated 48 couples, aged 18 to 35. The females were surveyed while in the fertile period of their menstrual cycle and during their infertile period.
The researchers assessed a person's overall satisfaction using questionnaires about the current romantic relationship, sexual contentment, number of sex partners and sexual attitude. Levels of luteinizing hormone, which tunes ovulation, were employed to assess the period of menstrual cycle.
The results showed that opposites did attract, especially during ovulation, at the peak of a woman's fertility. "As the [MHC] similarity increases, women are more turned off toward the guy sexually and more likely to be fantasizing about other men, specifically when she's at the fertile point in her cycle," said study team member Randy Thornhill, a biologist at the University of New Mexico.
Women in similar-MHC relationships actually cheated more their men during this period. "This speaks to the possibility that women do seek sex outside of the relationship for a particular reason and it's to possibly obtain genetic benefits, whether those are good genes or compatible genes," said Garver-Apgar.
Men did not display variations in their libido toward their partners; they do not invest much into reproduction and just look for copulation whenever the opportunity emerges.
Previous researches have revealed that some mice, birds, fish and lizards can smell a potential mate's MHC type and the same mechanism is suggested for humans, with scent molecules released through a person's glands on their skin.