By activating a gene in the brains of hermaphrodite nematode worms (Caenorhabditis elegans) scientists at the University of Utah have induced them to attempt to mate with other hermaphrodites; offering interesting new evidence that homosexual or heterosexual preferences are influenced by underlying biology.
Most nematode worms are hermaphrodites, having both male and female sex organs that can fertilize their own eggs, however one in 500 nematodes is a true male. Hermaphrodites will mate with an available male in preference to fertilising themselves, because although they produce sperm they cannot impregnate other hermaphrodites, as they lack the required copulatory structure.
The ability to reproduce without a mate is important for the worms, since they might only come across food sporadically, and thus when a worm finds a bacteria bloom, it does not have to wait around to find a mate, if it is to take advantage of this nutrition, and then reproduce.
The worm’s sex is determined by chromosomes found in its DNA. If a worm is male, all the cells in the body, including those in its brain, will be male.
The scientists were unable to change the gender of the worms, but by activating a gene called fem-3 in the brains of hermaphrodite nematode worms, they were able to fool their nerve cells into acting like those of the opposite gender. So, before the genetic manipulation, the hermaphrodites showed no interest in other hermaphrodites, however, after the procedure, the genetically altered hermaphrodites moved toward them, and attempted to mate with other hermaphrodites, instead of being attracted to the males.
Nematode worms are extremely simple organisms, and details of their behaviour are difficult to apply to people with any accuracy, but the researchers claimed that the existence of a biological pathway to same-sex attraction offered a possible insight into human sexuality.
Erik Jorgensen, who led the study, said:
We cannot say what this means for human sexual orientation, but it raises the possibility that sexual preference is wired in the brain. Humans are subject to evolutionary forces just like worms. It seems possible that if sexual orientation is genetically wired in worms, it would be in people too. Humans have free will, so the picture is more complicated in people.
The study, which was published in the journal Current Biology, also found that the same nerve cells that produce male sexual behaviour are present in hermaphrodites, only they serve a different purpose. This means that both have identical brain cells resulting in different behaviours.
Posted by Jonathan in Biochemistry, Biology