In the mammals it departs from our aptitude to fight infections it is tied to a group of genes of the Biggest so called Antigen of Histocompatibilidad, whose initials in English are MHC. These constitute a complex group of different genes involved in the regulation of the immune answer and present an enormous polymorphism grade, that is to say, in the populations numerous alelos exist for every gene. For example, in the mouse it usually has of the order of 100 alelos different, therefore the highest number of possible combinations exists. The proteins codified by these genes fulfill an important role in the recognition of strange proteins on the part of a particular type of immune cells, the lymphocytes T. Therefore, the differences between the MHC of different individuals collaborate to the aptitude to recognize and to answer before different pathogenic, so that the "quantity" of present genetic changeability in the MHCs of an individual is related to his aptitude to fight infections. Simplifying very much, individuals with high changeability would possess “better genes” (in this aspect) than individuals with less changeability.
Also, the changeability of the MHC plays a role in the determination of the corporal smell of every individual, because they affect to the production of soluble proteins capable of joining volatile substances, and for it responsible for the smell. These proteins affect to the type of bacterium that can grow in the skin, what also has an indirect effect in the corporal smell as what they can be perceived by the potential couples. Therefore, it is reasonable to think that the individuals with tall variablidad in his MHCs might turn out to be more attractions as couples.
To prove this hypothesis, Hanne Lie and his collaborators of the University of Western Australia analyzed the genetic diversity in good number of volunteers (university students, as it is usually habitual), to whom also they spent a questionnaire about his sexual customs and his success in these matters. After some variables fitted (like the attitude opposite to the sex and the age of the first relation) the investigators thought that the diversity of the MHC was positively related to the sexual partners frequency. This effect was not observed by the genetic changeability in general, what he suggests that this character could have been an object of sexual selection in our species. Curiously, the effect was not also observed in the boys, without an apparent explanation existing for it.
The truth is that squedan many questions without constestar: how do the potential couples perceive the changeability of the MHC? Possibly, across the smell, but that also is necessary to demonstrate it: Does this phenomenon have an adaptive value? It is possible, but neither is an irrefutable test. In other articles it has been seen that the individuals, in many mammals species (included the human beings), tend to pair with individuals with alelos MHCs different from the proper ones; which is a different question, although also it has as a result a descent with major changeability in the above mentioned genes: are both phenomena compatible? In any case, it must be born in mind that the MHC does not constitute the only one (not vaguely the most important) “criterion of matching” in human beings.
M.I.S.N. (More Investigation will Be Necessary)
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