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publicado em 15/06/2013 às 11h26:00
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A novel explanation for the origin of menopause: accounting for the Men

The new study might change the way some scientists describe how our species evolved, published June 14 in PLOS

 
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Ilustração: M. Belan/MacMaster University
Ilustração: M. Belan/MacMaster University
Parte do ilustração que mostra a evolução da mulheres com base em sua condição reprodutiva Grafico da MacMaster University mostra a evolução feminina de acordo com as condições de fertilidade.
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Parte do ilustração que mostra a evolução da mulheres com base em sua condição reprodutiva
Grafico da MacMaster University mostra a evolução feminina de acordo com as condições de fertilidade.

Three faculty members in the Department of Biology have published a novel explanation for the origin of menopause, which might change the way some scientists describe how our species evolved! Their work was published June 14 in PLOS Computational Biology.

Professor Rama Singh has been interested in human evolution for a long time and had formulated an idea about how mating behaviour might have affected fertility. To test his idea, he enlisted fellow ' coffee-mafia' colleagues Dick Morton (Professor Emeritus) and Jon Stone (SHARCNet Chair in Computational Biology) to develop a computational model.

The team used computer simulations to evolve virtual (human) populations. Populations initially comprised individuals who lived long lives, reproducing throughout. When a mating preference for younger females was introduced in males, natural selection became relaxed in older females. Natural selection, the process described by Darwin and Wallace, operates to eliminate from populations traits (and the gene alleles that encode them) that have a negative impact on individual longevity and fertility (measures of ' fitness' ). Female-specific mutations that diminished fertility late in life became effectively neutral and accumulated over time in females. Because older males continued to reproduce, natural selection continued to operate negatively on corresponding male-specific late-onset mutations, which, therefore, never became effectively neutral nor accumulated in males. Consequently, only female fertility declined with age. The authors emphasise in the paper that the roles of the sexes reverses if the mating matrix used encodes female preference for younger males and, also, that the mate-preference change that was introduced in the computer simulations may be viewed equivalently as younger females out-competing older females for access to males.

Menopause may be defined as ' a high proportion of expected time in adulthood during which an individual is non-reproductive.' This definition reveals that menopause is rare among species in the animal kingdom, observed in humans (and possibly also in some whales). The researchers' new explanation for this essentially human trait is remarkable in being non-adaptive. The most-popular explanation hitherto, ' the grandmother hypothesis,' is used to assert that menopause originated because, then, older females could increase their genetic contribution to future generations by helping to rear their grandchildren; that such a change must have been adaptive is obvious, because a grandmother typically shares half as many genes with her grandchildren as with her own children. Helping daughters in rearing grandchildren presumably more than accounted for the ' twofold cost' of menopause, but the data that have been collected to test this hypothesis are inconclusive. The new, neutral hypothesis requires no ' adaptationist' presumption. Of course, the neutral hypothesis, the grandmother hypothesis, and any among the myriad other hypotheses may be combined to explain the origin of menopause; but the neutral hypothesis is the most parsimonious and sufficient.

From a practical perspective, real candidates for the mutations in the computer simulation might be sought for in human genomes. If any genes were found, then researchers could test whether those genes impart effects on other aspects of human life history, advancing research in human health.

Team members also are members in the Origins Institute at McMaster University, for whi

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origin of menopause    menopause    how our species evolved    accounting for the Men    McMaster University    Rama Singh   
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