Two researchers at the Savannah River Ecology Laboratory have used a computer model to look at the question of what females really look for in a mate. (Sorry, guys, this doesn't concern humans, only those species where the male is a simple sperm donor.) Christopher Beck and Larkin Powell published their findings in the journal, Evolutionary Ecology Research.
Traditional wisdom and some past research holds that females will select older males because their viability indicates better genetic material for their offspring. The SREL researchers used previous models but varied them in several fundamental ways. In the SREL model half the females were specified as "choosy," that is exhibiting a preference, while the other half were "non-choosy," or mated at random. Simulations were run in which individual females were assigned as either choosy or non-choosy and males were assigned an age. Simulations followed 1000 generations or until choosiness was either fixed or lost in the population.
What the researchers found was that in their model, female preference for older males was unlikely to become fixed in the population in most cases. Female mate choice based on male age was most likely to become fixed in the population when choosy females exhibited preferences for younger and intermediate age males. So, in species in which males contribute only sperm, female preference based on male age is more likely to evolve in a population if preferences are directed towards younger and intermediate age males. As preferences for older males were rarely selected over random mating, older males may not be better mates.
Another conclusion drawn by the researchers is that when older males are chosen, it may be on the basis of something other than just good genes. In some cases older males may simply be more available. The costs of mating are also taken into account by females. For instance, female guppies are less choosy when predators are present. However, in some species females remain choosy under various circumstances.
The conclusion is that female preference for older males may evolve as a result of good genes in some cases, but not in others or – sometimes the old guy wins, and sometimes he doesn't.
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