201-08s-13-MalesAndSexualSelection

201-08s-13-MalesAndSexualSelection - Introduction to...

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Introduction to Biological Anthropology: Notes 13 Mating: males and sexual selection Copyright Bruce Owen 2008 - Male reproductive strategy basics: - Males are not forced to invest a lot in their offspring, the way females are - males can have almost unlimited numbers of offspring - so male reproductive success can vary over a much wider range than females' reproductive success - in a typical species, females might range from zero to five offspring - in the same species, males might range from zero to fifty offspring - all females can mate as often as they need to - they virtually all reach their limit of pregnancies per lifetime - food, not access to mates, is the main limiting factor for females - but the more a male mates, the more offspring he has - in some cases, it may be to the male’s advantage to care for offspring, but this is rare - in mammals such as primates, usually selection will tend to favor traits in males that lead them to mate frequently - Sexual selection : selection that favors traits that increase male success in mating - Sexual selection is just a kind of natural selection - but it is unusual in that it often favors traits that - are mostly or only expressed in males - and that seem to be useless or even harmful to the males’ survival - the huge tails of male peacocks, for instance - that make it hard for the peacocks to escape predators - but make them more attractive to female peacocks - sexual selection favors traits like these if - if they improve the males’ reproductive success by increasing matings - more than they harm reproductive success by increasing predation or other costs - two kinds of sexual selection: - intrasexual selection: selection that occurs due to differences in success at mating that result from interactions between members of the same sex - the most common form is male-male competition - such as males fighting each other for access to females - the outcome of the interaction of the males determines which male mates; the female is not involved in the decision - example: intrasexual selection might lead to large canines becoming common among males, because the males with the largest canines can drive other males away, so they get more access to females, so they leave more offspring - intersexual selection: selection that occurs due to differences in success at mating that result from interactions between members of opposite sexes - the most common form is female choice - such as females picking the most desirable male to mate with, based on some visible trait
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Intro to Biological Anthro S 2008 / Owen: Males and sexual selection p. 2 - example: intersexual selection among peacocks might lead to large tails becoming common among males, because the female peacocks prefer to mate with males with large tails, so the large-tailed males mate more often, so they leave more offspring. -
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201-08s-13-MalesAndSexualSelection - Introduction to...

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