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SOCIAL EVOLUTION Natural Selection Natural selection- differential reproductive success of individuals Differential reproductive success- in each species some individuals leave many surviving offspring, some leave few, and some leave none at all o Pre-reproductive mortality- of the creatures conceived, most die before reaching reproductive age, and this mortality is non random, striking some individuals more frequently than others o Pre rep mortality determines differences in reproductive success o When variation in RS acts on genetic variation, there is evolution--in the sense of genetic change over time. It is critical that mortality or variation in reproduction act non-randomly , that is, favoring some at the expense of others with reference to their genetic traits. o When variability is high, selection is strong RED DEER -variation in RS Greater variation in RS for males than females Females-35% produce no surviving offspring, which some raise 13 young to age 1 males->40% produce no surviving offspring, while some father as many as 24 so, max RS of male is 2x that of female. For females, each offspring is costly to rear (proved by survival of females with vs without dependent young) Mothers in better condition give birth earlier to heavier offspring—both factors have positive effect on survival of offspring Social factors have critical influence on male RS Fall mating season, males fight with each other to control mating access to groups of females-frequency of fighting and number of injuries is positively associated with frequency with which females are conceiving Selection more intense on males than on females (aka greater variation in male RS) Female RS controlled by ability to invest in offspring while male RS controlled by ability to inseminate females Natural selection does NOT work at the group/species level---ONLY individuals Natural selection favors individuals that maximize the number of their surviving offspring Elementary social theory -social theory that applies to two individuals o B=benefit C=cost defined entirely by reproductive success which=# of surviving offspring X-----O B C=selfish C B=altruistic-ex: birds give alarm calls for danger, lioness will nurse cub of another female as long as cub of other female are smaller than her own. B1 B2=cooperative
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C1 C2=spiteful Reasons for altruism o Altruistic act is one that confers a benefit on someone at a cost to the other Cost is measured by a decrease in rep success, so altruistic acts are opposed by natural selection’s working on the actor result in production of fewer surviving offspring altruistic traits are everywhere in nature i.e. : honey bee and ant workers foregoing personal rep to help the queen reproduce, birds helping a pair raise their young, lionesses nursing cubs that aren’t their own… o natural selection favors altruism whenever Br>C, B=benefit, C=cost o Kinship - degree of relatedness: for any gene in you, the chance that it
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