week 4 hw
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Natalie Focha
25 April 2013
Anthro 7, Sec 1E
HW #3
Homework Assignment #3
5.10: Benefits to scociality include resource acquisition and defense and decreased vulnerability to predators. Costs to sociality include competition over food and mates, increased vulnerability to disease, and increased hazards from conspecifics (i.e. cannibalism, cuckoldry, incest, or infanticide). Primatologists are divided over whether between-group feeding competition or predation is the primary factor favoring sociality in primates.
6.5: When females invest more in offspring than do males, their lifetime reproductive output is limited much more than that of males. While female fitness also varies (mainly as a function of nutritional condition), it does not vary as much as in males. Consider a species living in one-male, multi-female groups. Females from groups of 10 and have on average 10 offspring each (range is 0 to 20, where 20 is the maximum reproductive success possible for females because of obligate gestation and lactation). In one-male, multi-female groups, a male who monopolizes a group for the entire reproductive careers of the females can sire 100 offspring, so the range of male reproductive success is 0 to 100. Females range from 0 to 20 offspring, and males range from 0 to 100.
When variance is high, the payoff for winning is extremely high. This creates a heavy selection pressure for individuals who compete effectively. This can result in a wide variety of characteristics in the sex with low investment/high variance in reproductive success, such as large size, weaponry for fighting, or traits that the opposite sex prefers.
7.3: The text emphasizes that the individual is the primary unit on which selection acts. There is little chance that such a behavior could evolve. Those with alleles for such behavior would not transmit them as much as others with alleles for selfishness. This behavior could not be rescued as a form of kin-selection altruism, or reciprocal altruism, because subordination benefits every individual in the group to whom the actor submits. Altruism can only evolve if it is delegated non-randomly (i.e. only toward those who also carry the altruist alleles).