Suppose you were studying several species of monkeys. In one, males never helped females raise offspring. In another, males provided just as much parental care as females except for actually carrying the fetus during pregnancy. How does the fundamental asymmetry of sex compare in the two species? How would you expect sexual dimorphism to compare between the two species?

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1. Identify the fundamental asymmetry of sex in each species. This concept refers to the differences in reproductive investment between males and females. In the first species, where males do not help in raising offspring, the reproductive investment is primarily by the females. In the second species, where males provide equal parental care except for gestation, the reproductive investment is more balanced between the sexes.
2. Analyze how the differences in parental investment might influence sexual selection. In species where males invest less in offspring, typically females are more selective in mate choice, leading to stronger sexual selection pressures on males. This can result in more pronounced differences in traits that are advantageous for mating.
3. Consider the implications of these differences in sexual selection on sexual dimorphism, which refers to the differences in size, shape, or color between males and females of the same species. In the first species, expect higher sexual dimorphism due to stronger sexual selection pressures on males. In the second species, expect lower sexual dimorphism due to more equal reproductive investments and potentially less intense sexual selection.
4. Reflect on how the level of parental care provided by males might correlate with mating systems and competition. In the first species, where males do not provide care, there might be a tendency towards polygyny (one male mating with multiple females) and higher male-male competition. In the second species, with equal parental investment, monogamy (one male mating with one female) might be more common.
5. Hypothesize how these differences in mating systems and sexual dimorphism could affect the overall social structure and behavior of the species. In the first species, expect more aggressive and competitive behaviors among males, while in the second species, expect more cooperative and pair-bonding behaviors.