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Ch. 23 - Evolutionary Processes
Freeman - Biological Science 7th Edition
Freeman7th EditionBiological ScienceISBN: 9783584863285Not the one you use?Change textbook
All textbooksFreeman 7th EditionCh. 23 - Evolutionary ProcessesProblem 10
Chapter 23, Problem 10

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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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.
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.
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.
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.
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.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Fundamental Asymmetry of Sex

The fundamental asymmetry of sex refers to the differences in reproductive investment between males and females. Typically, females invest more energy in producing and nurturing offspring, while males often compete for access to females. This asymmetry influences mating behaviors, parental roles, and evolutionary strategies within species.
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Parental Care

Parental care encompasses the behaviors exhibited by parents to ensure the survival and well-being of their offspring. In the context of the two monkey species, the level of male involvement in parenting can significantly affect offspring development and survival rates, reflecting the evolutionary pressures and social structures of each species.
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Sexual Dimorphism

Sexual dimorphism refers to the differences in size, shape, or color between males and females of the same species. These differences often arise from evolutionary pressures related to mating strategies and parental roles. In the context of the two monkey species, one might expect greater sexual dimorphism in the species where males do not participate in parental care, as competition for mates may drive more pronounced physical differences.
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Related Practice
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Determine what is incorrect in the following statement: Deer mice living on beaches mutated their genes so that they could have white fur color, providing better camouflage to survive on beaches.

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Draw a small concept map showing how selection, genetic drift, gene flow, and mutation relate to genetic variation.

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In humans, albinism is caused by loss-of-function mutations in genes involved in the synthesis of melanin, the dark pigment in skin. Only people homozygous for a loss-of-function allele (genotype aa) have the albino phenotype. In Americans of northern European ancestry, albino individuals are present at a frequency of about 1 in 10,000 (or 0.0001). Assuming that genotypes are in Hardy–Weinberg equilibrium, what is the predicted frequency of Caucasians in the United States who carry a single allele for albinism?
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Textbook Question

Human activities are causing the fragmentation of the Brazilian Atlantic rain forest. One result is that toucans have become extinct or nearly extinct in some of the forest fragments. Does the absence of toucans affect the forest?

Toucans disperse seeds of key forest species such as juçara palms by eating the fruit and defecating the seeds in new locations, sometimes more than a kilometer away. If there are no toucans, is the genetic diversity of palms likely to increase or decrease within forest fragments? Why?

a. Increase (due to increased genetic drift)

b. Decrease (due to decreased gene flow)

c. Decrease (due to decreased mutation rate)

d. Decrease (due to decreased natural selection)

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Textbook Question

Human activities are causing the fragmentation of the Brazilian Atlantic rain forest. One result is that toucans have become extinct or nearly extinct in some of the forest fragments. Does the absence of toucans affect the forest? Toucans can eat fruits with large seeds because their large bills can open wide. Most other birds in the same forest can only eat small seeds. Ecologist Mauro Galetti and his colleagues measured the seed sizes of palms in forest fragments with and without toucans. The graphs show two of the forest populations they studied. What is the take-home message of the data?

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