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Anthropology 005
Problem Set # 5
Altruism, heritability, male homosexuality, and monophyly
Fall 2018
1. Alleles that (sometimes) lower the fitness of their bearers can nevertheless spread in the population.
A. What is the difference between the way a kin-selected allele spreads and a reciprocally altruistic allele spreads?
Kin selection refers to the altruistic behavior of individuals and groups only to their peers. It can give psychological safety to the same kind.Reciprocal altruism means that the proceeds from the beneficiary will outweigh the cost of the donor.
B. Based on what you learned in Chapter 11, is Xq28 a kin-selected altruistic allele? Explain why or why not.
Yes. Although Xq28 is a homosexual genetic gene, it is also a kin-selected altruistic allele because its inheritance preserves the integrity and diversity of human genes.
2. Remember that heritability (h2) = Vg / (Vg + Ve).
A. In words, what is heritability?
Heritability mainly refers to the hereditary nature and the proportion of variation observed in specific traits, which can be attributed to the comparative relationship between hereditary factors and environmental factors.
B. Environmentality (e2) is the mathematical complement of heritability, that is:
e2 = 1-h2 = [Ve / (Vg + Ve)]. So, in words, what is environmentality?
Environment is the influence of natural environment on the heredity of organisms. It mainly explains the magnitude of the variation of a character affected by the environment.
C. Let’s think about a “pair-bonding” l ocus (pair-bonding is the tendency for a female and male to stay together after they copulate). Assume that this locus currently has two alleles, j and k, and that this is the only locus that carries alleles that affect pair bonding (almost certainly an oversimplification, but this is a thought experiment to help you understand heritability). Assume codominance at this locus and that, on average, the j allele is associated with stronger pair bonding. In this example is pair-bonding heritable? Explain.
Yes, this is an example of pair-bonding heritable. Because they have different alleles (J and K), they have different preferences. This example is inheritable because there are variations in genes.
D. In a population where pair bonding is favored by selection the frequency of the k allele will eventually be zero. What will the genetic variance (Vg) of pair bonding be at that point? Explain.
Zero. VG is the phenotypic variation of different genes affecting traits. So the K=0 at that time meant that this shape would not be inherited.
E. What will the heritability (h2) of pair-bonding be at that point? Explain.
In equilibrium, the heritability of pairwise binding is zero. Allele J is the first choice. Allele K will gradually disappear as time goes by, so the paired phenotypic variation is only half of the heritability.
F. At that point would it be correct to say that people do not inherit their pair-bonding tendencies? Explain.
No, because the pairing of genes still exists and is being transmitted. This is because the lack of inheritance is not the same as inheritance.
G. Why do we have to assess the heritability of male homosexuality before considering whether this trait needs an evolutionary explanation?
Male homosexuality cannot produce offspring, so their genes cannot be inherited like other normal genes, so we must assess the heritability of homosexuals before considering whether this trait requires evolutionary explanation.
3. Most evolutionists use cladistic methods of constructing natural groups.
A. What does the pattern of lines on a cladogram (see next page) supposedly represent?
From the pattern of lines we can see the process and way of evolution, and we can also see the classification of each organism and the relationship between them. And the whole process of genetic evolution can be seen that common ancestors can also be obtained.
B. Explain how a cladogram is like the diagrams used to depict family genealogies.
Branch maps are very similar to human genealogy. We can find the relationship between each part by this branch map and find out how they relate to each other, as well as the sequence of development and evolution. Just like in a family, from ancestors to the youngest generation can be queried.
C. Cladistics relies on the principle of monophyly. What are the features of a monophyletic group?
The characteristics of monophyletic groups are that there is only one common ancestor and all descendants come from the same ancestor, which is clearly distinguished from other groups.
D. In the top cladogam on the next page, is Pongidae a monophyletic group? Why?
No. Because in a monophyletic group, all the dead from the same ancestor belong to this group.
E. In the bottom diagram is Pongidae a monophyletic group? Why?
Yes. Because they have a common ancestor and are branched correctly.
F. Which (if either) diagram is cladistically more defensible? Why?
The bottom diagram. In my opinion, branch graphs are separated based on standard features or common ancestors, and obviously, the bottom diagram fits this feature better.
