Mechanisms of Evolution Questions
Bring on the tough stuff
1. In a species of beetles, males fight each other for mates, earning the right to pass on their genes. Is this natural selection or sexual selection? Why?
2. How does stabilizing selection affect the range and mean of a phenotype?
3. Briefly explain Darwin's observation of "common descent with modification" in terms of two species of ants, one with a larger body size and one with a smaller body size.
4. What could result from disruptive selection and how?
5. Why does sexual selection disrupt the Hardy-Weinberg principle?
6. Does the Hardy-Weinberg equilibrium ever really exist?
7. What are the differential effects of adaptive mutations, harmful mutations, and mutations with no protein change on natural selection?
8. Evolution is gradual. Where do we have the best chance of seeing evolution in our lifetimes?
9. Why might a harmful mutation be more detrimental in the founder effect?
10. Why might migration of two populations of the same species NOT result in gene flow between the populations? Think in terms of sexual selection and speciation.
Possible Answers
1. In a species of beetles, males fight each other for mates, earning the right to pass on their genes. Is this natural selection or sexual selection? Why?
A fight to the death causes intrasexual selection, or selection within males for their mates. Selection due to an organism's sex, and not due to environmental pressures is a type of sexual selection. Indeed.
2. How does stabilizing selection affect the range and mean of a phenotype?
This type of natural selection consistently chooses for the phenotypes that's "just right." The result is that more of the population moves towards the mean. The mean doesn't change, but there's now less variety. Now isn't that a shame? Variety is the spice of life.
3. Briefly explain Darwin's observation of "common descent with modification" in terms of two species of ants, one with a larger body size and one with a smaller body size.
Darwin would probably have taken these ants home with him and used them as a table centerpiece. Kidding. Or are we? Darwin would probably observe that these ants had a common ancestor, but that there was natural selection for two different species better adapted for their environments: one larger and one smaller.
4. What could result from disruptive selection and how?
Disruptive selection will select for the two extremes of a phenotype. Imagine that over lots of time, these two extreme phenotypes preferred different locations or mates of the same phenotype as themselves. The result could be speciation.
5. Why does sexual selection disrupt the Hardy-Weinberg principle?
The Hardy-Weinberg principle relies on random mating. If members of a species are selecting mates based on certain characteristics, the allelic frequencies of certain phenotypes are likely to change and no longer be in genetic equilibrium.
6. Does the Hardy-Weinberg equilibrium ever really exist?
Never say never. It's difficult, though. Mating is usually not random, and populations are usually not static. Natural disasters happen, and so do man-made ones. A characteristic of living things is that it is constantly adapting to its environment, or evolving. If you were to find HW equilibrium, take a picture. It might not last that long.
7. What are the differential effects of adaptive mutations, harmful mutations, and mutations with no protein change on natural selection?
Many mutations don't affect phenotype at all. Therefore, there's nothing to select for. Harmful mutations happen, but are usually selected against in a population. Adaptive mutations are the least common, but because they are selected for, they will have the most positive and observable effect on a population.
8. Evolution is gradual. Where do we have the best chance of seeing evolution in our lifetimes?
Seeing evolution of the human species is impossible, unless we compare ourselves to humans from many, many moons ago. However, we can see evolution in our lifetime just by looking at species with a shorter generation—like bacteria. So anytime you're bored, feel free to start collecting bacteria off door handles and studying it. There's plenty to choose from.
9. Why might a harmful mutation be more detrimental in the founder effect?
A founder effect involves a small group of individuals that break off from the bigger population. Because there are a small number of individuals, the gene pool is this new population is very small as well. There is not much variety. If one or more of these organisms happens to have a harmful mutation in a gene, and it survives to pass it on to multiple offspring, then it will have a higher allelic frequency in this small population then if it were diluted out in a larger population.
10. Why might migration of two populations of the same species NOT result in gene flow between the populations? Think in terms of sexual selection and speciation.
In order to be the same species, these organisms must have the ability to mate. But that doesn't mean they want to. Perhaps population A has a greater allelic frequency for cool, red, ruffled hair and population B has a greater allelic frequency for a slick purple hairstyle. Maybe most of the ladies of population A think purple hair is the worst. They'll select against it. And voilà—an anti-gene flow situation.