Which statement best explains why natural selection requires genetic variation?

Which of the following describes the most likely order of events in allopatric speciation?

The Dunkers are a religious group that moved from Germany to Pennsylvania in the mid-1700s. They do not marry with members outside their own immediate community. Today, the Dunkers are genetically unique and differ in gene frequencies, at many loci, from all other populations including those in their original homeland. Which of the following likely explains the genetic uniqueness of this population?

Many songbirds breed in North America in the spring and summer and then

migrate to Central and South America in autumn. They spend the winter in these

warmer areas, where they feed and prepare for the spring migration north and

another breeding season. 

Two hypothetical species of sparrow, A and B,

overwinter together in mixed flocks in Costa Rica. In spring, species A goes to

the east coast of North America, and species B goes to the west coast. What can

you say about the isolating mechanisms of these two species?

The peppered moth provides a well-known example of natural selection:

• The light-colored form of the moth was predominant in England before the Industrial Revolution. 
• In the mid-nineteenth century, a dark-colored form appeared. 
• The difference is produced by a dominant allele of one gene. 

Should the two forms of moths be considered separate species?

Given a population that contains genetic variation, what is the correct sequence of the following events under the influence of natural selection?

1. Well-adapted individuals leave more offspring than do poorly adapted individuals.

2. A change occurs in the environment.

3. Genetic frequencies within the population change.

4. Poorly adapted individuals have decreased survivorship.

A biologist doing a long-term study on a wild spider population observes increased variation in silk thickness. Which of the following could the spider population be experiencing?

You sample a population of butterflies and find that 56% are heterozygous at a particular locus. What should be the frequency of the recessive allele in this population?

Of the following anatomical structures, which is homologous to the bones in the wing of a bird?

Parasitic species tend to have simple morphologies. Which of the following statements best explains this observation?