Natural Selection and Evolution Flashcards

A population of beetles lives on the bark of trees that are gradually darkening over time due to industrial pollution. Within the beetle population, there is variation in color, from light gray to dark gray. Which of the following outcomes is the most likely result of natural selection in this scenario?

Answer: The frequency of the alleles for dark gray coloration will increase in the population over generations.

Natural selection acts on existing variation within a population. In this environment, darker beetles have a selective advantage because they are better camouflaged from predators on the darkening trees. As a result, they are more likely to survive and reproduce, passing the alleles for dark coloration to their offspring. Over time, this will lead to an increase in the frequency of these alleles in the population's gene pool.

The forelimbs of a human, the wing of a bat, and the flipper of a whale all contain a similar pattern of bones (humerus, radius, ulna). These structures serve different functions but suggest a shared evolutionary history. What is the correct term for these types of structures?

Answer: Homologous structures

Homologous structures are features shared by related species because they have been inherited from a common ancestor. Even though the forelimbs of humans, bats, and whales are used for different purposes (grasping, flying, swimming), their underlying skeletal similarity points to a shared mammalian ancestor.

Which of the following is required for natural selection to occur in a population?

Answer: There must be heritable variation for a trait within the population.

Natural selection can only act on traits that have a genetic basis and vary among individuals in a population. Without heritable variation, there are no differences in survival and reproduction for selection to favor, and the population cannot evolve.

In a particular species of fish, a river is dammed, separating the population into two isolated groups. The upstream environment is rocky and has fast-moving water, while the downstream environment is muddy with slow-moving water. Over thousands of years, the two groups become so genetically different that they can no longer interbreed. This process is an example of:

Answer: Speciation

Speciation is the evolutionary process by which populations evolve to become distinct species. In this scenario, the geographic barrier (the dam) leads to reproductive isolation, and the different environmental pressures in the upstream and downstream habitats drive the two populations to diverge through natural selection until they are separate species.

A strain of bacteria becomes resistant to a common antibiotic. A doctor continues to prescribe the same antibiotic to infected patients. How does this situation illustrate the process of natural selection?

Answer: The antibiotic acts as a selective pressure, favoring the survival and reproduction of resistant bacteria.

The antibiotic does not cause the resistance mutation; the variation already exists in the bacterial population. The presence of the antibiotic creates a strong selective pressure where resistant bacteria have a significant survival advantage. They survive the treatment and reproduce, passing the resistance genes to the next generation, leading to a population dominated by resistant bacteria.

The pelvic bones of modern whales are small, non-functional structures that are remnants of the hind limbs of their land-dwelling ancestors. These non-functional structures are best described as:

Answer: Vestigial structures

Vestigial structures are genetically determined features that have lost most or all of their ancestral function in a given species but were functional in an ancestor. The whale's pelvic bones are a classic example, providing evidence of their evolution from four-legged terrestrial mammals.