A population of 15 birds inhabits a fairly new island. Ten of the birds are dark brown, and five of them are light brown. By chance, two of the dark brown birds and three of the light brown birds die before producing any offspring. All of the birds in the next generation are dark brown. This change in phenotypic frequency can be attributed to __________.

• A. natural selection
• B. gene flow
• C. sexual selection
• D. mutation
• E. genetic drift

Answer: (E)

Verified step by step guidance

1. Identify the initial population composition: 10 dark brown birds and 5 light brown birds, totaling 15 birds.
2. Note the random deaths: 2 dark brown birds and 3 light brown birds die before reproducing, leaving 8 dark brown birds and 2 light brown birds.
3. Observe the next generation: all birds are dark brown, indicating a change in phenotypic frequency.
4. Understand the concept of genetic drift: it refers to random changes in allele frequencies in a population, often having a more significant effect in small populations.
5. Conclude that the change in phenotypic frequency is due to genetic drift, as the random deaths led to a shift in the population's genetic makeup without any selective pressure.