Evolution can be observed directly, as in the famous example of natural selectio

Question

Evolution can be observed directly, as in the famous example of natural selection and adaptation to drought in Darwin’s finch populations on Daphne Major in the Galápagos archipelago. Answer the following questions, referring to these graphs:

a) What characteristics of the graphs show that there was variation in the population? Approximately how much variation was in the population in 1976? How much variation was in the population in 1978?

b) What happened to the population size between 1976 and 1978? What other changes occurred in the population? It decreased?

c) Based on these limited data, which mode of selection seems to have operated on the finches? What evidence supports this idea? I'm guessing this is something like geographic separation?

d) Assume the drought continues for another 2 years. If natural selection is occurring, what would you expect to see in future generations? If the changes in beak size are not due to natural selection, but to genetic drift, then what would you expect to see in future generations? Thanks!

90 Before the drought 1976 All Daphne birds N=751 60 30 0 6 8 9 10 12 13 12 After the drought 1978 Survivors N=90 2 2 8 4 0 10 11 Beak depth (mm) 6 8 12 13 14

Explanation / Answer

a. In 1976, the beak depth ranges from 1mm to 12mm (some 14mm beaks too). This denotes the variation. In 1976, variance is quite high as the population of finches is distributed from 1 to 14 mm while in 1978 is has decreased to 7 to 11 mm.

b. Population size decreased. While earlier finches of very narrow and wide beak were able to survive, in 1978 the finches with beak depth 7-11 mm were able to survive.

c. Stabilising type of natural selection is happening here evidenced by the survival of the averaged beak finches.

d. Natural selection has a direction, so if it continues finches with average beak depth will be produced in the coming generation. However in genetic drift, the average beak sized finches will be produced more but there can also be other sized beak finches as genetic drift is non-directional.

Related Questions

Navigate

• Browse (All)
• Browse E
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.