Researcher: Over the course of three decades, we kept records of the average beak size of two populations of the same species of bird, one wild population, the other captive. ██████ ████ ███████ ███ ███████ ████ ████ ██ ███ ███████ █████ ███ ███ ███████ █████ ███ ███████ ████ ████ ██ ███ ████ █████ █████████ ██████████████
Why did the average beak size of wild birds shrink while the average beak size of captive birds stayed constant?
Any hypothesis explaining these findings must state a difference between the birds in the wild and the birds in captivity that explains why the beaks of the wild birds apparently shrunk. It may be a physical difference between the bird populations or it may be a difference in the way the birds were apprehended and measured.
Which one of the following, ██ █████ ████ █████ ██ ███████ ███ ████████████ █████████
The small-beaked wild █████ ████ ██████ ██ ███████ ███ ███████ ████ ███ ████████████ ████ ██████
This does not explain why the average beak size of wild birds decreased. It would explain why wild birds had smaller beaks than captive birds, but does not state that they became any less difficult to capture over time.
The large-beaked wild █████ ████ ██████ ██ ███████ ███ ███████ ████ ███ ████████████ ████ ██████
This does not explain why the average beak size of wild birds decreased. Even if more large-beaked wild birds were captured, it remains a mystery why their average beak size decreased over time.
Changes in the ████ ██████ ████ ██████ ██████ ███ █████ ██████ ███████ ███ ████████ ██ ████████████ █████ ████ ████████████ ██████
This explains why wild birds’ beaks shrunk over the study period. Birds with smaller beaks were favored by natural selection, so they became more prominent in the wild, while captive birds did not experience that change.
The average body ████ ██ ███ ███████ █████ ████████ ███ ████ ████ ███ █████ ███████
This consistency among captive birds does not explain why the wild birds’ beaks decreased in size. It is possible the average body size of wild birds remained the same as well.
The researcher measured ███ █████ ██ ████ ██ ███ ████ █████ ██ ████ ████ ███ █████████
This does not explain why the wild birds’ beak measurements decreased. It is not implied that the birds measured repeatedly had beaks that were any larger or smaller than average.
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