A population of birds colonizes an area in which the insects upon which they fee

Question

A population of birds colonizes an area in which the insects upon which they feed live inside trees. Which of the following events accounts for an observed increase in average beak size in the bird population over time?
1) Decreased fitness of small-beaked birds, creating a new species
2) Increased fitness of the large-beaked birds, creating a new species
3) Increased fitness of large-beaked birds, leading to natural selection
4) Decreased fitness of the insects, allowing the birds to catch them more easily

Explanation / Answer

First I want to define the term "fitness." It is a measure of reprodctive success. 1) It says that the fitness of small-beaked birds decreased. So less survival. Therefore it does not follow that less survival would lead to new species. 2) Increased in fitness does not relate to speciation or creating new species. Because that is not the mechanism of evolution 3) THIS IS THE ANSWER. The large beaks are used to get insects inside the tree. So if the large birds always gets food then their offspring would survive. And this makes the large beaked birds best adaptive to their environment; the nature is selecting them and is there for natural selection. 4)This doesn't cause the average beak size of birds to be larger. Hence this is not the answer

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