Based on what you know about natural selection, which of the following must be true if evolution is the explanation for what the grants have observed over time on daphne? a. food must be plentiful for all birds. b. beak depth and length must be heritable. c. beak depth and length must show variation among individuals of a single species. d. beak depth and length must affect survival and/or reproduction of birds. e. over time, individuals can evolve to better fit the environment by changing heritable traits. f. the beaks of individual birds can change depending on what food is available.

The correct answer will be options-

1.  Beak depth and length must show variation among individuals of a single species

2. Over time, individuals can evolve to better fit the environment by changing heritable traits

3. Beak depth and length must affect survival and/or reproduction of birds.

Explanation:

Charles Darwin studied the birds of the Galapagos island and concluded that organisms evolve with time by showing natural adaptation as a mechanism.

In 1973, Grants went to the Daphne major and live on the island and observed the finches for about 40 years or more visiting the place repeatedly.

His finding helped him conclude that individual can evolve by changing the traits which become heritable, the beaks showed variation in the individuals of the same species and the size of the beak affects the survival and reproductive rate of the birds.

Thus, the selected options are correct.