Darwin's Theory (Practice Quiz)

Natural selection is affected by ____________________ (variations, competitions), or traits that are different in members of the same species.

variations

Explain how environmental change can lead to adaptation.

A significant change in the environment might mean that new traits are now most beneficial. Now, it will be individuals with those traits that are selected. They will pass the traits on to their offspring, and the species will adapt to the new environment.

How did looking at fossils help Darwin form his theory of natural selection?

Darwin noticed that some of the fossils that he saw resembled organisms that were alive in his day such as the fossils of giant sloths that looked a lot like the sloths that he had seen. He began to wonder about how organisms change over long periods of time.

How did studying selective breeding help Darwin develop his theory of evolution?

Darwin observed that animals with a desired characteristic could be produced by allowing only those individuals with the characteristic to mate. He thought that a process similar to selective breeding might occur in nature.

Darwin observed differences between organisms on the Galapagos Islands and the mainland. What did Darwin think caused these differences?

Darwin proposed that a small number of organisms managed to reach the islands from the mainland. Once on the island, the offspring of these organisms gradually adapted to island conditions.

A horse and a donkey can mate with each other. Their offspring, called a mule, is not fertile. Do horses and donkeys belong to the same species? Explain your answer.

No, horses and donkeys do not belong to the same species. Two organisms belong to the same species only if they can mate and produce fertile offspring.

Suppose a small group of animals from Alaska were dropped on a tropical island. Explain the changes in the selective pressures that might be taking place.

The animals from Alaska are adapted to a cold environment. Selections probably favors animals that are good at keeping themselves warm. On the tropical island, those animals might now be too hot. Now, selection will favor those individuals that are able to cool themselves off well. Maybe the organisms will evolve less fat or fur.

A scientist collects wild rabbits that live at sea level and moves them to the mountains. One year later, the scientist discovers that the same rabbits have larger lungs, which help them breathe the thin mountain air. The scientist returns the rabbits to sea level. Will the offspring of the rabbits have larger-than-normal lungs? Explain.

The offspring probably will not have larger lungs. Their environment, not their genes, produced the larger lungs of the rabbits kept in the mountains. Only traits that are controlled by genes can be acted upon by natural selection and passed on to offspring. (If the larger-lung trait were controlled by genes, the rabbits would have shown the trait before being moved to the mountains.)

Explain how overproduction and variation work in the context of natural selection.

When more offspring than can survive are produced, it is called overproduction. Variation among these offspring exists. The offspring with variations more suited to their environments will be more likely to survive. The traits of those individuals will then be passed on to their offspring.

The only traits that can be acted upon by natural selection are those that are controlled by ____________________ (the environment, genes).

genes