Natural selection is an evolutionary mechanism that is caused by what

when one allele makes an organism more or less fit, that is, able to survive and reproduce in a given environment.

The answer is Advantageous traits become more common in a population.

I had this on a test.

Have a great day.

answer: accepted answer: aquatic animals use the oxygen dissolved in water to carry out respiration. since the amount of dissolved oxygen in water is low as compared to the amount of oxygen in the air, therefore the rate of breathing in aquatic animals is much faster than it is in terrestrial animals.

explanation:

answer: b

coz red blood cells marrow and circulates the body for 120 days.