2.1 billion years old 5.
Natural selection is a cause of genetic variation in a population.
With a few rare deviations, all organisms use the same genetic code. Mammals first originated about 74 million years ago, just as the dinosaurs were going extinct. Hawaiian honeycreepers are closely related to the Galapagos finches, as evidenced by the similar ecological roles that they fulfill. List three different major lines of evidence that prove the occurrence of evolution. List two reasons why RNA, and not proteins, is thought to have been the first informational system of early life forms.