One way to study evolution is by looking at remains of the past life, or fossils. You could also determine relationship by looking at patterns of development or . Other ways to study evolution is by comparing sequences of their and looking at their structures. If species were once related by a in the past, but became more and more different like the arm bones of mammals, they show evolution. The bones would be structures. If species were not related but somehow have similar structures because of similar selection pressure, they show evolution. Sharks, dolphins, and penguins for example have fins as structures. Sometimes organisms may have a structure, an organ or structure that has no useful purpose anymore and can give evidence of the past ancestor. An example of this is a .

To answer this question, researchers studied populations of the dusky salamander (desmognathus ochrophaeus) living on different mountain ranges in the southern appalachian mountains. the researchers tested the reproductive isolation of pairs of salamander populations by leaving one male and one female together and later checking the females for the presence of sperm. four mating combinations were tested for each pair of populations (a and b)—two within the same population (female a with male a and female b with male b) and two between populations (female a with male b and female b with male a). the proportion of successful matings for each mating combination was measured. for example, when all the matings of a particular combination were successful, the researchers gave it a value of 1; when none of the matings were successful, they gave it a value of 0. then the researchers calculated an index of reproductive isolation that ranged from 0 (no isolation) to 2 (full isolation). the reproductive isolation value for two populations is the sum of the proportion of successful matings of each type within populations (aa + bb) minus the sum of the proportion of successful matings of each type between populations (ab + ba). the table provides data for the geographic distances and reproductive isolation values for 27 pairs of dusky salamander populations.

Body temperature is tightly regulated in mammals for example when external temperatures drop too much the body of a mammal responds by in order to its core temperature?

Which term describes a normal value for something in the body? a.homeostasis b.set point c.feedback loop d.integration center