Answer:
The populations become adapted to different environments and eventually become so different that they cannot interbreed to produce fertile offspring.
Speciation is the evolution of one species into two different kinds, and when they become isolated, that is the final step, since they cannot interbreed any longer.
The muscles that contract (during cold or fright), the slanted hair follicle is pulled upright, dimpling the skin surface with goosebumps are called arrector pili muscle.
The arrector pili muscle are tiny muscle that attaches to the base of the hair follicle at one end and to the dermal tissue on the other end. When the body feels cold or fright the body generate heat and the arrector pili muscle contract all at once, that causes goosebumps on the skin.
The arrector pili muscle acts as the thermoregulator. Straight stand hair increases air trapping, so that the heat loss from the body decreases. The arrector pili muscle are mediated by the sympathetic nervous system.
To learn more about sympathetic nervous system here
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<span>Fish have adaptable behaviors and structures so that they can
survive in the wild. These adaptations however differ with regards to context
and environment. Some fishes for example are called stonefish because they can
camouflage in environments that are composed variedly with pebbles and rocks,
and this helps them to avoid predators and thrive. Nevertheless, when these
group of organisms are strayed and become exposed to a new environment they can
be exposed and be vulnerable to predators. </span>
