Chemical signal can signify the lymphatic, nervous and endocrine system.
Mostly endocrine, the endocrine system is the body system responsible for providing the needed hormones for the body. These hormones and body fluids contribute and catalyse the growth, disposition, sex characteristics and other potential corresponding output of these hormones.
An advantage to reproducing sexually, is the genetic variation the offspring will obtain.
At times, a person may have experienced a sudden or unexpected change in body temperature within a 24-hour period. This change in the body temperature is caused by immune responses. If there is a detected infection in the body, the immune system fights back thus causing the change of body temperature.
With shorter necks, giraffe ancestors could not reach food-containing branches on tall trees. This resulted in the directional selection of giraffes with longer necks.
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Why is choosing a direction necessary? </h3>
It nearly appears obvious that the giraffe's long neck developed as a result of a lack of food in the lower branches of trees. The giraffe has a significant advantage because it is taller than any other mammal and can feed where few others can.
When compared to modern giraffes, the giraffe's ancient predecessors had a shorter neck. The plants that were lying at a higher level were inaccessible to them. Giraffe phenotypes have changed in various ways, and now have long necks to reach vegetation that is higher up. The extreme form is chosen above other features in directional selection. It was decided to choose the long-necked giraffe over the short-necked.
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