That trough time, a specie of animal, plant, bacteria can change.
When a life form reproduces, one of its"babies" may be different from its parents because of genetic mutation. Sometime, this mutation may give it an advantage over other individuals of its specie. (e.g.: A giraffe has a higher neck and can search food on high trees.) Because of this advantage, the life form that is different (we will call it A) can live longer and has better chances to reproduce. The life form that has not this advantage (we will call it B) will live less longer and will have less chances to reproduce. Because of that, the population of "A" will increase and the population of "B"will decrease. In the end, there will only be "A".
Philosophy of biology is a subfield of philosophy of science, which deals with epistemological, metaphysical, and ethical issues in the biological and biomedical sciences. Basically, philosophers of biology look at scientific ideas as philosophical ones and explore their consequences.
The skin controls temperature in protecting the body's internal organs from extremes in outside temperatures and allowing them to stay within a normal, homeostatic temperature range. In outer cold weather, capillaries expand and allow for a rush of warm blood to the skin, and small hairs on the skin rise up along with the formation of goose bumps, allowing for the skin to be warmed. In warmer weather, sweating from the skin allows for the evaporation of moisture, which subsequently cools the body down.
Salt water is denser and, therefore, more buoyant than fresh water so less of your energy is expended keeping afloat, and more is used to propel you along. Phil
The technique is called MRI or Magnetic Resonance Imaging
for more info on MRI : http://en.wikipedia.org/wiki/Magnetic_resonance_imaging