The oxygen diffuses out from a region of higher concentration to the region of lower concentration because of diffusion. The air contain high amount of oxygen and human body has low oxygen level so the oxygen moves from the air to the lungs of the human body from there oxygen is loaded in the hemoglobin while on the other hand, carbondioxide is removed from the blood into the lungs which goes outside the body through breathing.
Evolution is not a random process. The genetic variation on which natural selection acts may occur randomly, butnatural selection itself is not random at all.
