During his work, Darwin observed that the size and shape of finches' beaks varied between islands as a consequence of the food type and food availability in each island. Darwin proposed that this phenotypic variation was a response to natural selection, i.e., those organisms with more suitable beaks in their corresponding environments (i.e., islands) would be better adapted to survive and reproduce, thereby passing their genes to the next generations. In consequence, in this case, it is expected that the average size of finch beaks will be smaller because environmental factors prevent the growth of large seeds.
It is called Fluid Mosaic Model. It describes the structure of the plasma membrane as a mosaic component. The structures such as phospholipids, protein, carbohydrates and cholesterol gives the fluid like character of the plasma membrane.
