EVOLUTION
NATURAL SELECTION
Natural selection, resulting from the environmental conditions in which an organism lives, can have one of three different influences on a population. It can be stabilizing, directional or diversifying. The stabilizing influence can be seen where conditions have remained unchanged over a long period of time. The resultant environment consequently supports a well-balanced population of animals and plants in which evolutionary development is disadvantageous. Under such circumstances any change occurring in a plant or animal will bring it out of the environment's neat, efficient, time-honoured survival pattern and put the creature at a disadvantage, eventually resulting in its extinction. Its more conservative contemporaries on the other hand will survive. Animals that have been subjected to stabilizing selection for a long period of time may seem quite unspecialized and primitive compared with those of similar ancestry that have experienced a more eventful evolutionary history. Often they are characterized by passive survival mechanisms such as heavy armour, or high fecundity to offset losses through predation.