The class Mammalia includes about 5000 species placed in 26 orders. Systematics do not agree on the exact number or on how some orders and families are related to others.
The animal diversity generally follows the arrangement used by Wilson and reader. The dependence of the young mammal on its mother for nourishment has made possible a period of training. Such training permits the non-genetic transfer of information between generations. The ability of young mammals to learn from the experience of their elders has allowed a behavioral plasticity unknown in any other group of organisms and has been a primary reason for the evolutionary success of mammals.
Last date updated on February, 2021