Why do Women Have Only Two Breasts
February 7th 2010 -
Viewed large, sometimes small but always two – the female breasts, it is only in pairs, that seems completely natural. But when we look into the animal kingdom is striking: The number of milk glands, there is an enormous range. It ranges from two to 24 in the rodent family with the distinctive name Mastomys. But why humans have evolved precisely two milk glands, and not four or three? What determines the number of mammary glands in humans and animals?
“The human being is judged objectively, is a mammal,” says Sabine Wenisch. “The number of teats in mammals is adapted to the average litter size.” As a rough rule of thumb: The teat number represents the average number of pups times two. This example also applies to the much tit mouse, it has supplied with its 24 teats usually 12 juveniles. Animals such as horses or goats, to get the average, only one cub, accordingly have only two stations at the milk bar. “In principle, this same man also is divided in,” says Wenisch. Only about 1.2 percent of cases occur in humans of a twin birth.
However, there are exceptions to this rule, such as in the cow. A cow’s udder has four teats, although twin births in cattle only about five percent of cases occur. In many animals has shown the nature of quasi-generously in favor of an additional pair of teats. In principle, however, is a minimalist principle in the evolution of living beings: wasted “Nature does not like,” says Wenisch. If only one pup must be attended to, the body also no effort for the training of many milk glands operate.
For the even number and arrangement of the pairs of mammary glands is a fundamental principle of the anatomy is responsible: “Mammals have a bilaterally symmetrical body,” Wenisch said. The mammary glands develop from the paired milk bars on both sides of the body. Depending on the species arise from the teats. In many animals, with only two mammary glands, they are located between the hind legs. In humans and monkeys, they have experienced a between the front limbs. One characteristic that unites us with the largest land animal in the world, too, female elephants have two breasts between his front legs.
Tags: female breasts, mammal, milk glands, two breasts
