The year 2012 is the 50th anniversary of the very first silicon breast implant. It was performed in Houston Texas, and Timmie Jean Lindsey still has the implants. Even though they have ruptured, she doesn't want them removed. But aside from how a breast looks, one of its main functions is to feed the newborn child.
As you would expect, all mammals (not just humans) have mammary glands. In the human, boys and girls have identical mammary glands until puberty, when the hormones make them change shape.
Humans are the only mammal in which the females develop breasts at puberty, and then keep them for the rest of their lives — regardless of their reproductive or lactating capability.
Looking at non-human mammals, the female Rhesus macaque monkes produce different milk for their sons and daughters.
The boy monkeys receive a more concentrated milk, so they spend less time with their mothers, and more time playing and exploring. These skills will be useful when they leave the group.
The Rhesus macaque monkey mothers make a milk for their daughters that is less concentrated, but still provides the same nutrition because they produce more of it. As a result, the daughters have to hang around their mothers for more frequent feedings — and this helps consolidate their matrilineal society.
Getting back to humans, there's an advantage to breastfeeding for the mother. Back in the Renaissance, the doctor Bernadino Ramazzini was the first to note that breast cancer occurred more frequently in nuns than other women.
Today we know that if a woman delivers and breast feeds her first child before she is 20, she has about half the risk of breast cancer than either a mother who had her first child after the age of 30, or a woman who has never had a child.
But breastfeeding has another effect upon the mother. It relates to that old saying in North America: "Never get between a mumma bear and her cub".
Bears will defend their young ferociously — as will macaque monkeys, rats and mice, prairie voles, hamsters, lionesses, deer, cats, rabbits, squirrels and even sheep. In mammals this is called 'lactation aggression' or 'maternal defence'.
And according to research by Dr Jennifer Hahn-Holbrook and colleagues, human mothers can now be added to the list of lactating aggressors.
She found that breastfeeding mothers were about twice as aggressive than either formula-feeding mothers or women who had never been pregnant. And just like non-human mammal mothers, they were aggressive with a cold calm. Their blood pressure rose less (under the same aggression-inducing circumstances) as it did for the formula-feeding mothers.
Dr Hann-Holbrook speculates that in the ancestral past, this aggression may have deterred predators. The breastfeeding mothers wouldn't place themselves or the infants in harm's way, but if attacked would defend themselves vigorously and aggressively.
Even today, breast milk is still surprising us. The molecular biologists, biochemists and geneticists who attended the 15th meeting of the International Society For Research In Human Milk And Lactation in Lima, Peru, had plenty of bombshells.
For example, I always thought that breast milk was served up to the baby sterile — with no bacteria in it. But it turns out that up to 600 different species of bacteria can be cultured from one single sample of breast milk. It seems that breast milk is similar to a complex cultured yoghurt, in the sense that many different species of bacteria are doing stuff we still don't understand.
Another major surprise is about the nutrients in breast milk. Basically breast milk contains fats (about 4 per cent), proteins, carbohydrates and a whole bunch of other stuff. The other stuff includes vitamins A, C, E and K, as well as some essential minerals. Besides the well-known lactose (a carbohydrate), there are also some mysterious oligosaccharides. (Oligosaccharides are also carbohydrates, and are made of short chains of various sugars joined together). On a percentage basis, there is roughly as much oligosaccharide as there is protein in breast milk. Not all mothers make the same set of oligosaccharides, but we do know that they tend to vary roughly following the mother's blood group.
Now here is a very weird thing. The baby cannot digest these oligosaccharides — so why are they there?
Perhaps they are there to feed the rapidly changing populations of bacteria in the baby's gut. At this stage, we simply don't know. What we do know is that they won't put the babies off the breast milk.