Breasts by Florence Williams

Breasts: A Natural and Unnatural History by Florence Williams


Human breasts are made of three kinds of tissue: milk-producing glands, fatty (adipose) tissue, and connective tissue containing collagen.


Three functions of mammary glands:

  1. feeding babies,
  2. immune support for babies (colostrum),
  3. delaying subsequent pregnancies.


Mammals evolved from therapsids, the first animals with hair follicles and mammary glands. Mammary glands evolved from sweat glands. Mammary glands first evolved for immune support. Baby brains need a lot of fat nourishment to grow, so women who don’t have much fat stop menstruating, so they won’t have babies they cannot adequately feed. Women store fat in their breasts and hips. Humans need to store more fat than other primates, because we don’t have fur to keep us warm, and we need to burn the fat to generate internal heat.

Range of Motion

There is a debate between male and female scientists regarding the importance of breasts as sex signals, with men favoring this explanation. Women scientists prefer theories that emphasize breast function rather than appearance. Breasts give the nipple more range of motion that it has in the other primates, which are flat chested. This range of motion makes it easier for the baby to feed when being held in a wider variety of positions.

Early Menarche

In the United States during the past few decades the onset of puberty has been getting earlier and earlier in girls. The cause is unknown, but better nutrition is probably a major factor. Many young girls become pregnant before their pelvis is large enough to permit the passage of the baby.

Baby Formula vs. Breast Milk

A Swiss fellow named Henri Nestlé developed baby formula in the late 19th century. It gained in popularity during the early twentieth century. The return to breast feeding began with the La Leche League, which was founded in the 1950s in Illinois. In the third world there are problems with formula, because it is often made with contaminated water. Breast feeding is harder on the mother, but it is better for the baby.
Breast milk contains many good bacteria for the baby’s intestinal tract. It also contains oligosaccharides that feed the bacteria in the baby’s intestines and prevent bad bacteria from growing in the baby’s intestines. Breast milk is especially good for premature babies, and helps prevent necrotizing enterocolitis.Breast milk contains lactoferrin, which binds iron, and thus killing pathogenic bacteria in the baby’s gut that need iron to live. Breast milk also contains a complex between alpha-lactalbumin and oleic acid called HAMLET that helps kill tumor cells and reduces the incidence of childhood cancer.

Vaginal Delivery vs. C-Section

The transfer of good bacteria from the mother to the baby is also helped by a vaginal delivery, as opposed to a C-section.

Jaundice and Mastitis

The author describes her own nursing experiences. One frightening episode was when her baby turned bright orange, because her son was suffering from breast milk jaundice. Jaundice results when the liver has trouble converting bilirubin to a form that can be excreted in the urine. It causes yellow skin and also the whites of the eyes to become yellow. It is a serious condition in a newborn. She immediately took her baby off the breast. He was treated by phototherapy, which converted the baby’s bilirubin to a form more easily excreted in the urine. The author also experiences several episodes of mastitis. It is caused by cracked or clogged nipples and is treated with antibiotics. She also employed the services of a lactation consultant.


When women become pregnant, the milk glands in there breast become more developed. After they finish nursing the baby, their breasts undergo a process called involution, where the milk glands recede. Women who have children when they are young are less likely to develop breast cancer.


Xenoestrogens are non-steroid molecules that mimic the role of the estrogen hormone in the body. There are both artificial xenoestrogens, often occurring is plastics, and natural xenoestrogens produced by plants, called phytoestrogens. Phytoestrogens may have evolved to protect plants from herbivores, by reducing the fertility rates of males that eat them. There are also many other synthetic chemicals in our environment that accumulate in the mother’s fat and then are passed on to her baby in her breast milk. During the last several decades there has also been an increase in the rate of breast cancer. Whether the artificial chemicals passed onto the baby in breast milk are a cause of this increase in cancer rate is a subject of debate among scientists.