Breasts by Florence Williams Read Free Book Online

evolve gradually, by accidental mutation, in a way that conferred an immediate survival advantage. How could you have a partial eye or a partial teat? Darwin himself went out on a limb to speculate that mammary glands slowly evolved from sweat glands in brood pouches where some fish and other marine animals kept their eggs. The sweat gave the eggs a little extra nourishment, and the system was off and running.
    It turns out that Darwin hit pretty close to the target. At least so says Dr. Olav Oftedal, the closest thing the planet has to an expert on the evolution of lactation. Oftedal came to his specialty in a circuitous way. The child of a Norwegian diplomat, he grew up chasing snakes and playing in the hardwood forests of Europe and the United States. But in the late 1960s, wanting to be socially relevant, to change the world and improve infant nutrition, he started working for aid programs in the developing world. Oftedal grew discouraged with the pace of policy work, though, and went back to school to study maternal-offspring nutrition, this time in the animal kingdom.
    “It was amazing how Darwin hit on things, and this was before genetics!” boomed Oftedal from his office at the Smithsonian Environment Research Center near Chesapeake Bay in Edgewater, Maryland. Oftedal has built his three-decade career studying the remarkable lactation habits of seals, bears, bats, and monkeys, among others. Weddell seal pups near Antarctica must quadruple their weight in the first six weeks of life, so seal milk is around 50 percent fat, among the fattiest known. A stiff wind might turn it into butter. Lactating seals have unique feeding pressures; in some species, the mother nurses for a few days, then takes off for days or even weeks to replenish her body stores far from home. The pup has to wait for her return.
    Oftedal has tasted this wondrous seal milk, declaring it “fishy.” You might think obtaining a sample is no simple matter, and you’d be correct. He throws a rubbery bag over the mother’s head, and then pumps her teats with a handheld device—all in temperatures around 20 degrees below zero Fahrenheit.
    Oftedal sees lactation as a quintessential competition between mothers and offspring for nutrition. In the case of the Weddellseal, the mother is nearly depleted by the needs of her fast-growing pup. Seen in this light of tremendous costs, lactation wouldn’t have evolved if it were not very, very useful. It also necessitated radical innovations in both the mother’s hardware and that of her young, including different teeth and brains. It was not to be embarked upon lightly.
    First, we had to figure how to make the hardware, the mammary gland itself. Teeth, oddly enough, offered a blueprint. Having developed much earlier, they pioneered a technique for simple bioorigami, showing how two layers of tissue could fold in on themselves and make proteins to build an organ. In a sequence that would make dentists everywhere happy if they knew it, we would never have breasts if we didn’t have teeth. But it was still a long way to get from a molar to a milk machine.
    For one thing, we had to keep upgrading the software. Metabolic activity is regulated by hormones that flow back and forth from the brain to target cells all over the body, including the mammary gland. As mammals evolved, so did the complex hormonal conversation necessary to regulate their changing bodies. Mammary glands evolved receptors on their cells to “listen” for and collect estrogen, progesterone, prolactin, lactogen, and many other hormones. These tell the glands when to mature and when to regress. They reveal when there is a fetus in the oven, when to deploy a glandular growth spurt, when to shut down milk production, even what sex the fetus is in order to fine-tune the composition of the milk.
    “We don’t realize how strange mammary glands are,” said Oftedal. “There are tons of placenta-type structures out there in sharks and lizards, but