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that out of the way, it’s worth exploring briefly how the evolutionary zinger of lactation came about.
    As wondrously unique as human breasts are in their pendulosity, their basic glandular architecture is shared by all other mammals. Our packaging is just more fetching. Other mammals have some notably oddball features. The manatee has nipples under her flippers. The nipples of the aye-aye (a small primate) sit near the mother’s rear end. The gelada monkey’s nipples are so close together that the baby can suck both at once. Spiny anteaters and platypuses, rare egg-laying mammals, have no nipples, but they “sweat” milk to the puggle in their pouches through special glands. I don’t know what a puggle is, but I want one. A hedgehog-like mammal from Madagascar takes the trophy for most nipples, twenty-four, and theVirginia opossum is unique in having an odd number, thirteen. The only male animal believed to lactate is the Dayak fruit bat, but even that is somewhat contentious—it’s unknown if the substance has any nutritional value.
    But we’re more alike than not. Evolutionary biologists point out that the six thousand or so genes governing lactation are among the most strongly conserved ones we have, meaning they haven’t evolved as recently as genes governing, say, hair or toes or the ability to digest Cherry Garcia ice cream. We have protected our primitive lactation genes because they have served us so well. If the ability to lactate is among our most valuable genetic assets, the fat globule is its crown jewel. At its core, lactation is a fat-delivery system, very little changed over millions of years, except for some dietary tweaking. Each mammal has its own proprietary ratio of fats to carbohydrates to proteins. Human milk, for example, contains one-sixth the protein found in that of the quokka (a small marsupial), and one-fiftieth the fat found in seal milk.
    All mammary glands, ours included, serve four basic eon-tested functions: First and most obvious, they provide specialized, highly adapted chow for each little newborn mammal. Second, they provide immune support for same. Third, getting a little more subtle, they produce hormones that work as natural contraception, ensuring that a mother’s births are spaced adequately apart. Finally, they provide a “window of learning” in which young mammals can focus on acquiring skills rather than desperately seeking breakfast. (Note: attracting the opposite sex was never part of the original job description.)
    If it works, don’t fix it. And for millions of years—even hundreds of millions of years—it worked unbelievably well. In fact,mammals’ ability to lactate was crucial to our success. It was an innovation that changed the world.
    The earliest lactating species showed up at the end of the Triassic, about 220 million years ago. Before that, animals popped out of eggs and then immediately had to find food. It was rough out there. Dinosaurs ruled the earth. By the start of the Cretaceous, 135 million years ago, dinosaurs and giant sea monsters still held dominion, and the few mammals scampering around were small and rodent-like. But around 60 million years ago, at the beginning of our Cenozoic era, some very dramatic things happened to the earth’s temperature and moisture levels. Maybe a meteor hit the earth; maybe a volcano erupted; maybe the climate simply hiccupped of its own accord. Whatever it was, nearly 40 percent of all creatures went extinct in pretty short order. Dinosaurs? Kaput. Sharks and large marine reptiles? For many, ditto.
    The new world order was cuter and furrier and made up of strong social bonds, a keen sense of smell, and a lot of snuggle time. Mammals owned the Cenozoic.
    The dramatic emergence of lactating species has been something of a thorn in the side of Darwinians, who had a hard time explaining it. Critics of evolution like to point to lactation, along with the development of eyes, as events that couldn’t simply