A Brief History of Breasts
Reading Time: 5 minutesAt 35, I Grew Breasts—Thanks to Hundreds of Millions of Years of Evolution, We’re going back to the Triassic., Boobs: The history of breasts is beyond what you can imagine.
Boobs are back. Also, they never went away. This is part of Boobs Week—read the whole thing here.
Breasts are usually not the first thing we notice on an elephant. You might have never noticed them at all. But among female elephants who have recently birthed a calf, ears are not the only parts that hang low and wobble to-and-fro. Yes, although we haven’t shared a common ancestor in more than 66 million years, mother elephants and about half the human population have a delightful feature in common: a set of tits.
While breasts are only found among mammals, most mammals do not have breasts. (The duck-billed platypus doesn’t even have nipples or teats; it oozes milk, kind of like how you sweat, that its young lap up.) Specialized protruding tissues to feed growing offspring that exist in multiple pairs along the abdomen are common. But whether we’re talking about the spots where kittens latch on a mother cat or a bovine’s udders, these setups are not typically very breast-like. Unless you’re at a furry convention, I doubt you’re going to have much reason to say ‘Look at the breasts on that cow!’
But a few kinds of mammals, like our elephantine friends and our fellow primates, have arrangements of mammary tissue on the chest. In our own species, breasts are made of fatty, glandular, and fibrous tissue that is internally crisscrossed with ducts and sits on top of the chest muscles. Despite the fact that they are often considered a binary sex characteristic, anyone past puberty can have breasts.
Now—some might object to calling elephantine mounds breasts. In nonhuman animals, milk-producing structures are, scientifically, mammaries. But I would say breasts are really about shape, placement, and a shared evolutionary lineage. There’s a lot to be gained by calling a breast a breast, whether it sits on a human chest or droops between the legs of a larger creature. We can learn more about our own selves through what commonalities we share with other life on Earth, rather than carving out another way for Homo sapiens to be different, even when it comes to this small—or, as it were, sometimes large—bodily feature.
The origin story starts with feeding youngsters. Precisely when in prehistory mammals began to lactate, no one yet knows. Body fluids and soft tissues (boobs; butts) are not treated kindly by the fossil record. One possibility is that protomammals of more than 225 million years ago exuded a protein-rich milk-like substance from a gland on their bellies to keep their thin-shelled eggs moist while on dry land. The fluid would have had the additional benefit of nourishing the hatchling mammals once they broke out. It’s something life has evolved to do time and again. Consider that today amphibians, birds, and even spiders make their own forms of milk. Mammals have taken the evolutionary specializations further (and, given how evolution often nudges different animal groups to take similar forms to accomplish similar tasks, it wouldn’t be altogether surprising if millions of years from now some of the crawly or feathered creatures develop their own sorts of mammaries).
Some mammals, though, would take this extra nutrition up a cup size. Over time, ancestors of marsupials, like kangaroos, and placentals, like us, evolved nipples to make delivering milk a bit more on-demand and precise (the act of suckling has in turn shaped mammal skulls through time). Given that many mammal species have litters, many nipples were required to nurse rapidly growing beasts in a world still full of strange, often immense reptiles.
We actually retain the vestiges of the ancient pattern from a time when our distant ancestors, perhaps in the Jurassic, raised many brand-new offspring at once. An anatomical study a few years ago found that eight pairs of small fat mounds run along the human torso on what developmental biologists call the ‘milk line.’ The mounds often had extra hairs or moles, suggesting that these fatty spots are a form of vestigial breasts. The reason these bumps are vestigial, and I’m not shopping for a bra with six cups, has to do with changes among our prehistoric primate ancestors. When early primates stopped having litters and instead had just one or two offspring at a time, all this tissue to deliver milk was an incredible waste of energy. It’s easy to see why a mutation that shut off breast development after one pair presented an advantage.
A group of mammals called tethytheres went through a similar change. The large members of this mammal group usually gestate a single offspring for a long time, and so their anatomy, like that of primates, also shifted to deliver milk in volume through two nipples instead of rows of many. The cleavage of elephants, manatees, and perhaps even the extinct, dual-horned Arsinoitherium evolved breasts not unlike ours.
Out of all this deep prehistory, though, humans have once again turned out to be strangest of all. (The fact we stand upright without tails would, alone, be nonsense enough.) Unless there is a strikingly stacked species of mammal out there no one has seen yet, humans are the only living creatures we know of to have permanent fatty breasts. The mammary tissues of other primates, and of tethytheres, inflate and become prominent with lactation; while breasts in humans do swell when there’s a baby to feed, even those of us who are not parents to little ones have a need for sports bras.
Why humans have breasts with staying power, we’ll probably never know. The hypothesis I like best involves hormonal shifts in our ancient human ancestors that favored new deposits of subcutaneous fat for storing energy and regulating body temperature. Mammary and chest tissues were one of those places where fat packed on, a happenstance of physiological changes—setting us up to variously be entranced, upset by, and otherwise feel conflicted about breasts through history. Our feelings about breasts vary culture to culture, and across time, which suggests that the permanent fatty orbs are more likely to be a curious side effect of other evolutionary changes rather than the result of sexual selection. We feel so many ways about breasts today; our ancestors probably had a variety of attitudes, too.
For myself, I’m enthralled by the fact that anyone can grow their own breasts. Today, the genetic and developmental possibilities for permanent breasts reside in our bodies, waiting for their cue, no matter our sex or gender. I grew my own after starting hormone replacement therapy at 35. I felt like the estrogen I put under my tongue every day was taking its sweet time while I was checking my chest every day, just as Jeff Goldblum’s Dr. Brundle in The Fly peered in the mirror to assess the changes to his skin. I even made a photo album in my phone to track my growth. The mild pains of growing breasts were offset by the joy I felt at seeing my shape change. I was so enthused by the shift that—as my girlfriend will never let me forget—I would absentmindedly rub my sore breasts while out and about during the day, lost in the happiness that I had breasts to rub at all. I would eventually ask a surgeon to give me a little more heft, yet I couldn’t be anything other than amazed that a hormonal tweak could call out something so ancient in my flesh. I was thrilled that my body immediately knew how to respond to the increased estrogen, an ancient and shared pathway that changed how I felt about myself as much as it did my silhouette.
Reference: https://slate.com/technology/2024/08/breast-evolution-elephant-platypus-milk-mammals.html
Ref: slate
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