Are three breasts better than two?

As we all know, toddlers like to switch sides when nursing--sometimes to the point of driving Mummy mad. Why have one breast when you can have two? Little Seal, however, seems to feel that even two breasts are not enough--she not only switches from right to left incessantly, but has also developed a bizarre habit of rooting around in my armpit and screaming in protest at the fact that I don't have another mammary gland for her under my arms (what a mean Mummy).

One day recently when she did this, my mind suddenly flashed back to something I'd read a while back about how a lot of women have rudimentary breast tissue in the underarm area, which is why swollen armpits are common when your milk "comes in." A google search soon plunged me into the bizarre world of multiple breasts.

Turns out the swollen-armpit thing is just the tip of a large and varied iceberg. Somewhere between 1% and 6% of all women have some degree of supernumerary breast tissue. In most cases (polythelia) this is just under-the-surface tissue, but in more extreme cases (polymastia) you have actual nipples as well--sometimes forming very noticeable extra breasts. These are most often found along the "milk lines"--pathways stretching from the groin up into the armpits. Litter-bearing mammals, of course, normally have milk-bearing teats up and down these lines; at some point in the evolutionary process our mammalian predecessors lost all of these except two. Charles Darwin considered the appearance of multiple breasts in humans to be an example of atavism--the survival or reappearance of a primitive trait in a more "highly-developed" species, like, for example, the occasional human baby that is born with a tail. (Could Little Seal's armpit-rooting be a kind of vague instinctive memory left over from the time when our furry ancestors actually had functioning breasts going up and down their abdomens? Who can say?)

The "throwback" theory is lent credence by the embryonic development. One of the eeriest things about pregnancy is the way the embryo's development over the weeks and months seems to repeat evolutionary history in miniature--the unborn child develops a tail which then falls away, and later grows a coat of fur which is then shed and reabsorbed, and so on. Over the first couple of months, "milk lines" in the fetus develop into mammary ridges, but in around the ninth week all these ridges recede and disappear except for the two which later become the "breasts" we are familiar with. In a few embryos, presumably, the surplus ridges do not fully disappear and instead continue to develop into rudimentary breasts. The atavism theory has appeal, but it doesn't seem to fully explain the extra-breast phenomenon, given that such tissue can also appear outside the milk lines--on the legs, in the groin and even on the sole of the foot.

As I mentioned above, it's not unusual for women to report swollen armpits at the very start of breastfeeding, and droplets of milk leaking from the armpits are far from uncommon (judging from all the questions on Yahoo Answers--that perennial mecca for people with weird and embarrassing body-related questions). In extreme cases, extra breasts have been known to have fully functioning nipples and produce useful amounts of milk.

An often cited case from 1827 refers to Therese Ventre of Marseilles, France. Her mother had a supernumerary breast beneath her normally positioned right breast. Ventre had a supernumerary breast beneath her normally positioned right breast. Ventre had a supernumerary breast on the side of her left thigh. This breast enlarged during puberty, and when she became pregnant, it produced milk. It was offered to her infant who took it willingly. She apparently nursed five children during her life from all three of her breasts. (Southern Medical Journal Supernumerary Breast Tissue: Historical Perspectives and Clinical Features, Department of Pathology and Laboratory Medicine, Emory University School of Medicine)

In our own time, however, extra breast tissue is more likely to cause issues with breastfeeding. In several cases, women presenting with swelling under the arms have had the sites biopsied, only to reveal that the lump is merely extra breast tissue and that milk is now leaking uncontrollably from the site of the biopsy--a "milk fistula." Breastfeeding Materials advises that such milk is likely to dry up on its own, just as any milk supply will ultimately dry up if there is no suckling; however, in this case here, the mother's milk fistula did not cease until she finally weaned her baby. Presumably, her accessory breast and normal breasts had enough tissue in common that they shared the same feedback mechanism, and stimulation of the regular milk supply thus tended to stimulate the milk production in the armpit as well. Who knows? In any case, the good news is that this troublesome extra tissue was removed through surgery, leaving the mum free to nurse her future babies if she wanted.

Supernumerary breasts have, in some historical periods been associated with witchcraft--Anne Boleyn was rumored to have one, although that may say more about Boleyn's enemies than about Boleyn herself. In other times, extra breasts have been considered a sign of super-fertility (think of all those multi-boobed goddess figurines), but there's no evidence of this. On the contrary, there is some evidence linking extra breasts with elevated rates of certain congenital problems, especially abnormalities of the urinary tract such as "supernumerary kidneys, failure of renal formation, and carcinoma of the kidney."

So while the image of being able to feed a baby from multiple breasts is appealingly bizarre, it seems fair to say that in the real world, three breasts are definitely not better than two. Although most nursing toddlers and babies would probably disagree with me about that.