Tag Archives: evolutionary biology

Geeking Out on Mothers’ Milk

Debbie says:

One of the many good things about Nicholas Day’s article in Slate about the science of breast milk is that, pretty close to the beginning, he goes out of his way to say that “conversations about lactation always seem to require disclaimers,” and his is that lack of breast milk

has never been a death sentence. Hundreds of years before halfway-decent formula, infants were fed gruesome substitutes for breast milk (mushed bread and beer, say)—and although many more died than those who were nursed, many also survived. So the lesson of the new science of milk isn’t that formula is some sort of modern evil. (It isn’t modern or evil.) It’s that milk is really complicated—and evolutionarily amazing.

Of course, this is important because of how intensely mothers (at least white, middle-class American mothers) can blame themselves if they can’t nurse or don’t like it or don’t do it for two years or whatever the current thinking is. In my history, the story was the opposite: my mother wanted to nurse and it was thoroughly unfashionable. Her doctor wished her well but said, “I can’t help at all; I don’t know anything.” And nursing is, contrary to many people’s beliefs, often neither simple nor intuitive. So when she ran into trouble, she went to the African-American women waiting on the corner for the bus to take them (to? from?) their jobs as maids (this is Baltimore in 1951) and got their advice. I’ve always admired that–and wondered why she didn’t ask her own mother, who almost certainly nursed all three of her children.

But I digress.

In the article, Day relies mostly on the work of Katie Hinde, a Harvard assistant professor who studies breast milk in humans and rhesus macaques, and writes an occasional blog called Mammals Suck … Milk (Day shortens the name, which I think is a pity). According to Hinde, breast milk is not very well understood. L. Bode at the University of California San Diego recently published a paper demonstrating that some of the carbohydrates in breast milk are indigestible by babies … instead, they feed the bacteria in the baby’s gut, and perform a wide variety of health protection tasks in the process.

Hinde, whose field is evolutionary biology, focuses more on what she calls “milk as signal.” In rhesus macaques, “The composition of early milk seems to mold infant temperament. But—and here’s the twist—the males were much more sensitive than the females. Roughly, the more cortisol, the more bold and exploratory the male rhesus macaques were.”

Although evolutionary biology is a more sophisticated and scientifically defensible field (by far) than evolutionary psychology, nonetheless this is probably very simplistic gendering and might not withstand a more nuanced examination. There is so much data, beginning with the now almost 15-year-old Biological Exuberance, undermining binary descriptions of animal sexual/gendered behavior that I can’t trust statements like:

In rhesus macaques, daughters stay in their social groups their whole lives,” Hinde notes. “They form a bond with their mother that only ends when one of them dies. So it might be that mothers are nursing their daughters more frequently and that helps establish this bond.” In contrast, the sons end up leaving the group—and fattier milk means they nurse less often, which means they can spend more time playing with strangers, developing skills they’ll need later in life. The milk, in other words, reflects and cements the social structure of rhesus macaques.

And, of course, Day (if not Hinde) feels perfectly free to hint that these findings will illuminate human behavior.

Nonetheless, there’s more in the article about the complexity of the content of mother’s milk, and the whole thing is worth reading. I only wish that, as a culture, we were able to extend our observation of chemical/biological/hormonal/tactile substances and experiences that we know we don’t understand without trying to fit them into our extremely reductive concept of two immediately identifiable, vastly different, and non-overlapping genders.

Thanks to boingboing for the pointer, and to whatever link list got me to boingboing to find it.


Do Men and Women See Junk Science Differently?

Debbie says:

I’ve gotten to the point where I can sense junk science from miles away, which is what happened when I saw this news article about “how men and women see the world differently.”

My first clue was the fact that the study looks for a gender differentiation where there’s absolutely no evolutionary or biological reason to have one.

My second clue was the study’s conclusion:

“…men have greater sensitivity to fine detail and rapidly moving objects, while women are better at distinguishing between colors.”

This result is so perfectly aligned to simple gender binary expectations in the western world in the 21st century that it smells like the researchers found exactly what they were looking for.

Given these two clues, I went hunting. Here’s the abstract, from the Biology of Sex Differences journal (another bad sign). What I love about the abstract is this sentence, “We tested large groups of young adults with normal vision.” Most abstracts give sample sizes. When this abstract just said “large groups,” my spidey-senses tingled even more than they had already. Fortunately, the abstract takes us to a .pdf of the draft paper (this research isn’t even finalized, it’s just making the science news, because science news loves gender differentiation).

On page 7 of the .pdf, after a lot of technical explanation of why they believe these sex differences exist and how they set out to find them, we find the sample size. Want to guess? “Large groups” should be probably at least 1,000 (that would be a reasonable number for a single “large group,” at least).

Okay, here we go: 36 females and 16 males. No, really. That’s a “large group” for dinner, but not for much else.

Note the disparity between females and males. Since all subjects were volunteers, it sounds to me like more women volunteered than men, and the scientists decided that that wasn’t a problem. So if you have more than twice as many women as men, and you’re looking specifically for differences between women and men, wouldn’t you wonder whether your group of women was going to show wider variation than your group of men, just because of sample size? I would. But they don’t even acknowledge this; they just go blithely on, after saying that the smaller number of men reflects the demographics of the college where they were doing the research (perfectly plausible) and that they rejected all men with anomalous color vision.

Finally, on page 16, they trot out the old and long-debunked “hunter/gatherer” explanation. You see, men are hunters, so they have to be able to make fine movement distinctions. Women are gatherers, so seeing colors helps us find the right crops (and accessorize!). As they have not bothered to find out, this has not been the thrust of anthropological and paleontological belief for some time now (here’s one resource). Besides, fine movements are not how big game is tracked.

Once again, a little research establishes that if men and women actually see differently, these researchers haven’t proved it. And they know it, or they wouldn’t be so cagey about hiding their sample size.