So, let me answer more openly the kind of questions I got privately.
I had been under the impression that some diseases were more common in some races than others largely because of biology. I also know that culture plays a huge role in terms of lifestyle behaviors that impact health, access to healthcare, poverty, etc. But I thought people of different races actually were biologically and genetically different, at least on some things. Could you please help me understand?
It's a tough set of concepts to get the mind around (remind you of another topic?). I've just had time to get used to it.
For those of you who have met me or seen a picture of me, most will have experienced me as "white." The reality is that ALL of my maternal relatives are "black." 50% of my genes come from people identified as African Americans (wait: there was a great great great grandfather who was reportedly Jewish, from Jamaica).
But what about diseases like Sickle Cell Anemia? In terms of screening, my risk is as high as anyone you meet on the street with darker skin. In truth, I have zero actual relatives with sickle cell and probably had zero risk of sickle cell not because of my 'white' relatives but because none of my known maternal line has sickle cell. Being of African-American parentage doesn't make me related to all other black people.
Keep in mind we're throwing an ENORMOUS group of unrelated families into one pool and a small percentage of those families are genetic descendants with that mutation. That small group of carriers don't actually affect those other darker-skinned people's risk of sickle cell. On a public health scale the statistical numbers are meaningful, as screening is a large-scale activity. But in the actual genetic reality two black people are not particularly likely to be related and the part of their genetics they share (relative skin color) isn't likely to be from common lineage. Skin color is not connected in any meaningful way to any other genetic traits. If you look at the world population you'll see all variations of light and darkness and hue with wide variety of hair texture, eye color, facial features and patterns of disease. Color is a melanin thing - how close one's far, far antecedents lived to the equator and their adaptive risk for sun exposure.
A random Italian and a random Norweigan - both "white" - are unlikely to be related. But two Missisippians of any color ARE because the races mixed routinely for hundreds of years. It wasn't always voluntary, of course, but there you are.
it's a melanin thing mix over generations.
American 'black people are almost always a wild melange and their actual skin color bears little relationship with anything. It would seem intuitive to think that it is a matter of dilution and strengthening of genetic relations but it isn't. Far more like eye color, which we largely disconnect from racial origin AS LONG AS SOMEONE IS "white." We don't think of blue or brown eyes, for example, as some sort of genetic tracer and feel some kindred spirit between fellow-Hazel eyed folk. But because racism and class and that Peculiar Institution (slavery) has caused us to think of all people who are discernibly descended from enslaved people as all in one group we consciously forget that all of the "black" and "white" children of a slaveowner equally share in his genetic background. We also try to forget that the reason black folk tend to marry black folk is largely cultural - they're not choosing on the basis of genes and not necessarily mixing the same family lines. I did not know my white relatives as they wanted nothing to do with us - but I did know my black mother's family very well and was more likely to spend time with black people and, eventually, date and have children in that community. Racism has kept races in the same neighborhoods and jobs and churches in the US, in general, folding the mixed kids in with the so-called black folk as if they were more related to them than the white relatives!
Another amusing thing about race is that our cut-off is at visible color. That means anyone with any discernible melanin that isn't fobbed off as "ethnic" is in the same basket. As if there was something holding all those from 3-10 on the color scale (making that up) together and excluding the 1-2s. But we are so used to using ANY color as an inclusion concept that we've come to think it has some biological meaning. It doesn't.
Fun historical artifact: my birth certificate says "negro" (it was 1961). It was illegal at that time for my parents to marry in some states.
But I am just as much my mother's as my father's child, genetically. If I had married a discernibly dark-skinned person our genetic kids would be considered "black" by virtue of melanin and culture. But if I was "black" appearing and had genetic babies with a "black" partner is that somehow different? How many white relatives does it take to make you not black any more? How diluted is non-black? You can see how the "stain" theory is absurd - the "one drop" rule as they used to call it. But there is no "stain" of lack of melanin, I notice.
Is there some quality genetically that carries with the genes for skin color? Nope. Not one.
It is our cultural frame for race that confuses us. Our belief that any visible melanin is a sticky stain that carries other things comes from our sense that African ancestry is some sort of common "other" with more than 50% influence over a baby. Really, the only stain is that concept.
P.S. Bi-racial kids are not cute. Being bi-racial is not like being a puppy mixed with a kangaroo: our parents are the same species and 99.9% the same. There's no reason why being bi-racial makes someone cute. Although of course *I* am adorable, personally.
P.P.S. The term bi-racial is ridiculous. It breaks the rule I just discussed. And yet, I find the alternatives awkward and forced. Sigh. P.P.P.S. Interesting editorial today in SciAm on this topic: when should medicine talk about race?