Saturday 8 October 2011

There Is Only One Human Race. Part Two of "The Evolutionary Biology of Race: Are There Human Races?"

Many people would respond to the above statement with guffaws. Most would say, ‘But surely, Rob, you look different from Will.I.Am or Bobby Jindal! And we know that those differences are the result of heredity.’
    And, on the surface of it, they’d be right. But that doesn’t mean there’s a biological basis for race—only that there’s a biological basis for the genetic variation exhibited by Will.I.Am, Jindal and Gargett, and that the perceived differences are inherited traits. Thus, the core of my argument is this: biology is a necessary, but not a sufficient explanation for what people think of when they talk about race.
     In the remaining installments of "Are there human races?" I want to talk about several subjects that have a crucial bearing on the question. The first has to do with the nature and sources of human genetic variation—I’ll want to tell you about biological races and how that concept fits with our understanding of the human species. Next I’ll want to talk about the sources of the superficial differences attributed to different racial categories—in other words, microevolution in humans. Next I want to talk about the human genotypic variability—and about the inability of racial categories to account for the genetic variability that escapes the scrutiny of those with a racial worldview. I’ll probably want to explain how the fossil record fits into the debate, because there are still some unreconstructed anthropologists who maintain that the differences we see in human groups today have a long evolutionary history.
Humans are hairless, bipedal apes (copyrighted photo from the Eyewitness series)

More after the fold...
Human beings are large mammals, members of a group of the most complex animals on earth—the Primates, specifically the apes. Homo sapiens is a geographically widespread, polytypic species. This means that, when you look at a cross-section of humanity, you'll see differences, just as you do in similarly widespread species, whether primates or other animals. These differences can be related to the environment, as with skin colour, or to genetic drift, an evolutionary force that creates change by dint of chance acting on genetic variants. However unlike lizards, or birds, that have been observed to speciate under certain conditions, modern humans have never been truly isolated by geography. Because of that, it's impossible to imagine that we might consist of races in the biological sense.
     Here’s why.
     We form a geographically continuous, interbreeding population, which means that a strictly biological definition of race will never work. Biological races only occur when discrete populations of a once-continuously distributed species become isolated by geography. This can happen, for example, when climatic changes create barriers between two or more populations of a species.
     When this happens, the forces of evolution naturally result in differences that will probably include outward physical differences, but which may, eventually, result in reproductive isolation. This has occurred when two members of what was once a single species no longer recognize each other as potential mates, or as, in the case of horses and donkeys, where they might think they can mate, but that there has been sufficiently long separate microevolution to mean that they are biologically incapable of producing fertile offspring most of the time.
     Humans are not like that. The only thing keeping some humans from interbreeding with other humans is just the sort of thing that I'm talking about—racial or other social categories that prescribe those with whom it's appropriate to mate.
     So, if we don't comprise truly biological races, what allows us to perceive differences that we have traditionally called races? I'll want to examine those perceptions, to tease out what’s really being seen as difference. But before I do, I need to talk about microevolution.
     When your parents conceived you, each contributed an equivalent amount of DNA to your genetic makeup. Go back one generation. Your four grandparents contributed 1/2 of their genes to your mother and father's genomes (1/4 each to yours), and so on back down your family tree (I've always thought this generational progression resembled the roots and not the above-ground parts of the plant—but there you go). Your genetic makeup, therefore, is the result of evolutionary changes in thousands upon millions of generations of sexually reproducing organisms—all the way back to the earliest multi-celled organisms. In a very real sense, you and every other human, every other living thing, represent a unique end point of an evolutionary process that had its origins in the first life, several thousand million years ago. 
     With each generation, unique new combinations of genes, together with occasional non-lethal mutations, contributed to the appearance and physical makeup of the new organism. Under the right circumstances that new organism survived to reproduce, and contributed some of that new combination of genes to succeeding generations. It’s why you may resemble your parents to a degree, at the same time as you may have features that are new to your family, or that haven’t been seen for generations. This is what Darwin called ‘descent with modification,' which he intended as a concise description of biological evolution.
     Each person’s genetic makeup encounters the environment, and is more or less successful at coping with whatever life throws its way. For humans, success in the genetic sweepstakes involves not only the physical apparatus that enables us to find enough food, to stay alive, and to produce offspring, but also, unfortunately, our genetic makeup can predispose us to suffer the outrage of racism, if we happen to have the right combination of outward physical attributes. Heredity and genes may be the biological basis for the way we look, but biology is not ultimately responsible for the way we appear to others.
     That’s because the role of biology in producing humans of a certain type is moderated by our choice of mate. For many groups parents decide who mates with whom, and even though people in much of the English-speaking world no longer practice arranged marriages, don’t kid yourself—our parents still manage to involve themselves in mate choices, something I like to call 'approved marriages'). So now, I’d like talk about the sources of some of the superficial differences that are ascribed to racial categories.

What colour is ‘black’? (copyrighted photo from Time Magazine)
Whether we choose a mate ourselves, or they're chosen for us, the criteria employed in choosing them are seldom based in the ability to survive—often the criteria are fairly arbitrary, especially in today’s world. 

     For example, we generally mate with someone who speaks the same language, but obviously that has no real bearing on our ability to produce offspring. We also generally mate with someone who looks superficially like ourselves, which means that light-skinned people usually mate with light-skinned people and have light-skinned offspring. But there’s nothing necessary about colour coordination when it comes to making human babies, as everyone knows. Ironically, dark skin is useful in protecting an individual from the sun’s harmful rays, and therefore can have bearing on the ability to reproduce. However, notwithstanding the rates of skin cancer among fair-skinned people living in very sunny places, skin colour need be of little use from the standpoint of survival in today’s world. 
     Nevertheless, although mate choice criteria are in some sense arbitrary, we have still managed to prioritize our mate-choice criteria along some very definite lines. In the superficial characteristics one uses to choose a mate, we have tended not to worry about eye colour as much as skin colour, and  hair colour matters less than language, and so on. As we all know skin colour has, to this day, a great deal to do with the mate choice of a great many people (at least in some cultures, such as those that are descended from mostly Christian European emigrants). Mate choice, then, tends to be culturally prescribed, and to a large degree, the physical criteria one uses in choosing a mate are totally arbitrary.
     Until recently we were technologically incapable of basing our mate-selection on microscopic differences in our genetic makeup, which is why, for example, two people carrying the gene variant that causes sickle cell anemia often find themselves in the unfortunate situation of having offspring that die at an early age. Yet, even in this age of gene therapy and genetic testing of fetuses, most people choose mates on the basis of outward characteristics, and not on any unseen characteristics that could carry much more evolutionary weight than skin colour or the shape of the eyes.
     The point is that there is good evidence suggesting that the differences we have ascribed to racial categories are the result of what's called positive assortative mating, much like the selective breeding of domesticated animals—the differences are of our making, and based in culturally prescribed preferences. They tend, therefore, to follow national or ethnic or linguistic (and therefore cultural) boundaries.
     ‘Even so,’ some might say, ‘we must be perceiving real patterns within the variability inherent in the human genome, for us to be able to recognize something we choose to call races.’
     Let’s examine that premise for a moment. The characteristics we’re talking about—skin colour, for example—are not discrete categories. To get an objective measure of something like skin colour, a scientist would measure the amount of light that’s reflected by the skin, using special equipment, much as you would to objectively describe the colour of any object. Anthropologists use the skin under the arms, because that is usually the least affected by tanning. Using such methods you find that skin colour varies widely between the so-called races, but also within similarly defined groups. people from sub-Saharan Africa can have the same skin colour as people from South Asia. The point is that because skin colour can be seen to vary continuously, from albino white to almost jet black and everything in between, it's impossible to distinguish 3 or 5 or even 25 different skin colours. 
     So, you’ll notice skin colour doesn’t nicely adhere to the traditional distinctions. Skin colour grades from one area to another, from the equator to the poles, with the possible exception of Northern Europe where, in contrast to the rest of the world near the poles, it’s almost always raining. So, what is 'black' if not an arbitrary, culturally determined category, quite irrespective of the real appearance of those so labelled. And, surprise, surprise, the people with the darkest skin do live in the Deep South...of India! Gotcha!
     In a similar fashion, I can demonstrate that many of the traits used to construct racial categories, and the decisions on how to sort them, are arbitrary. And, as I will point later, the racial categories that we create ignore most of the genetic variability inherent in the human species, which belies the very categories we create.

This set of portraits is from a Time Magazine feature: "Lost Tribes, Lost Knowledge?"

Study these sets of photographs. You'll immediately recognize, in the people depicted in each set, features in common, and features that may differ from your own. This is a fairly straightforward example of the kind of comparison on which most people base their personal classifications of racial difference. Look more closely. How many of you have eyes the same colour as the people in this photograph? Some do; some don’t. For those of you who do, would you call yourself members of the same race as those people in the photograph? For most of you, the answer is no. How about hair? Same thing. I could go on. Some of you might have skin the same colour, but the nose isn’t right, or the hair's too straight. Yet, you might say, ‘It’s the whole package that’s important—on the whole they look the same. And therein lies the justification for the packages that I choose to call races.’
     That same person might say, ‘These people over here have brown skin, broad, flat noses, black hair, brown eyes, and so on.’ And that same person can see a distinctive suite of features in each group that might allow them to place these people roughly on a map of the world. If they’re reasonably geographically literate, they’d probably get it right. They’d get it right because there are geographically delimited populations of human beings that exhibit clusters of superficial, genetically determined traits, such as dark skin, broad flat noses, dark hair, dark eyes, et cetera—whether you’re talking about people on the Isle of Sky or the island of Flores. And, as I explained a bit ago, this has much to do with marriage and mate selection, with maintaining social coherence, and so on.
     So, given these perceived differences, and our evident ability to categorise people according to biologically based traits, why should I expect you, the reader, to believe that there's no biological basis for race? Easy.
     To start with, we need only look at the efforts made over the years to define races, and the utter hopelessness of such attempts to adequately characterize human variation in that way.
     But that'll have to wait for Part Three.

1 comment:

  1. thank you pertaining to expressing. i became seeking something like that.


Thanks for visiting!

Note: only a member of this blog may post a comment.