Sadly, Camper’s iconography spoke louder than his words, and his diagram with its implicit demonstration of a hierarchy from ape to Apollo (with Africans rather closer to apes than to gods) became a staple of nineteenth-century anthropology. There is no need to recap and critique the craniometric studies carried out in the nineteenth and early twentieth centuries that sought to demonstrate that one subset of humanity was more or less intelligent than another – others have done so with a thoroughness that their scientific influence scarcely merits. But it is worth noting that modern physical anthropologists remain keen on describing skull shape, though nowadays they tend to do so with 3-d laser scanners and multivariate statistics. They find, perhaps unsurprisingly, that for all the variety within populations, people from different parts of the world have different-shaped heads.
Much as Camper claimed, the jaws of sub-Saharan Africans do protrude, on average, further from their foreheads than do the jaws of Europeans – an attribute known as ‘prognathism’. Melanesians and Australian Aborigines are also more prognathic than Europeans. Contra Camper, however, this does not make African (or Aborigine) skulls more like ape skulls than European ones. The facial angle is a rather crude way of capturing an exceedingly complex aspect of skull shape. It does not discriminate between different ways of being prognathic. A chimpanzee has a high facial angle because its whole face and forehead slope; Africans and Aborigines have slightly higher facial angles than Europeans because of a jut in the jaw alone. Besides, Europeans do not even have the flattest faces. That honour – if honour it is – must go to the Inuit of northern Canada.
Human skulls are wonderfully diverse. The Inuit are also notable for the largeness of their eye orbits and the massiveness of their cheekbones. Compared to everyone else, the Khoisans of southern Africa have bulging foreheads (frontal bossing); Australian Aborigines have massive brows (supra-orbital ridges); some sub-Saharan Africans have widely set eyes (large inter-orbital distances); Andaman Islanders (negritos) have small, round skulls – the list of differences could be extended indefinitely. Few of these differences are absolute. Just as most of the variance in gene frequency is found within, rather than among, populations (nations, continents), so too is most of the variance in skull shape. And the differences among populations are all subtle. Australian Aborigines and Inuit differ in prognathism by only 6 per cent. Small differences, then, but differences that, given the attention we devote to each other’s faces, strike us immediately.
My claim that we will soon be able to identify the genes responsible for all this diversity in skull shape suggests an important question: namely, do such genes exist? In 1912 the American anthropologist Franz Boas set out to demonstrate that they do not. A humane and tolerant man, he was an implacable opponent of those who sought to make invidious distinctions between humanity based on the shapes of their skulls. The following passage, taken from a serious anthropological article written in 1905 by a German dentist called Rose, gives a flavour of what he was up against: ‘The long heads of German descent represent the bearers of higher spiritual life, the occupants of dominant positions, to which they are destined by nature, the innate defenders of the fatherland and the social order. Their whole character predetermines them to aristocracy.’ And so on, to the detriment of the more democratically minded and un-German ‘round heads’.
The ‘long’ and ‘round’ heads refer to the value of the ‘cephalic index’, the ratio of skull breadth to width (expressed as a percentage, long heads or dolichocephalics have a cephalic index below seventy-five, while round heads or brachycephalics have a cephalic index above eighty; mesocephalics are somewhere in between). Noting that the immigrants who arrived at Ellis Island – Bohemians, Slovakians, Hungarians, Italians, Scots and Eastern European Jews – varied somewhat in their cephalic indexes, Boas asked whether these differences were due to genetic (to use his terminology, ‘racial’) or environmental causes. He reasoned, soundly, that if the skulls of the American-born children of all these various groups were more similar to each other than those of European-born children, then environment rather than ancestry must be the cause of the differences. Boas measured some thirteen thousand heads – a vast undertaking that left him, in the absence of computers, overwhelmed by numbers. Nevertheless, he managed to produce a graph that seemed to show that the cephalic indices of the US-born children of Sicilians and Eastern European Jews (both rather dolichocephalic to begin with) were, indeed, converging. It was a case of new heads for the New World.
Boas’s study dealt a near-fatal blow to craniometry. Over the last ninety years it has been cited innumerable times – not least by the late Stephen Jay Gould – as proof that skull shape is ‘plastic’, that is, caused by non-genetic differences. Boas, however, was wrong. His data have recently been comprehensively re-analysed using modern statistical techniques. The skulls of American-born children do indeed differ from those of their parents, but they do so inconsistently. Indeed, had Boas chosen to compare the children of Scots and Hungarians, rather than those of Sicilians and Eastern European Jews, he could have shown that America causes skulls to diverge rather than converge in shape. But he was wrong in a deeper sense than this. Re-analysis of his data also shows that the changes in skull shape caused by American birth, whatever their direction, are trivial compared to the differences that remain and that are due to ancestry and family – or, to put it more succinctly, to genes. Indeed, looking beyond European immigrants, this is hardly surprising. Forensic anthropologists in the United States and Britain are quite adept at telling whether a given skull, perhaps evidence of some foul deed, once belonged to someone of African or European ancestry. That they can do so after decades, even centuries, of co-existence, not to mention generous amounts of admixture, suggests that our differences are not, as is often said, merely skin deep, but extend to our skulls – if not to what they contain.
So, genetic differences exist among all sorts of people. Should we try to find out what they are? Many scientists think not. Some find it enough to dismiss such physical diversity as exists among human populations as ‘uninteresting’ – not worthy of study. Others concede that it may be interesting, but that it should not be studied, since even to contemplate doing so is to engender social injustice. They fear a revival of not merely racial, but racist, science.
For my part, I should love to know the genes responsible for human diversity; the genes for the differences – be those differences between men and women who live in the same village or those who have never trodden on each other’s continents. In part this is simply for the pleasure of knowing. This the pleasure that comes from looking at Gabriel Dante Rossetti’s painting La Ghirlandata and knowing that his model, Alexa Wilding, had two loss-of-function MC1R mutations that gave her such glorious red hair. This pleasure of knowing is partly that which all science gives, but to which is added the pleasure that comes from understanding the reason for something that has been hitherto at once familiar but completely mysterious.