The Journey of Man: A Genetic Odyssey (27 page)
Of course, this scenario is purely speculative, but it may be a plausible alternative to Renfrew’s Indo-European farmers and Cavalli-Sforza’s pre-PIE farmers. Furthermore, the genetic data shows some correlations: most of the regions mentioned, from the Mediterranean
to the Caucasus to Pakistan, have substantial frequencies of M172, our canonical Neolithic marker. This is particularly true for populations from the Caucasus, some of which have frequencies of M172 in excess of 90 per cent. The generally close genetic similarly between Caucasian populations and those from the Middle East suggests that there was a substantial influx of people during the Neolithic, who may have introduced languages related to Sumerian to the region. Of course, this scenario assumes a relationship among all of the Mediterranean languages, which is tenuous at best. However, some linguists have found evidence for such a language ‘superfamily’, revealing deep structures common to seemingly unrelated languages. The search for these superfamilies is where we are headed next.
Charles Darwin, writing in the time before modern methods of language classification had been fully worked out, noted the similarity between classifications based on genealogy and those based on linguistics. In the
Origin of Species
, he noted that ‘if we possessed a perfect pedigree of mankind, a genealogical arrangement of the races of man would afford the best classification of the various languages now spoken throughout the world’. Cavalli-Sforza has said that he was unaware of Darwin’s hypothesis when he began his 1988 comparison between genetic and linguistic relationships, his attention having been drawn to it later by a colleague who studied the history of science. It is not, perhaps, such a great leap of faith to suggest that languages tend to track population relationships. After all, we do ‘inherit’ our language from our parents, so at least on the time scale of the recent past, languages should be a good proxy for genes. What happens, though, when we look further? Is there a deeper relationship among languages that unites them into larger groups? And, perhaps most importantly, is there any evidence of a linguistic equivalent of our genetic Adam or Eve?
Joseph Greenberg, whom we encountered in
Chapter 7
, was convinced that such deeper relationships did exist. He made his name in the field of linguistic classification by uniting the hundreds
of languages of Africa into four distinct families, described in his 1963 book
The Languages of Africa.
These early attempts at higher-order classification were generally well received by the linguistics community, and their success encouraged Greenberg to begin to look tentatively at deeper relationships among languages, particularly those of Eurasia.
Greenberg found that many of the languages, including those belonging to the Indo-European family, seemed to share certain structural elements that they found too striking to be due to chance. The details seem trivial to non-specialists (one example is how nouns are made into plural forms, by the addition of either a -
k
or -
t
suffix), but are significant to many linguists. Merritt Ruhlen, in his book
The Origin of Language
, traces many of the similarities among Greenberg’s so-called Eurasiatic family, called Nostratic by some specialists.
One of the first questions we might have about this group of languages is whether, like Indo-European, there is any archaeological or genetic evidence for it. Unfortunately, this does not appear to be the case. One problem is that its members are so widespread across much of Eurasia that it encompasses a huge number of distinct populations. This may be due to the estimated age of the family – perhaps more than 20,000 years old. Any correlation with such an ancient and widespread group of languages is tenuous at best, and the only obvious Y-chromosome marker would be M9. M9, however, is also found in the other Eurasian superfamily of languages, known as Dene-Caucasian.
The first group in this family is that of the American Na-Dene languages (such as Navajo) and Sino-Tibetan, the languages of China and Tibet. Many linguists now accept the relationship between these two language families, but the more distant relationships are much more controversial. This is because Dene-Caucasian also includes, as its name suggests, languages from the Caucasus, as well as Basque and Burushaski. To put this into perspective, the languages belonging to Dene-Caucasian are spoken from the Pyrenees to the Rockies, with isolated patches scattered across Eurasia – a rather disparate group to say the least. In part because of this, American linguist John Bengtson has identified a subgroup within Dene-Caucasian that includes Basque, Caucasian, Burushaski and the extinct Sumerian
language. The overlap with our hypothetical ‘Mediterranean’ family is striking, and (as we have already seen) there is some genetic evidence to support the dispersal of this group of languages during the past 10,000 years, perhaps in association with agriculture. The inclusion of Sumerian is especially telling, since this language – spoken by one of the earliest Mesopotamian civilizations – has geographic and cultural links back to the earliest days of agriculture in the Fertile Crescent.
While the genetic data supports the notion of a population connection among some of the western members of the Dene-Caucasian family, there is no clear link between them and the eastern languages. These languages, the Sino-Tibetan and Na-Dene families, do have their own genetic connection, however. It comes in the form of the M130 marker, which we first encountered in tracing the coastal migration to Australia. As we saw in the last chapter, M130 is also found in the population of eastern Asia, including China, marking a northward expansion of the marker from south-east Asia. Interestingly, this marker is also found in Na-Dene-speaking populations in North America. As with the Na-Dene languages themselves, it is not found in South America. This suggests a unique genetic link between east Asians and some Native American tribes, which arose from a second migration into the Americas between 5,000 and 10,000 years ago. In this case, genetics reinforces the linguistic relationship and provides a rough date for the divergence.
Their success in identifying common features in languages separated by tens of thousands of years has led some linguists to delve even further into the recesses of linguistic history, searching for the deepest relationship of all – a common origin for all languages. Merritt Ruhlen, one of the staunchest supporters of this view, believes that the Dene-Caucasian family marks the earliest spread of modern humans out of Africa, while the Eurasiatic family marks a later expansion emanating from the Middle East. As we have seen, there is no clear genetic data to support this model. One alternative is that these families spread, at least in part, via cultural dissemination, without leaving well-defined genetic trails. This has happened with some branches of Indo-European, for instance. The other possibility is that Eurasiatic and Dene-Caucasian do not really exist – perhaps they are simply collections of unrelated languages that show random similarities. Or perhaps
subgroups do exist, particularly those supported by genetic data (such as Sino-Tibetan and Na-Dene), while many of the languages are unrelated. Ruhlen clearly has his work cut out for him.
It is likely that the evolution of language does follow the same paths as the migration of modern humans, with an origin in Africa and subsequent dispersal to the far corners of the globe. However, this statement is based on circumstantial evidence – the universality of language in all human populations, extrapolation from short-term linguistic change in recognized families such as Indo-European, and the presumed importance of language for the development of modern human culture. Almost all of the signals of the original human language – if it existed – have been lost, leaving us with today’s dispersed Tower of Babel. In the same way that English fragmented into a large number of dialects that became more dissimilar over the past 500 years, so too do all languages become more dissimilar over time. Eventually, they lose all evidence of their common origin. The period of time required for this is unclear. Some linguists think that 6,000 years is long enough, while Ruhlen and others claim to have found similarities that trace back more than 20,000 years. The search for the language of Adam and Eve promises to be a contentious and exciting field in the next few years, and genetics should be able to offer some input.
The spread of languages is a special case of cultural diffusion, or change. Unfortunately, the attempt to identify cultural change with the migration of people is now seen as old-fashioned in many archaeological circles. Instead, modern archaeologists stress indigenous reasons for the development of cultural attributes, or their borrowing from other cultures. The old school of diffusionism, which attempted to trace the expansion of particular cultures from a single place of origin, has fallen out of favour. However, the genetic results show that in some cases, this has clearly occurred. If genetic and cultural patterns overlap, as in the case of the eastern Dene-Caucasian languages, it is likely that there has been an ancient expansion of people carrying their culture with them. However, it is quite possible to expand a culture
without a concomitant movement of people. This may have happened with the expansion of farming into north-western Europe.
As geneticists, we are limited by what we study. While we take history, archaeology and languages into account in our interpretations; our unique contribution is our ability to trace genealogy – actual biological relationships. Thus, we can find evidence to support human migration, as in the case of M17 and the steppe culture, as well as to refute it. Language is a good cultural attribute to study, since there are often written records. Even when there aren’t, the relationships among languages can be examined systematically. Most cultural processes are not like this, making their interpretation more problematic.
One concept of race, popular until the mid-twentieth century, was that the different skin colours of people around the world reflected deep-seated biological differences. This was Carleton Coon’s argument, and he used it (as well as skull shape and a few other characteristics) to divide humans into discrete population units. Earlier classifications had used cultural attributes as part of their racial definitions, as anthropologist Jonathon Marks has pointed out. Linnaeus, for example, had included ‘obstinate, contented, free; paints himself with red lines’ in his description of the American subspecies of
Homo sapiens.
Clearly, there was no biological basis to this – otherwise every Native American alive today would feel genetically compelled to paint his or her face. This archaic confounding of race and culture has had terrible consequences, most obviously during the heyday of eugenics. But, as we saw with the spread of languages, there are sometimes correlations between culture and genetics. Old-fashioned eugenicists may have taken this as evidence of a genetic
cause
for the cultural attribute, but in fact – as recent research shows – it is probably quite the opposite.
The Karen people of northern Thailand and Burma are perhaps not as well known as their neighbours the Padaung, with their neck-extending rings of brass, but they are fascinating to ethnographers. This is because their social system runs counter to the pattern common in the vast
majority of the world. Over 70 per cent of the world’s societies practise something known as patrilocality. In this type of society, men control the wealth. Inheritance – and group membership – is passed through the male line. When two people marry, the wife goes to live with her husband and assumes a new identity in her husband’s clan. The European custom of a wife changing her name to that of her husband traces its origin to this type of patrilocal behaviour.
One of the effects of patrilocal behaviour is that men tend to stay in one place while women are constantly immigrating into the family or clan. This may seem counter-intuitive – after all, don’t men sow their wild oats more than women? – but it is the rule in most societies. The Karen, in contrast, do things differently. In Karen society, everything is turned upside-down. Women control the wealth, and group identity is passed through them to their daughters. In Karen marriages, men immigrate to the woman’s village, taking over the care of her fields. Their society is what anthropologists term matrilocal, in that the women stay put and the men move. While the Karen may seem like ethnographic curiosities, in fact they have been instrumental in revealing the effect of culture on human genetic diversity. Like a bespoke experiment, they provide a social contrast to the prevailing pattern in human populations around the world.
We have used the Y-chromosome for most of our studies of human migration. This is because the Y shows greater differences in frequency between populations than most other genetic markers. As Dick Lewontin’s analysis showed, most of the genetic diversity in the human species is found within populations, with a tiny fraction – 10 to 15 per cent – distinguishing between. For the Y, 30 to 40 per cent of the diversity is found between populations. Greater genetic contrast provides better resolution, which is why the Y is so good at tracing migrations.
When the Y was first studied as a marker of population affinity, one of the results that kept popping up again and again is that it connected people to a particular location. With a few DNA polymorphisms, it was possible to achieve incredible geographic resolution – there were even Y-chromosome polymorphisms that were limited to particular villages. If you imagine population genetics as a game of twenty questions, most genetic systems, including blood groups and mitochondrial DNA, needed all twenty to identify even the coarsest pattern,
such as which continent the individual came from. In contrast, the Y could typically identify subcontinental regions with a few questions. The observation, then, was that Y-chromosome lineages were geographically localized – they tended to define people as coming from a particular place. A fantastic tool for studying population movements, but the explanation for the pattern remained elusive.
