Chapter 9 What Molecules Can't Tell Us About the Spread of Languages

What Molecules Can’t Tell Us Chapter 9 What Molecules Can’t Tell Us about the Spread of Languages and the Neolithic Hans-Jürgen Bandelt, Vincent Macaulay & Martin Richards A wealth of molecular sequence data seems to have hapless hunter-gatherers as it flooded in. Curiously revolutionized our knowledge about the distant past, though, for us (being familiar with our Dennell, so what can molecular geneticists tell us about the Barker and Whittle), the initial interest lay in the spread of languages and the Neolithic? How does discovery that there were some Neolithic immigrants inference proceed — from data to tales? Is the ge- after all. It even seemed that an estimate of ~20 per netic approach the key to a new synthesis? We will cent Near Eastern Neolithic ancestry in Europe might retell some stories of past and recent publications, actually be taken as rather strongly confirming (at briefly comment on them and discuss the potential least one interpretation of) the Cavalli-Sforza et al. of the future and the limits of the genetic programme. picture, viz. the colonization model of farming ori- gins. The ‘archaeogenetic’ enterprise It soon became clear, though, that there might be more mileage in taking on the demic-diffusionists Following Amorim (1999), and echoing the ‘geneti- rather than the indigenists, especially as it seemed cal archaeology’ of von Haeseler et al. (1996), Ren- that a certain dogmatism had set in amongst the frew (2000) coined the term ‘archaeogenetics’ for ‘the former camp. But it was not clear that such a low newly-emerged discipline which applies molecular Neolithic input was incompatible with demic diffu- genetics to the study of the human past’. His earlier sion, or even a ‘wave of advance’. So it was not suggestion of ‘historical genetics’ (Renfrew 1992) simply ‘new data’ that moved this debate forward, never really gained currency amongst geneticists, but a consideration of those data in the context of, despite the elegant evocation of historical linguis- for example, arguments such as those of Zvelebil tics. To be awkward, we will adopt the latter expres- (1986) concerning the archaeological context, and a sion, which we have only just discovered; this can consideration of how seriously the more rigid inter- serve to remind us of the delay in communications pretations of the classical marker gradients needed that often hinders relations between archaeologists to be taken. Indeed, in 1996 the evidence for which and geneticists. mtDNAs arrived when was rather weak, because of It was in the late eighties that molecules such as the paucity of Near Eastern data. A minor subhaplo- mtDNA began to tell stories, with the ‘Out-of-Af- group (T1) was subsequently shunted into the rica’ narrative (Cann et al. 1987). This wave of ad- Neolithic component (Richards et al. 1998), and the vance soon reached Europe: Richards et al. (1996), distinction between ‘Palaeolithic’ and ‘Neolithic’ lin- putting molecules rather than populations into an eages eventually became somewhat fuzzier, as more archaeological context, saw the Neolithic arriving Near Eastern data were considered (Richards et al. with members of one major mitochondrial 2000), moving us away from a rather simplistic ‘one haplogroup (J). The context of discovery for most haplogroup–one migration’ model. geneticists at the time was, of course, the demic- In any case, more than three quarters of the diffusion model of Cavalli-Sforza and his colleagues mtDNA remain firmly rooted in the European (Menozzi et al. 1978). This had gradually been inter- Palaeolithic. But there is clearly some flexibility in preted as a tidal wave of farmers swelling into Eu- the way in which stories about such data can be told. rope from the Near East, engulfing small bands of Can we be sure that the ancestors of the ‘Neolithic’ 99 Chapter 9 mtDNAs were carried into Europe along with the Since the methodology of this classic series of very first cereals and goats? Hardly, although ex- papers on Saami/Finnish mtDNA still lives on, one actly this inference was the fallback position at the needs to take a closer look at how data were turned time, when the predominant view among geneticists into tales in this case. The HVS-I data were proc- was that of Neolithic replacement or waves of ad- essed by Sajantila et al. (1996) in a quite peculiar vance, so that any molecules which could be tied to way, discarding most of the polymorphic sites as the spread of the Neolithic were greeted with enthu- recently mutated. The ‘rationale’ for this was an er- siasm. A molecule entering in the Early Neolithic roneously-presumed statistical sorting, in that slow could well have had a Mesolithic carrier — it de- sites preferably changed in the distant past while pends on the archaeological reconstruction whether fast sites did so relatively recently. For the distinc- Neolithic or Mesolithic affiliation is more likely. Once tion of slow vs fast, they appealed to Hasegawa et al. the Neolithic became established, exchange networks (1993), who reconstructed multiple hits at the HVS-I broadened, allowing for introgression of molecules sites for the worldwide mtDNA data set available at during subsequent stages. Perhaps a number of mi- the time. Sajantila et al. (1996) regarded those sites tochondria rolled along with the secondary-prod- listed with exactly one hit as the potentially most ucts revolution (Sherratt 1981)? conservative sites — thus ignoring the most con- Molecular genetics, however, is conventionally servative candidates, viz. the sites unvaried (i.e. zero seen to fuel a ‘new synthesis’ centred on ‘population hits) in the test data of Hasegawa et al. (1993). Het- history’ (Renfrew 1999b). A prime example of a (far erozygosity values calculated with respect to those from grand) synthesis attempted by human geneti- ‘one-hit’ sites then were apparently much smaller cists in this spirit is laid out next. for the Finnish sample compared to the samples from most other European sources. This effect, however, The Finnish Adam and Eve story completely disappears when the zero-hit sites are also taken into consideration. Why are Finns so alike physically? A commentary in Now comes the dating of the perceived mito- th journal ‘Science’ (Holden 1996) revealed the excit- chondrial bottleneck that should account for the low- ing reasons uncovered by molecular geneticists: the seeming diversity of the Finnish mtDNA pool. The Finns descended from a small band of people who average nucleotide difference in the 360-bp segment settled in what is now Finland some 4000 years ago of HVS-I was calculated as 3.9 substitutions (all sites (Sajantila et al. 1996). Their language was originally having been put back for this exercise). One unit of Indo-European but later these people switched to pairwise difference scaled with the divergence rate Finnish, which they learnt from their Saami neigh- of Ward et al. (1991) would then correspond to 8,300 bours (Sajantila & Pääbo 1995). The Saami, on the years, but Sajantila et al. (1995, 1996) enigmatically other hand, appear to have been separated from the cited this as 13,000 years. On top of this, they con- other European populations for tens of thousands of founded divergence rate (the rate at which two line- years (Sajantila et al. 1995). The data on which these ages diverge from a common ancestor) with sweeping claims were based were a meagre handful substitution rate (the rate at which a lineage diverges of Y-chromosome microsatellites and the mitochon- from an ancestor), so that they effectively turned the drial hypervariable segment I (HVS-I). false 13,000 years into 6500 years (a lab-specific blun- None of those assertions has had a long half- der; see Bandelt & Forster 1997). Even then the per- life as more data from Finland accumulated; cf. Kittles ceived bottleneck came out too old for the story to be et al. (1999), Peltonen et al. (2000, Box 2), and Finnilä told. So, a substitution rate faster by more than an et al. (2001). As to the question of potential language order of magnitude was invoked (gleaned from ma- replacement in Scandinavia, most scholars prefer to ternal pedigree studies; cf. Pääbo 1996): this gave an believe that Proto-Finnic, ancestral to the present- age reported as 3900 years, which again has to be day languages Saami, Finnish, Estonian etc., spread halved (now, however, turning out to be too young) into the eastern Baltic area during the Eastern Bronze because of the substitution/divergence confusion. Age, thus eventually leading to a complete replace- The slightly earlier published story about the ment of the languages spoken earlier in the area of Saami (Sajantila et al. 1995) uses the conventional Finland. In particular, Kallio (2000) suggests (in modi- mutation rate and genetic distances in the form of fying Posti’s theory) that the Proto-Baltic and Proto- net nucleotide differences, which are the averaged Germanic speakers in the area became Finnic nucleotide differences between two populations mi- speakers (Finnic notabene, not Finnish). nus the average of the averaged nucleotide differ- 100 What Molecules Can’t Tell Us ences within the respective two populations. Al- theoretically convenient (it means that each gene though no attempt was made to scale these genetic copy throughout the history of the sample is a part distances to absolute time (using the assumed muta- of a population of the same size), it could not be said tion rate), Sajantila et al. (1995) tacitly assumed that to be useful. Even under (marginally) more realistic the ages of typical population splits in Europe were scenarios of different population sizes in the three of the order of a few thousand years, so that the populations, linearity in the time of the split is lost, genetic distances of the Saami to the other European unless the daughter populations have been going populations would correspond to tens of thousands their separate ways for a very long time.

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