No Saxon invasion?

[authun]

Therefore Halsall is correct, the authors have "suggested that DNA can ‘prove’ that there was mass migration and dramatic population change in lowland Britain in the fifth and sixth centuries". In most sciences the 'best explanation' is 'proof'.

Peer science builds on the findings of previous studies, testing the validity of some of their assumptions as a control, creating new models, seeing how the new data fits within those models and making proposals for further research. So, it's not final proof. It's a step forward in the sum total of knowledge. To quote Mike Weale's presentation on this, "The observed data from the sample set is best explained by a single mass migration event that occured between 50 and 60 generations ago if the assumptions used in our models are correct". As he states in the study, "We note, however, that our
data do not allow us to distinguish an event that simply added to the indigenous Central English male gene pool from one where indigenous males were displaced elsewhere or one where indigenous males were reduced in number." There is no claim that the findings explain the observed data in unequivocal terms.

One has to look at the assumptions used. These are things like the correct identification of the indigenous and source populations, the population growth rates, the microsatellite mutation rates and so on. For example, from the paper, "Furthermore, although our models assume a single instantaneous migration event, we would also expect a more gradual process lasting several generations but still resulting in the same degree of admixture (a picture which may fit the historical data better [Härke 2002]) to produce very similar genetic patterns."

Identification of the indigenous population was based on Jim Wilson's 'Genetic evidence for different male and female roles during cultural transitions in the British Isles', which used North Wales as the base for the indigenous population of England. Weale warns however "However, the study of Wilson et al. did not directly address the effects of cultural transitions in other areas of Britain." So one assumption is that England, prior to the influx of the new genetic lineages should look like North Wales. In fact Weale's sample centres, Llangefni and Abergele do not show the homogenity Wilson suggested. Abergele is in a completely different part of the PC plot (fig. 3) due to the high frequency of Hg21. Studies to explain this feature are ongoing and it may be the result of copper miners from the Balkans during the Bronze Age.

All the models used assume exponential growth rates with various plausible values (personal correspondence). Moreover, equal growth rates are assumed for the indigenous and newly arrived populations. There is no reason to assume the latter and the former is not correct. One only has to think of the plagues in the middle ages to see that the population has crashed at certain times rather than grown exponentially. If and how changes to the models' assumptions would affect a change in the outcome is hard to tell without creating a more accurate population model, but that is outside the scope of this particular study because it never set out to prove anything. It simply offers a best explanation within the constraints of the models and assumptions used.

The timings for the influx of the new paternal lineages are based on the microsatellite mutation rates. Again, assumptions are made about these; "Finally, we accept that our inferences are based on population genetic analyses that assume a particular model of microsatellite evolution under selective neutrality and growth and that departures from these assumptions may influence our results." and Weale devotes a good deal space to explaining the importance and use of microsatelite data.

Weale is very clear about what the observed data is, how the models functioned and what the assumptions were. He didn't offer it as final proof.

Again Halsall is correct. How do the authors know this is not of the effect of several migrations (in Neolithic or later)? They don't, they just assume it's one big migration

No they don't. They test three models which are explained in the text along with the values for the factors.

(1) Island model (TS 5),
(2) Neolithic (TS 5 240 generations BP or 6,000 years BP assuming 25 years per generation)
(3) Anglo - Saxon (TS 5 60 generations BP or 1,500 years BP assuming 25 years per generation).

Halsall does not challenge it on technical grounds. Who's not reading whom?

I didn't say Halsall challenged it on technical grounds. It has never been challenged on technical grounds. It has only been criticised by people without technical expertise.

There's no bias.

OK you disagree but to me, including personal opinion like "quite apart from the fact that it seems to me to be principally aimed at getting the researcher in question into the headlines" suggests an unnecessary emotional content which betrays an underlying motivation.

Halsall continues (why the '...' ?) with "is that it is framed around questions aimed at a view of post-imperial history from over a century ago." And that is a problem indeed. For Weale et al an Anglo-Saxon is biologically so and that's so 19th-centurish!

All these guys who are trained in ethnicity do so from an ethnographic viewpoint. The ethnogenesis of any group is considered in terms of composition, settlement, material and spiritual cultures and so on. The biology is seen as largely irrelevant. So, you see for example statements such as 'the history of the Goths starts in 238 AD'. The question, 'what were they doing in 230 AD and where were they?' is unanswered but, in the wider field of settlement history, it is the question most of us want an answer to.

As for the "great number of studies", apparently there are few genetic studies about Anglo-Saxon invasion (you mentioned two). If Weale et al hadn't addressed the Anglo-Saxon (or some other major) migration, arguably their study would have enjoyed less popularity.

As you say, Weale and Capelli's study were popular but that is different from what the author claimed. He claimed that gaining popularity was the intention behind the study. He uses the term 'principally aimed'.

It's complete rubbish. If publicity was the motivation, they wouldn't be publishing in Molecular Biology and Evolution. It's hardly a best seller at WH Smiths.

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