Lactase/lactose tolerance

slowburner

This might seem to be an obscure sort of subject to post here but it is potentially one of the most significant factors which allowed man to become established in the chillier, darker climes of northern Europe.
It seems that we northern Europeans produce the enzyme lactase which confers the advantage of being able to digest lactose.

Research tracing the distribution of the genetic marker for lactase persistence might even map the spread of neolithic dairy farming.

Author Summary

Most adults worldwide do not produce the enzyme lactase and so are unable to digest the milk sugar lactose. However, most people in Europe and many from other populations continue to produce lactase throughout their life (lactase persistence). In Europe, a single genetic variant, −13,910*T, is strongly associated with lactase persistence and appears to have been favoured by natural selection in the last 10,000 years. Since adult consumption of fresh milk was only possible after the domestication of animals, it is likely that lactase persistence coevolved with the cultural practice of dairying, although it is not known when lactase persistence first arose in Europe or what factors drove its rapid spread. To address these questions, we have developed a simulation model of the spread of lactase persistence, dairying, and farmers in Europe, and have integrated genetic and archaeological data using newly developed statistical approaches. We infer that lactase persistence/dairying coevolution began around 7,500 years ago between the central Balkans and central Europe, probably among people of the Linearbandkeramik culture. We also find that lactase persistence was not more favoured in northern latitudes through an increased requirement for dietary vitamin D. Our results illustrate the possibility of integrating genetic and archaeological data to address important questions on human evolution.

http://www.ploscompbiol.org/article/info%3Adoi%2F10.1371%2Fjournal.pcbi.1000491

JuliusCaesar

Raymond Crotty the economist proposed this theory way back in the 1970s before any biological work had been done. It's in his posthumous book, When Histories Collide, but I think he may have published it before...certainly I remember people talking about it then. From here:

He authored books on the Irish economy and politics and on cattle farming. He had largely finished the manuscript of this much more ambitious book in 1992, but he died in 1994 before it was ready for publication. His son struggled through rejections of the manuscript but eventually found a publisher with the aid of Norwegian sociologist Lars Mjøset, who immediately recognized its quality and wrote the book's fine introduction.

slowburner

What a fascinating thinker, certainly ahead of his time.
His political campaign of 1986 is more than pertinent today.

The earliest reference I could find to any other thinking on lactose tolerance, was 2004.

Considering the theory of a genetic linkage between Irish and Basque populations, this might be of interest.

dubhthach

There's a new report based on ancient-DNA from Iberia that was recently published. It shows "Lactase persistence" in Neolithic remains which kinda puts a blunt on the idea that the trait came into Europe via migration of pastoralists in the post-Neolithic era (Bronze age for example)

http://dienekes.blogspot.com/2012/01/lactase-persistence-in-neolithic-iberia.html

Low prevalence of lactase persistence in Neolithic South-West Europe
European Journal of Human Genetics advance online publication 11 January 2012; doi: 10.1038/ejhg.2011.254

he ability of humans to digest the milk component lactose after weaning requires persistent production of the lactose-converting enzyme lactase. Genetic variation in the promoter of the lactase gene (LCT) is known to be associated with lactase production and is therefore a genetic determinant for either lactase deficiency or lactase persistence during adulthood. Large differences in this genetic trait exist between populations in Africa and the Middle-East on the one hand, and European populations on the other; this is thought to be due to evolutionary pressures exerted by consumption of dairy products in Neolithic populations in Europe. In this study, we have investigated lactase persistence of 26 out of 46 individuals from Late Neolithic through analysis of ancient South-West European DNA samples, obtained from two burials in the Basque Country originating from 5000 to 4500 YBP. This investigation revealed that these populations had an average frequency of lactase persistence of 27%, much lower than in the modern Basque population, which is compatible with the concept that Neolithic and post-Neolithic evolutionary pressures by cattle domestication and consumption of dairy products led to high lactase persistence in Southern European populations. Given the heterogeneity in the frequency of the lactase persistence allele in ancient Europe, we suggest that in Southern Europe the selective advantage of lactose assimilation in adulthood most likely took place from standing population variation, after cattle domestication, at a post-Neolithic time when fresh milk consumption was already fully adopted as a consequence of a cultural influence.

The Late Neolithic remains that aDNA was extracted from are from 4500-5000 years old