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Archiver > GENEALOGY-DNA > 2007-03 > 1172849914


From: "Lawrence Mayka" <>
Subject: Re: [DNA] Lactose tolerance evolved recently
Date: Fri, 2 Mar 2007 09:38:34 -0600
In-Reply-To: <4ebd44335ajohn@cartmell.demon.co.uk>


> [mailto:] On Behalf Of John Cartmell
> They may have just spread the culture. The genome may well
> have been in the receiving population all along and the
> culture simply selected the appropriate individuals.

That was the old assumption, mentioned by AlanR in a December 2006 post.
But the new reseach we are discussing does not support that.

1) The lactase persistence allele was _not_ present in Neolithic communities
across Europe dated to the 6th millennium B.C.:

http://www.sciencedaily.com/releases/2007/02/070227105530.htm
---
The team carried out DNA tests on Neolithic skeletons from some of the
earliest organised farming communities in Europe. Their aim was to find out
whether these early Europeans from various sites in central, northeast and
southeast Europe, carried a version of the lactase gene that controls our
ability to produce the essential enzyme lactase into adulthood. The team
found that it was absent from their ancient bone DNA.
---

2) A single, recently arisen lactase persistence allele is responsible for
all milk-drinking ability in northern Europe:

http://www.geneticarchaeology.com/Research/Lactose_tolerance_gene_proves_Nat
ural_Selection_in_humans.asp
---
Region | % of Population Lactose Tolerant | Age of Gene
| Age of Domestication of Cattle
West Africa | 5 to 20% | 6000 to
7000 years ago | 7700 to 9000 years ago
Africa | 26 to 88 % | 2700 to
6800 years ago | 3300 to 4500 years ago
Southern Europe | 50% | 8000 to 9000
years ago | 8000 Years Ago
Northern Europe | 90% | 2000 to
20000 years ago | 8000 Years Ago
..

Her study, shows that the lactase persistence gene that has evolved in
Africa has evolved independently of the gene variants predominant in Europe.
So far she has identified 6 different variants of the gene.
---

I am unfortunately unable to afford the original report, whose abstract is
here:

http://www.nature.com/ng/journal/v39/n1/abs/ng1946.html

However, the summary above seems to give us some new information:

A) No one has yet studied lactase persistence in northern and central Asia,
so we don't know whether the people of Kazakhstan and Mongolia share the
northern European allele for lactase persistence, or whether they have their
own. This issue might be crucial to understanding the anthropologically
recent expansion of R1a eastward as far as Mongolia, and the expansion of
Indo-European southward into India.

B) The table strongly implies that southern Europe has its own lactase
persistence allele, but the relatively low 50% rate of occurrence suggests
that the natural selection effect was much weaker there. Based on other
recent research I cited in an earlier post, the simplest explanation is that
milk-drinking affords an enormous advantage to nomadic peoples who must
travel across steppes, savannas, or deserts. Milk-drinking is useful but
not absolutely decisive in settled agricultural societies, who have other
sources of fluid and nutrition and who have the time to produce cheese if
they wish. Hence, the highly settled, agricultural southern Europeans never
evolved milk-drinking ability as pervasively as populations in other regions
where nomadic lifestyles were (and in some cases still are) common.


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