Ancient "Swedes" were "lactose intolerant"

By Razib Khan | April 1, 2010 6:26 am

ResearchBlogging.orgMy recent focus on the lack of genetic continuity between hunter-gatherer and farming populations genetically and culturally is primarily due to the fact that we’re not in theory-land; the extraction of ancient DNA samples is steady-as-it-goes and is sharpening and overturning our understanding of the past. The relationship between culture and genetics is of particular importance in this case, genes serve not only as markers which we can track population movements, but genes themselves are embedded in dynamics which need not be connected to population movements.

Consider lactase persistence, which confers the ability to digest milk as an adult. In the 20th century “lactose intolerance” was assumed to be a pathology, but it turns out that most human populations can not digest milk sugar as adults due to the lack of production of the lactase enzyme. This is the ancestral type. Rather, different mutations which result in the persistence of lactase production into adulthood seem to have arisen independently in several regions of western Eurasia and Africa. This suggests that the mutational target zone here is large, that is, given particular selection pressures (cattle culture) mutants will arise in the background and increase in frequency which produce the phenotype of lactase persistence.

The region of the world where lactase persistence is at highest frequency and greatest extent is northern Europe. It turns out that the region around LCT, the locus functionally implicated in variance of the trait of lactase persistence, has an enormous region of linkage disequilibrium around it. In other words, recombination hasn’t chopped up correlations of genetic variants along DNA strands. As you know this implies several possible evolutionary events, and may be a telltale signature of natural selection in the recent past.  In much of western Eurasia it seems that one SNP, -13910*T, is responsible for the shift from ancestral to derived state in regards to lactase persistence. In other words, one gene copy which had a mutant from C to T rose rapidly in frequency from northwest Europe to northwest India (there are different alleles among Arabs and various populations in the Sahel).

There has already been suggestive data that ancient European populations lacked the -13910*T variant. A new study seems to confirm this. High frequency of lactose intolerance in a prehistoric hunter-gatherer population in northern Europe:

Results
Here we investigate the frequency of an allele (-13910*T) associated with lactase persistence in a Neolithic Scandinavian population. From the 14 individuals originally examined, 10 yielded reliable results. We find that the T allele frequency was very low (5%) in this Middle Neolithic hunter-gatherer population, and that the frequency is dramatically different from the extant Swedish population (74%).

Conclusions
We conclude that this difference in frequency could not have arisen by genetic drift and is either due to selection or, more likely, replacement of hunter-gatherer populations by sedentary agriculturalists.

The sample size here is small. But they ran some simulations and it seems unlikely that so few hunter-gatherers would have the derived frequency which is extant at high frequencies among modern Swedes. Additionally, we know that this locus shows signatures which might indicate recent natural selection. That is, it rose in frequency recently in many populations. And there are a other studies from Germany which suggest a similar transition, whereby ancient populations lacked lactase persistence.

gotlandmapThe samples were from the island of Gotland, and date from 2,800-2,200 BCE. In other words, contemporaneous with the Sumerian civilization and Old Kingdom Egypt. This might be prehistoric in Europe, but not on a worldwide scale. They were from the Pitted Ware Culture, and predated agriculture in this region by about ~1000 years. Here’s what Wikipedia says about the PWC:

The Pitted Ware culture (ca 3200 BC– ca 2300 BC) was a neolithic Hunter-gatherer culture in southern Scandinavia, mainly along the coasts of Svealand, Götaland, Åland, north-eastern Denmark and southern Norway. It was first contemporary and overlapping with the agricultural Funnelbeaker culture, and later with the agricultural Corded Ware culture.

Some sources seem to suggest that the in the zone of the Funnelbeaker culture which succeeded the PWC  we invariably see contemporary high frequencies of lactase persistence. So these results are not inexplicable or a total shock. The main question is this: did the genetic variant spread to Scandinavia through positive selection, or population movement, or a combination? A reasonable guess would be some of both, but the real answer lay in establishing the proportion. In other words, how many of the hunter-gatherers were assimilated? The high fitness benefits conferred by LCT means that even in an admixed population it would rise in frequency. The main suggestive aspect here is the one individual who is a heterozygote. Phenotypically they should express lactase persistence. Who was this individual? Unfortunately they didn’t get more of the total genome, but this person might have been of mixed origin, and so illustrate the complex dynamics of how farming spread.

A few years ago I would have assumed that LCT spread in Europe by natural selection, introgressing into the hunter-gatherer substrate as they adopted farming and cattle culture. Today I am not sure. It is clear that lactase persistence has been subject to natural selection, but that does not entail that it spread only through individual level dynamics. On other words, population replacement is now a serious possibility. That opens up the likelihood that much of the population of northern Europe are relatively new settlers in the context of human history, that they even post-date the civilizations of Egypt and Mesopotamia. Interesting times.

Helena Malmstrom, Anna Linderholm, Kerstin Liden, Jan Stora, Petra Molnar, Gunilla Holmlund, Mattias Jakobsson, & Anders Gotherstrom (2010). High frequency of lactose intolerance in a prehistoric hunter-gatherer population
in northern Europe BMC Evolutionary Biology : 10.1186/1471-2148-10-89

CATEGORIZED UNDER: Culture, Genetics, Science
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  • Georg

    Hello,
    what about the Sami, that rendeer breeders
    in northern Scandinavia?
    Georg

  • John Emerson

    I’m not sure how solid the consensus is on the Indo European migraption / diffusion is, but per Wiki and per what I remember from various sources, it’s likely that these Swedes are not Indo-European. According to Wiki this area was not Indo-European in 2500 BC and may have been European in 1000 BC. Despite the extreme Nordicness of Scandinavia, Indo-Europeans got there rather late.

    Honest, I have other, better sources, but Wiki is convenient and it fit with what I remember.

  • http://www.evoandproud.blogspot.com Peter Frost

    If northern Europeans are relatively recent to northern Europe, wouldn’t that imply that their physical characteristics are also recent? Unless I’m missing something, all of the phenotypic changes would have to be squeezed into a very short time span, i.e., between the arrival of agriculture (7,500 BP – 3,000 BP)and the earliest historical descriptions of northern Europeans (about 4,000 BP).

  • megan

    Hey, took reading through things at ScienceBlogs to follow Razib Khan here! =P
    RSS should have a newsletter option, then I could always get posts whereever on the net Razib blogs.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    If northern Europeans are relatively recent to northern Europe, wouldn’t that imply that their physical characteristics are also recent?

    not necessarily. i’m focusing on a specific germany-to-scandinavia locale cuz that’s where we have ancient DNA samples right now. so there are many different models.

    but i think the current consensus of data does point to the likelihood that salient northern european characteristics are relatively new, though the date you give might be a touch low. though my confidence on this is also only modest at best…there’s just a lot of uncertainty, and after the most recent overturning of “orthodoxy” i think it is probably best to let things settle out before we get as definitive as we were between 2000-2007 (the sykes & oppenheimer position re: european ancestry that is).

  • Melykin

    If northern European hunter gatherers were replaced by farmers from further south so recently, then wouldn’t Europeans be more genetically homogenous than they are? The Scandinavians tend to be taller and blonder than other Europeans. The Scots have a higher portion of red haired people than any other country. Could these changes have happened in the last 2000 years?

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    If northern European hunter gatherers were replaced by farmers from further south so recently, then wouldn’t Europeans be more genetically homogenous than they are?

    they are very genetically homogeneous compared to southern europeans who are more homogeneous than middle easterners who are more homogeneous than aricans. also, i suspect that many northern europeans are composites of newcomers and old timers, so the homogeneity induced by population bottlenecks as newcomers emigrate is balanced a bit by the diversity extant in the local substrate which is soaked up.

    Could these changes have happened in the last 2000 years?

    what do you mean quantitatively? that they were lower frequency 2000 years ago, or zero? i think allele frequencies may have changed appreciably though, yes. also, the blondest people are i believe lithuanians and other east balts, though it is close (anglospherics are more familiar with people from the west baltic for obvious reasons).

    also, re: a previous commenter, i think the probability exists that the sami are relicts or offshoots of the paleo northern europe population. this population then obviously has had some genetic impact on finns, swedes, norwegians and danes, in that order (look at allele frequencies or what they look like).

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  • Melykin

    what do you mean quantitatively?

    Scandinavia, Scotland and Ireland seem to have higher rates of alcoholism than places farther south in Europe. Since very high rates of alcoholism are seen in hunter gatherer populations (such as aboriginal people in Canada and Australia), I’m wondering if people in northern Europe are more recently descended from hunter gatherers than people in southern Europe. Or are the people now living in northern Europe descended entirely from farming populations that moved there from southern Europe?

    Populations that have been farming for a long time (almost since farming was invented) seem to have low rates of alcoholism. Perhaps the farming allowed them to make a lot of alcohol, and the alcoholics tended be selected against when a lot of alcohol was available.

    I’m just wondering how the discovery of these ancient Swedes being lactose intolerant fits in with the theory of them being more recently descended from hunter gatherers than southern Europeans.

  • John Emerson

    I have been told that Swedes may have a higher propensity to alcoholism, but expressed alcoholism (active alcoholism) is not especially high. The government works hard to make heavy drinking inconvenient. (This is a factual question; I trust my source but haven’t seen his source.)

    Regarding Jews, they may have a genetic protection from alcoholism, but I’ve been told by a Jewish friend that in a Jewish family, if one member shows any serious signs (daily drinking, drinking large quantities, or visible drunkenness) every other member of the family will say something sooner or later. Whereas in my small town midwestere German-Scandinavian-Yankee culture, it’s OK to brag in a joking way about drinking but almost taboo to suggest so someone that they have a problem. “Pretending it didn’t happen” is common or euphemisms like “Bob had a bad night on Saturday”.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    I’m wondering if people in northern Europe are more recently descended from hunter gatherers than people in southern Europe. Or are the people now living in northern Europe descended entirely from farming populations that moved there from southern Europe?

    i think northern europeans are a mix of both, though the question is how much of a mix. the evidence is slightly (IMO) pointing now to the replacement of the indigenes, though i think the replacement might have been from the east, south or west (westerners who came from the south).

    i think the issue re: alcoholism could be both ancestry or recency of adaptation. fermenting seems to have been more industrialized in the south a lot longer; the gauls imported wine from the romans and greek colonists.

    john, some of the same is true of italians re: drinking. it seems southern europeans have better ability to metabolize alcohol, and, their public drinking culture emphasizes more restraint and self-control. probably some interaction going on.

  • Melykin

    As someone who has at least 2 alcoholics in my close family, I can assure you that having family members “say something” will not cure alcoholism any more than it will cure cancer.

    It is a popular theory that Italians have less alcoholism because they have been introduced to alcohol as teenagers and learned how to handle it. This argument is nonsense. Natives on reserves in Canada start drinking when they are very young–10 or 11 years in some cases. Typically alcoholics start drinking by the time they are 13 or 14, much earlier on average than people who do not become alcoholics. Saying you can prevent alcoholism by teaching teenagers how to drink makes about as much sense as saying you can prevent type 1 diabetes by teaching kids how to eat sugar. Adoption and twin studies have shown it is mostly genetic.

  • John Emerson

    Sample of two, Melykin? And you wait until they’re alcoholic and then you talk to them?

    No one says that early drinking prevents alcoholism. What they say is that people who learn to drink gradually when young, in a family context, sometimes in a religious context, and with meals are less likely to become alcoholic. And what I just said was that in families where the least little sign of alcoholism is nipped in the bud, alcoholism is less likely.

    The drinking pattern that especially leads to alcoholism is guys drinking in a group away from everyone else, where drinking is escapist and part of a macho contest.

    I don’t know what your agenda is but you haven’t made your point.

  • John Emerson

    There are enormous differences in drinking patterns of Chinese and Japanese which as far as I know are not correlated with genetic differences.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    Adoption and twin studies have shown it is mostly genetic.

    you’re using these wrong in your argument fwiw. many genetic predispositions manifest themselves in a cultural context. that’s obvious. this is like megan mcardle’s contention that you can’t stop the impending ubiquity of obesity because BMI is highly heritable.

  • John Emerson

    I might add that American liquor laws reinforce one aspect of elcoholic drinking pattersn. In drinking cultures you’re not really a man or “one of the guys” until you’re drinking with them in the buddy group, so heavy drinking becomes a rite of passage.

  • John Emerson

    And, I forget to say, by setting the drinking age at adulthood, the right of passage is reinforced. Though people do cheat.

  • Melykin

    Razib wrote: you’re using these wrong in your argument fwiw. many genetic predispositions manifest themselves in a cultural context. that’s obvious. this is like megan mcardle’s contention that you can’t stop the impending ubiquity of obesity because BMI is highly heritable
    ———————————-
    I understand that if a person has a tendency to alcoholism that it will not cause a problem unless the person has access to alcohol. Is that what you are saying? What is the point about the BMI? Likely some people do inherit a tendency towards obesity. You don’t agree?

    What do you think of Nicolas Martin’s work? He has been doing twin studies in Australia for years. Here is a quote from an interview with him:
    ——————–
    Q. It seems that a lot of people don’t want to believe that alcoholism might be genetic, and others say it simply isn’t so. Would you like to comment?

    A. (Nicolas Martin) Of course this gets tied up with a lot of moral and religious attitudes, and in a way that’s not necessarily very helpful. I think what people fear when they talk about genetic contributions is that it absolves people of individual responsibility for their own behaviour, undermines the idea that they can have free will and can control their impulses, and so on. People are perfectly entitled to have those views, but I think it is helpful, considering the genetic aspects in this condition, which I think are pretty indisputable, to recognise that in fact some people will have a lot more difficulty controlling their impulses and behaviour than others. It’s probably very easy for somebody who has absolutely no genetic predisposition towards this sort of behaviour to be very moralistic, but unless they’ve actually experienced the difficulty and pain of people who do have genetic predisposition towards addiction they really have no idea.

    http://www.abc.net.au/quantum/poison/alcohol/nick.htm

  • Melykin

    John Emerson wrote: “What they say is that people who learn to drink gradually when young, in a family context, sometimes in a religious context, and with meals are less likely to become alcoholic.”
    ————————

    I think it is true that people who drink wine with their families as teenagers are less likely to become alcoholics than people who don’t. My theory of why this is so is that families of alcoholics do not serve wine with meals. Years of strife and difficulty and failed attempts to quit drinking have lead to all visible alcohol being banished from the home. Meanwhile the alcoholic is probably drinking from a bottle in a paper bag in the corner of the basement.
    The families that DO serve wine with meals most likely have no alcoholics living with them, so there is less likely to be a tendency to it running in the family. Hence the children are less likely to become alcoholic.

    We both see a correlation between wine being served in a family and a lack of alcoholism. We just have different explanations for how the correlation comes about.

    You also wrote: “ I just said was that in families where the least little sign of alcoholism is nipped in the bud, alcoholism is less likely”
    ————————-
    I wish this were true, but it just isn’t. Family members cannot stop a person’s decent into alcoholism any more than they can stop a freight train. I am not basing this statement only on my own experience but on the experience of many thousands of people in organizations such as Al Anon.

  • Melykin

    Here is a link to Nicholas Martin’s home page:
    http://www.qimr.edu.au/research/labs/nickm/index.html

    I misspelled his name in the earlier post. (left the h out of Nicholas)

    By the way Razib, why did you put quotes around “Swedes” and “Lactose Intolerant” in the title of this post? Is this an example of scare quotes?
    http://en.wikipedia.org/wiki/Scare_quotes

  • http://blogs.discovermagazine.com/gnxp Razib Khan


    I understand that if a person has a tendency to alcoholism that it will not cause a problem unless the person has access to alcohol. Is that what you are saying? What is the point about the BMI? Likely some people do inherit a tendency towards obesity. You don’t agree

    do you read my blog at all? or are you so new that you don’t know that you’re using heritability like a sledgehammer?

    first, if you don’t understand why i think you’re being unsubtle, read this:

    http://blogs.discovermagazine.com/gnxp/2009/07/heritability-of-height-vs-weight/

    if that doesn’t make sense to you, read this:

    http://en.wikipedia.org/wiki/Norm_of_reaction

    finally, don’t talk to me like i’m a retard. seriously dude. you shouldn’t be reading my weblog if you think i’m a retard (i.e., if i thought obesity had no genetic component of variation, yeah, i’d be a retard, so you’re asking if i’m a retard if you are asking if i think obesity doesn’t have a genetic component).

    john is right, culture matters in the expression of a heritable trait like alcoholism where genetic variation works over cultural preconditions. the prevalence of alcoholism across the old soviet vs. finnish border in the 1990s was a classic case; both areas had equal prevalence in the early 20th century but went in different directions through different social policies and aspects of cultural evolution.

  • Melykin

    Sorry. I didn’t intend to give offense. Have you got a link about alcoholism on the Finnish soviet border? It sounds interesting. I’ve read that the Scandinavian countries tried to keep a lid on alcoholism by placing a very high tax on it, but this system isn’t working so well now that they have joined the EU.

    I read the links you supplied. I don’t see why it matters, from a practical point of view, whether genes are directly causing disease, or whether they are indirectly causing it by influencing behaviour and environment, which in turn causes the disease. It doesn’t make the disease any easier to control unless you put people in some sort of locked institution where you can control their behaviour and environment. Locking people up because of disease seems to have gone out of fashion. If we could somehow make alcohol and high fat/high sugar foods (and the knowledge of how to make them) vanish from the earth, then all the alcoholics and obese people would be cured. No matter how true this may be, I don’t see how it is useful.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    or whether they are indirectly causing it by influencing behaviour and environment

    because culture mediates the correlations between genes and behavior which are ‘indirect.’ your idea that you have to lock people up is totally ridiculous, there are plenty of ways you can ‘nudge’ people, and cultural context is how it happens. that’s why people tend to seem to be influenced by peer groups in terms of their weight.

    If we could somehow make alcohol and high fat/high sugar foods (and the knowledge of how to make them) vanish from the earth, then all the alcoholics and obese people would be cured.

    if heritability of obesity in japan and the USA are the same, can you understand why i’m saying the norm of reaction matters? or how alcoholism changed after the shift from hard liquor to beer in the USA in the 1850s. see how culture is that norm of reaction?

    this isn’t too hard.

    here’s an article on the difference along the finnish-russian border circa 2000:
    http://www.nytimes.com/2000/12/03/world/an-ailing-russia-lives-a-tough-life-that-s-getting-shorter.html?scp=1&sq=finland%20expectancy%20%20russia&st=cse&pagewanted=print

    again, heritability may be similar on both sides of the border, but median values differ.

    sorry if i sounded like an asshole above, but i’ve had this discussion so many times i’m really sick of it. to really discussion the genetics of behavior you need to talk about the issues in a subtle manner.

  • Melykin

    Maybe the fact that very cheap bootleg liquor is readily available in Russia is contributing towards the very high rate of alcohol problems. Finland has had tight government controls on the sale of alcohol and high taxes on its. Since joining the EU they have been forced into lowering the taxes and control, and have subsequently seen an increase in alcohol related deaths.

    This 2006 article says alcohol is the number one cause of death in Finland:
    http://news.bbc.co.uk/2/hi/europe/6106570.stm

    When environment is seen to effect prevalence of alcohol problems, the “environment” is the state or country, or the society as a whole. When alcohol can be obtained easily and cheaply, and is socially acceptable, there are more problems with alcoholism (other things being equal).

    I have never seen evidence that suggests environment at the level of the household or family has an influence on alcoholism. The twin and adoption studies have in fact shown that the family environment has little influence. So the suggestion of commentator John Emerson that alcoholism can be discouraged by serving wine with meals to teenagers has no basis in science. It is an old wives tale that I have heard many many times. And his suggestion that alcoholism can be “nipped in the bud” by giving the individual a good talking too is absurd, though I’m sure it is an idea that is widely held by people with no alcoholic relatives. It is disappointing to see these misconceptions being put forth and defended in a science blog.

    There is much misinformation and misunderstanding of alcoholism . Many people believe it is not a disease but a moral failing. Nick Martin addresses this in the interview I linked to above. Most people believe alcoholism is learned or caused by abuse or neglect of the parents. This has been discounted by adoption studies. The belief has likely taken hold because of the observation that children of alcoholics have a tendency to become alcoholics. This is a spurious relationship because the parents’ genes for alcoholism are causing both the alcoholic environment and the alcoholism in the children. This sort passive gene-environment correlation is described in one of the links in your heritability-weight blog:
    —————————–
    “Passive gene-environment correlation refers to the association between the genotype a child inherits from her parents and the environment in which the child is raised. Parents create a home environment that is influenced by their own heritable characteristics. Biological parents also pass on genetic material to their children. When the children’s genotype also influences their behavioral or cognitive outcomes, the result can be a spurious relationship between environment and outcome. For example, because parents who have histories of antisocial behavior (which is moderately heritable) are at elevated risk of abusing their children, a case can be made for saying that maltreatment may be a marker for genetic risk that parents transmit to children rather than a causal risk factor for children’s conduct problems.”

    http://en.wikipedia.org/wiki/Gene-environment_correlation

    The observation that some ethnic groups have a higher prevalence of alcoholism puts a damper on genetic research in this area in Canada. The only socially acceptable explanation for the high rate of alcoholism among aboriginals is that it is caused by racism, colonialism and residential schools. There is no science behind these explanation, but they are politically correct, and apparently that is all that matters.

    Sorry if I am being obsessive and annoying about this.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    i was pretty sure john was nodding to the *culture* of drinking in italy, since that’s what i initially pointed to. though he can clarify. yes, i think family-level environmental effects are probably weak.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    re: quotes, swede is an anachronism. lactose intolerance is an example of a term which emerged cuz of eurocentrism, as lactose tolerance is the weird state.

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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com

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