Over generations, religion shapes genetics

Connor Wood

In the United States, religion is usually said to be a personal affair – one’s own private decision about how and what to believe. But this remarkably private and individualistic approach is somewhat odd when compared with the vast majority of cultures and religions throughout history. Far more often, religion has been a public affiliation, determining cultural identities, affecting marriage and family choices, and defining groups in relation to each other. A fascinating recent study published in PLOS Genetics shows just how inextricable religion often is from culture, finding that religious identity has decisively shaped the genetic landscape of the Levant – so decisively, in fact, that Lebanese Muslims are more closely related to fellow Muslims from Morocco or Yemen than they are to their Christian or Jewish compatriots.

The Levant is an area of land that roughly corresponds to modern-day Israel, Jordan, Palestine, Lebanon, and Syria. One of the most religiously diverse regions in the world, the Levant is a crossroads for all three of the major monotheistic religions – Christianity, Islam, and Judaism – and has played a central role in the development of human agriculture and urban culture. Each of the three monotheisms is either historically rooted in the Levant, as in the cases of Christianity and Judaism, or claims areas of the Levant as historically sacred (the Temple Mount in Jerusalem is one of the three most sacred sites in Islam). What’s more, several smaller religions find their origins in the region, including the Druze, an offshoot from Islam that emphasizes the inexpressibility of God’s nature and allows no conversion from other religions.

Against this fantastically diverse religious backdrop, a multinational team of researchers led by Marc Haber of Pompeu Fabra University set out to discover whether the religious distinctions between groups in the Levant might be reflected in the DNA of the people who lived there. Using a collection of genetic samples from more than 1,300 Lebanese residents, the researchers found that single-nucleotide polymorphisms – the most basic measure of differences between DNA in individuals – clustered in the Lebanese population according to religious identification, such that Lebanese Christians formed a single genetic cluster, Muslims their separate cluster, and Druze yet another cluster. This finding implied pretty strongly that marriage traditions in Lebanon mostly broke down along religious lines, with Christians primarily marrying only other Christians, Muslims marrying Muslims, and so forth.

The researchers next took their investigations a step further, including genetic data from all around the Levant and the non-American world in their second round. The endogamous (non-intermarrying) character of Lebanese Christians, Druze, and Muslims persisted in this analysis, but something new showed up as well: Lebanese Muslims, in addition to being relatively genetically isolated from their Christian, Druze, and Jewish countrymen, actually showed significantly genetic similarities with fellow Muslims from far-flung groups like Saudis and Bedouins. Meanwhile, Ashkenazi Jews showed significant genetic relatedness with people from Eastern Europe and the Causasus – an unsurprising finding that reflects the historical interlinkage between Ashkenazi Jews and European culture.

Finally, Haber and his colleagues used a different measure of genetic diversity, haplotype reconstruction, to determine approximately when the various populations in the Levant parted ways from each other genetically. Haplotypes are composed of many nucleotide sequences and are passed down intact as units from parents to children, thus forming one of the basic loci at which genetic mutation and selection does its work. Because there is significant diversity in haplotypes across populations, Haber and his fellow researchers were able to generate a “family tree” that clustered groups of people according to how similar or dissimilar their genomes were at a particular haplotype. More specifically, the researchers used a simulation to break down the haplotype of each individual into “chunks,” and then tested the simulation to see how many “chunks” of haplotypes from different ethnic or geographic groups it would take to reassemble the original. The more chunks it took, the less related the individuals in question were.

The team used the results of the simulation to produce a genetic family tree. Unsurprisingly, religious groups tended to cluster together: both Ashkenazi and Sephardic Jews grouped together on a single branch of the tree, while Druze from different countries all similarly clustered on their own branch. Fascinatingly, the Muslim populations from around the Levant were more genetically similar to Muslim groups from distant countries than they were to their Christian or Druze neighbors. As the authors put it,

“The predominantly Muslim populations of Syrians, Palestinians and Jordanians cluster on branches with other Muslim populations as distant as Morocco and Yemen…Jordanians, Palestinians, and Syrians receive more (haplotype) chunks from sub-Saharan Africans and from Middle Easterners compared with other Levantines.”

Using a statistical method designed to estimate the amount of time lapsed since populations diverged genetically, Haber and his colleagues then calculated how long it had been since each Levantine group had last intermixed with sub-Saharan African populations. The results showed that Christians had ceased intermixing with African populations approximately 2,300 to 2,000 years ago – times marked by the rise of Hellenic rulership in the Mediterranean and the advent of Christianity, respectively. Druze populations had last intermixed with sub-Saharan African genes around 1,200 to 1,000 years ago, precisely when the Druze offshoot faith arose. And Muslims ceased intermingling with African populations around 600 years ago, which corresponds roughly to the rise of the Muslim Ottoman Empire and the fall of Constantinople.

Particularly with the Levantine Druze, these results show that religious identification can have concrete – and immediate – effects on everything from geographic mobility to intermarriage. What’s most interesting about this research, though, isn’t necessarily the findings themselves; in fact, it’s not particularly surprising to learn that religious groups are genetically isolated from one another, since anyone can see that religious believers generally marry other believers of the same stripe. The takeaway point, instead, is that religion is not only an abstract thing, a set of beliefs or propositions. By looking at the actual chromosomes of real people – their basic, biological essences – the researchers found that religious identity was literally a shaper of who we are. These data tell a more compelling story about religious identity, a story with roots in people’s physical beings. And that story is hard to ignore.

Read the original article at PLOS Genetics here.

  • http://triangulations.wordpress.com/ Sabio Lantz

    This study confirms one of the ugly aspects of religion — exclusivism: “Remember, we don’t marry those type of people.” It shows religion’s atavistic tribal function.

    • Rob Henderson

      Or it could show that people prefer to marry other people who have similar backgrounds, moral codes, and outlooks on life.

      • JenellYB

        Rob, I agree this is probably the stronger influence. I think it does deeper than that, though, into even seemingly minor details of how people do ordinary daily life things and respond to ordinary daily life events that they pass down through generations, many we don’t even give much thought to. Talk to a few couples that have married across just socio-economic, regional lifestyle, or immigrant lines and its amazing all the little everyday things they’ve discovered their partner and families do very differently. Even subtle differences in how they use language, handle disputes and disagreements, commonly arise out of different background traditions.
        But there is also simple convenient proximity, young people are more likely to meet and get to know and marry someone from a similar community/sub-cultural group, than the ‘exotic stranger.’

    • connorwood

      Thanks for your comment. Rob Henderson puts it well. I agree that the tribalizing function of religion can be frustrating sometimes, but let me take Rob’s observation one step further: If people married without regard to culture, backgrounds, language, beliefs, or any of the other things that help comprise religion, there would be no reason to marry any one person instead of any other. So the type of universalistic world you’re implicitly advocating would be a world without difference or local character of any kind, and, honestly, not a world I’d like to live in.

      • http://triangulations.wordpress.com/ Sabio Lantz

        @ Rob Henderson,
        The “don’t marry them!” ethic is huge. I have seen it and heard it for decades. I hope it continues to break down and I think it will — and with it, religious exclusivism and specialism.

        @ connorwood

        Really?

        If married someone because they were trustworthy, fascinating or fun, I wouldn’t have to teach out children to avoid someone of a color, a culture, a language or religion. I could teach them to look for some of those non-tribal, non-exclusive elements.

        To say that it is all the same is a ridiculous blur and poor understanding of how people work. Sounds like you are going out of your way to defend religion. When say “I agree that the tribalizing function of religion can be frustrating sometimes” — you are playing down millenium of murderous, horrible behavior under the rubric of “frustrating sometimes”.

        • connorwood

          Sabio,

          I’m not defending religion, I’m defending culture. If everyone married without any regard to their partners’ cultural background, we would end up with a generalized, bland, worldwide cultural pudding – sort of like the cultural version of an American suburban strip. In the process, we’d lose all of the traditions, languages, and sources of meaning that make life worthwhile.

          Let’s look at your claim about how you’d raise your children. You say that you’d teach them to choose spouses because they’re “trustworthy, fascinating or fun,” rather than because they follow a certain religion or belong to a certain culture. But who decides what’s “fascinating?” Your culture does. For a Lakota Sioux, the traits, habits, and quirks that make another person fascinating will almost certainly be different from the traits that make someone fascinating for a French person, or a Korean. A French guy might find your knowledge of the poet Beaudelaire “fascinating,” while a Korean might not be so enthusiastic about your French Bohemian poetry. It’s our cultural backgrounds that shape our aesthetics, preferences, and personalities. “Trustworthy,” “fascinating,” and “fun” are not universal traits, hovering out there for members of all cultures to see. They are cultural particulars and mean different things in different contexts.

          Therefore, to say that everyone should just look to traits like trustworthiness when choosing their mates is actually to say, “Everyone should use the categories that MY culture uses, and in the exact same ways, in order to evaluate one another.” In other words, you’re not arguing that people shouldn’t be culturally or religiously exclusive after all – you’re actually saying that everyone should follow YOUR culture.

          • http://triangulations.wordpress.com/ Sabio Lantz

            @ Connorwood,

            You are missing, and misquoting my points.

            Cultural Inter-Marriage Taboos are bad: Taboos which threaten a child with rejection if they were to marry outside that culture (be it religion, race, language…) are bad.

            I absolutely did not say: “Everyone should use the category MY culture uses …” Your argument style here is tell-tale. I will not teach my children to reject another person for their language, what holidays they value, what religion they have, what hobbies they have. I will teach, instead, deeper, non-exclusive values. If you can not see the difference, there is no point to continue the conversation.

            When different cultures intermingle, new cultures emerge. The point is that non-exclusivity is very valuable. One can raise one within a set of values and aesthetics without teaching exclusivity.

            I won’t even get into the problem with the overused and prescriptive use of the word “culture”.

            Recent Pew poll shows >85 of Egyptians feel that if someone deconverts from Islam they should be killed. It is near 80% for Palestinians. And the list goes on. Evangelicals (and many other Christians) tell their children that “unequal yoking” is horrible and that the unbelievable spouse with not only suffer hell but drag them possibly into eternal torment.

            Many Chinese and Indian parents do everything they can to be sure their children don’t marry outside their culture/race.

            These things are ugly. If you feel these are wonderful things that protect us from a horrible “American suburban strip” [sic], then we have no common ground for discussion.

          • connorwood

            Your tone is a little harsh here. If you want to have a discussion on the contents of the article, fine. But saying things like “If you [insert belief here], then we have no grounds for discussion” is actually pretty rude. Please be more polite in the future.

            Next, it is absolutely not okay to threaten death or anything like it for deconversion. Period.

            However, what I was saying about culture still stands – you may tell your children not to reject potential spouses because of their religion or holidays, but the fact is that we are always going to be drawn to people who share commonalities with us. An example: my girlfriend and I like a lot of the same 80s and 90s British and American rock music. This is because we were children of the same culture at the same time period, and hearing the music of that culture makes us feel warm and fuzzy about one another. The point is that many of the things that draw couples together are based on a shared cultural understanding about what’s important or desirable in life, what’s “fun,” what’s “good,” etc. And what’s “fun” or “good” is not the same across cultures. Being drawn to someone who has similar ideas about these things isn’t morally wrong or xenophobic; it’s human nature. This preference for shared worldview is as much, or more, responsible for religious endogamy (marriage within a group) as explicit prohibitions against marrying outsiders.

            Again, if you respond, please do so politely.

      • http://triangulations.wordpress.com/ Sabio Lantz

        Well, I am glad you feel that teaching that killing someone for leaving the faith is wrong — no matter how much warm and fuzzy the believers tend to share. So that takes care of much of Muslim cultural teaching in many countries that you disagree with. But Muslims also forbid their women marrying nonbeliever men. Muslim men may may nonMuslim women but only under strict conditions:

        http://qa.sunnipath.com/issue_view.asp?HD=1&ID=2267&CATE=10

        Do you feel that commanding believers that they should not marry unbelievers is wrong. (2 Cor 6:14 — Do not be yoked together with unbelievers. For what do righteousness and wickedness have in common? Or what fellowship can light have with darkness?)

        Yahweh commands Jews to stay away from wicked non-believers or he will destroy them: Deut 7:3-4 3 Do not intermarry with them. Do not give your daughters to their sons or take their daughters for your sons, 4 for they will turn your children away from following me to serve other gods, and the Lord’s anger will burn against you and will quickly destroy you.

        So, there you have three major monotheist religions demanding NO intermarriage.

        Do you think these edicts to stop marriage with such strong violent threats and condemning of others is OK because, afterall, it will preserve “warm and fuzzy” sharings and preserve precious religious culture so that the world does not look like an American strip mall?

        That is my question. Do you condemn these attitudes above?

        • connorwood

          Thanks for your question. It’s a difficult one to answer. As a cosmopolitan, educated person who has always distrusted excessive tribalism, my first response is to say, “Yeah, those attitudes are bad.”

          But as someone who has spent many years studying religion from biological, cultural, theological, evolutionary, and psychological angles, I can’t make such simple judgments anymore (which is sometimes very frustrating). To try to explain why, let me use an example. The well-regarded evolutionary biologist D.S. Wilson makes a very good argument for the NECESSITY of Jewish rules against marrying non-Jews. In every case around the world where Jewish communities have remained closed off, marriage-wise, from surrounding cultures, those communities have thrived. Almost universally, exclusive Jewish diaspora communities have better literacy rates, lower child mortality rates, more education, higher income, and better social cohesion than the surrounding secular or Christian societies. But when Jewish communities start intermarrying with the surrounding culture, those better outcomes start dissipating – fast. A Jewish community that intermarries with non-Jews becomes a secular community very quickly, and loses virtually all of the benefits of tight social bonds, religiously based emphasis on education, etc. By remaining endogamous, Jewish communities actually insulate themselves from influences that seem to genuinely damage their way of life.

          Take that example agains the background of 2000 years of Jewish diaspora, during which Jewish culture remained healthy and intact while surrounded by foreign, often hostile cultures. The fact that Jewish culture survived this diaspore is literally unprecedented in world history. It’s astounding. And the reason it worked is because Jews refused to allow themselves to blend too much with their host cultures, even as they peaceably conducted trade and business with them.

          One of the most frustrating things for me about religion is that is really does have positive benefits, including encouraging healthy behaviors (e.g., Mormon laws against drinking alcohol or taking drugs), making people feel connected to a community, and helping to regulate potentially destructive appetites and instincts. But these benefits seem to be very, very hard to separate from the tribalism, exclusivism, and various forms of unfairness that I find really, well, horrible. A lot of my research is driven by the quest to understand how religions can provide the benefits without succumbing to the fatal flaws. I expect that I have my life’s work cut out for me.

  • Arakiba

    A subtitle for this article could be “Inbreeding Made Easy”, especially for smaller religions.

    • connorwood

      There are two billion Christians, a billion Muslims, and well over a million Druze in the world. Inbreeding is not the major takeaway point here.

  • Jerry Lynch

    Why not genetic predilection instead of cultural exclusivity? Are the features of DNA mentioned in any way influential on behavior? Would the genetic markers built up by this exclusivity factor become a character predisposition? Just curious.

    • connorwood

      Jerry, do you mean a genetic predilection to prefer people of one’s own tribe? I would think that hypothesis doesn’t stand up against the sudden divergence of the Druze genetic profile from other populations right after Druze religion began.

      The original paper doesn’t say which phenotypes the particular gene clusters in question were thought to be responsible for. If they did affect behavior – like making people slightly more outgoing, or creative, or conscientious – then people within that group would probably start to develop a preference for those behavioral traits. That would then reinforce the cultural exclusivism, since both religious guidelines AND gut-level preferences would prod people away from marrying outside the faith. This would be an excellent example of the gene-culture interaction in evolution, which I think plays an important part in religion.


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