In Latter-day Saint thought and history the idea of “believing blood” has racial connotations. The traditional “believing blood” theological model that is (rightfully, in my view) criticized by thinkers such as Armand Mauss in his book All Abraham’s Children goes something like this: certain ethnicities and nations are more amenable to the gospel message because they are the literal descendants of Israel, maybe even Ephraim. (And there’s a whole other post or several to be written on the interesting connection between such Latter-day Saint beliefs and British Israelitism, or the belief that the British are descended from the Lost Ten Tribes, which is one possible logical corollary of this chain of thought that the early Saints were from Britain, Ephraimites are more susceptible to the gospel, therefore British=Ephraim). 

Another (non-racist) variant on this makes sense in terms of 1980s Sunday School population genetics: that Ephraimite/Israelite ancestry is found throughout the world, but retained certain discrete strands within different populations, so that in the same sense that early British converts were the children of Ephraim so too could the aboriginal Australians or Bengalis be who accepted the gospel be.

Except now our understanding of paleodemography is such that if somebody in 2000 BC had a surviving native British descendant, then nearly all of Britain are his descendants since family trees loop in on each other so much. So if your ancestor who embraced the gospel in Liverpool in the 19th century is a descendant of Ephraim, then so is Richard Dawkins.* 

However, while literally, genetically inheriting the spiritual attributes of a particular brother or small Israelite tribe 2,000 years ago is dubious, there’s another way that there does indeed appear to be a “believing blood” dynamic going on, one that I think could shape the future of the world.

Some research is indeed starting to suggest that religiosity is inheritable. For example: 

Freeman, Jason A. “Is apostasy heritable? A behavior genetics study.” Twin Research and Human Genetics 22, no. 2 (2019): 88-94.

Vance, Todd, Hermine H. Maes, and Kenneth S. Kendler. “Genetic and environmental influences on multiple dimensions of religiosity: A twin study.” The Journal of Nervous and Mental Disease 198, no. 10 (2010): 755-761.

Bradshaw, Matt, and Christopher G. Ellison. “Do genetic factors influence religious life? Findings from a behavior genetic analysis of twin siblings.” Journal for the Scientific Study of Religion 47, no. 4 (2008): 529-544.

I’m not aware of any meta-analysis that has been done in regards to effect sizes, but some evidence suggests that it isn’t minor. For example in the Bradshaw and Ellison study above:

 “Specifically, genetic factors explain 19–65 percent of the variation, while environmental influences account for the remaining 35–81 percent depending upon the aspect of religion under investigation.”

So a lot of how religious you are is from the roll of the genetic dice. This makes sense to me, frankly. For example, I’ve long suspected that there’s at least some kind of God belief gene or pathway of genes just because it seems like with belief in some kind of divinity you kind of have it or you don’t. Some people dispositionally, viscerally feel there’s something out there (whether they’re believers in organized religion or not), while for others atheism is the commonsensical default, and this gut-belief comes prior to any sort of argument from first principles. 

(Admittedly, the genetic inheritance of religiosity has not been widely tested cross-culturally, so there are probably some moderating factors at play; so no, I’m not saying that the 99% of Afghans who believe in God all have the God belief gene, just that some of them would be atheist if they were raised in a society that was more amenable to that belief. Still, in general I wouldn’t be surprised if in general religion was heritable to some degree or another even if it heavily moderated by the outside environment). 

So what are the long-term implications of this? In today’s world where sex is disconnected from reproduction, non-believers are having hardly any children. Study after study has found that the religious both desire and have much larger families, even while controlling for income, education, and the like, and that this effect is fairly consistent across cultures and countries where it has been tested. 

Consequently, the implications for the future prevalence of religious genes are obvious (even when disconnected from organized religion: a paper I wrote showed that even non-religious theists have more babies than atheists). Of course, the wheels of human evolution grind slowly, but if these numbers are even approximately correct, both with the genetic inheritance of religiosity and the fertility advantage of the religious, this might be our own version of the famous speckled moths that evolved darker coverings within the blink of an eye (geologic time-wise) in order to adjust to accommodate England’s soot from the Industrial Revolution. 

 I hinted at the possibility of an evolution towards religiosity in the one evo-bio paper I published, but I don’t have the bandwidth to work out the math to come up with some theoretical hypotheses about how much change we’d see and at what rate given a few reasonable premises (maybe a retirement project). Of course, while secularization and revivals ebb and flow with cultural and historical contingency, thus probably drowning out any genetic move towards religiosity in the short or even medium term, in the background there is a good chance that as the non-religious are selecting themselves out of the gene pool we will essentially become a more religious species. In other words; yes, believing blood could be a thing, and it could help determine the future of the world. 

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*This is outside my ken knowledge-wise, so I might be wrong, but I suppose one last variation on this that might have some validity before we get to the “we’re all adopted into the Ten Tribes” (except for some ethnic group in Iraq) stage is that while Abrahamic ancestry is shared around the world (indeed, my understanding is that given population dynamics Abrahamic ancestry could easily literally be in nearly all of the families of the world, as promised by God, except for maybe the occasional super isolated tribe here and there), that there’s still some ebb and flow of which and how many nucleotides from the individual there are floating around (I believe there’s some commentary from President Oaks along these lines in explaining how members of the same family can have different patriarchal blessing lineages), so that while everybody is from Abraham/Ephraim/what have you, some almost stochastically have more genes from that individual than others, again not in the grand sense of some having more Middle Eastern ancestry in general that we can detect like with the Ethiopian Jews, but more specifically about that particular individual 4,000 years ago (although they would also be sharing that DNA strand with a bajillion other individuals). As an example, while Thomas Jefferson is undoubtedly very Celtic/British, and is not discernibly African or Semitic if you were to sequence his entire DNA, his Y chromosome is from the Middle East. I’m not saying that he’s a literal Ephraimite through his paternal line, just using him as an example of how far flung genes can get mixed around.