Razib Khan One-stop-shopping for all of my content

December 9, 2018

A genetic history of the human race is not controversial science nor is it fraught

Filed under: Elizabeth Warren,Personal genomics — Razib Khan @ 2:06 pm

Recently I was talking to a journalist about genetic genealogy, and we both agreed that soon Christine Kenneally’s The Invisible History of the Human Race: How DNA and History Shape Our Identities and Our Futures will need an update. Though published in 2015, much of the research in The Invisible History of the Human Race dates to much earlier.  In the last few years, personal genomics has gone from a sector of millions to tens of millions. In years after 2020 it will go to hundreds of millions.

And yet I’m not sure the educated public is ready to understand what a genomic future is going to look like.

This is why I think that the Elizabeth Warren DNA story is important to get right. The reality is that this isn’t really about Elizabeth Warren’s ancestry, it’s a story at the intersection of high politics and culture wars, and genetics is getting caught in the undertow. Recently I heard Ben Shapiro comment that Warren likely had “maybe 1/1024th Native American.” Actually, I think it’s very likely she has 0.5 to 1% Native American ancestry (read this Elizabeth Warren DNA story“>post why) Not to be trite, but facts don’t care about Ben Shapiro’s feelings. I know he’s not a fan of Warren, but he shouldn’t be laundering misrepresentations.

Even in the comments of this website motivated reasoning cropped up when the original Warren story became a national sensation. Many on the Right side of the spectrum laughed at the results and interpreted them in the least generous terms. The falsehoods and misunderstandings promoted by the media, often inadvertently because most journalists don’t have the skills to navigate the science, were injected into the conservative memesphere.  Shapiro has admitted, to his own chagrin, his lack of science background, and I suspect if I explained it to him he wouldn’t use “maybe 1/1024th Native American” line. He doesn’t need to. If you are a conservative there are many reasons to be critical of Elizabeth Warren.

But I can’t blame Shapiro too much. He was reacting to this story in The New York Times, Elizabeth Warren Stands by DNA Test. But Around Her, Worries Abound. In this piece, the attacks on Warren are coming from the Left and Native American activists. There is a real story here. The Boston Globe has published an editorial warning her not to run. The air has changed around her.

From the piece in The Times:

Warren’s presidential ambitions, she has yet to allay criticism from grass-roots progressive groups, liberal political operatives and other potential 2020 allies who complain that she put too much emphasis on the controversial field of racial science — and, in doing so, played into Mr. Trump’s hands.

Ms. Warren’s allies also say she unintentionally made a bigger mistake in treading too far into the fraught area of racial science — a field that has, at times, been used to justify the subjugation of racial minorities and Native Americans.

There is “racial science” like there is “evolution science” or “Creation science.” The term is not used by any scientist that I know of, but comes up by critics and polemicists. The New York Times, whether consciously or not, is going to convince a lot of scientifically illiterate people who don’t read their science pages that there is a field of “racial science” (using the term “race science” liberally is a thing on the Left…reminds me of social conservatives who used to call everyone who was not an evangelical Protestant a “non-Christian”)

Here’s what went on in the Warren case is:

  1. Not scientifically controversial
  2. But scientifically new

Here is a review, A comprehensive survey of models for dissecting local ancestry deconvolution in human genome which looks at “20 methods or tools to deconvolve local ancestry.” There may be disagreement on the best method for various reasons, but there is no disagreement that local ancestry deconvolution is possible. It is not controversial. In fact, it is rather important in areas such as admixture mapping for diseases.

The science isn’t that hard to explain at a high level. The figure to the left is from a new paper that recently came on the genetics of the New World (using ancient DNA). What you see is that some human populations are isolated from other human populations. For example, the last common substantial ancestry of Native American populations before 1492 and Northern Europeans dates to the period between 20,000 to 40,000 years ago.

Tens of thousands of years of genetic separation result in genetic distinctiveness. This is a standard old population genetic model. When populations come back together and mix, that daughter population is clearly going to be genetically a mix between the two parent populations. But the human genome is a sequence of three billion distinct base pairs, and the mixing exhibits discrete patterns within the genome.

Humans are diploid, which means we have two copies of each gene. These genes are aligned along homologous chromosomes. One homolog you inherit from the father and one homolog you inherit from the mother. These two homologs are the basis for Mendel’s Law of Segregation.

When sex cells, sperm and eggs, are formed they carry only one of the homologs. They are haploid, with single gene copies. If they weren’t, you’d end up tetraploid instead of diploid. You get one gene copy from the mother and one gene copy from the father.

But, before the formation of sex cells, during meoisis, the homologs undergo recombination. In humans that means that there is swapping between stretches of homologous chromosomes. The average human has between 20 and 40 recombination events across the genome. A concrete way to think about it is that the individual who is producing sperm or egg is taking the chromosomes they inherited from their parents, and mixing them together, so the final set of chromosomes are a synthetic combination of the chromosomes of grandparents.

Purple segments half-identical to paternal grandfather

To make this concrete, to the left is a partial depiction of one of my children’s chromosomes, and the relatedness to my father. The purple regions are genomic stretches where the child is half-identical to the paternal grandfather. The light gray sections have no genetic descent from my father. The reason is that one of the homologs is from the maternal side. The other homolog is from me, and could be from either my father or my mother. Where the purple alternates with light gray, you see clearly where recombination events happened, as maternal and paternal homologs broke and paired together to produce sperm with novel chromosomes (e.g., my contributed chromosome 11 is 90% my father, 10% my mother…while chromosome 19 is more balanced.

But that’s not the only way to look at recombinations. To the right is an ancestry painting for 23andMe from a friend of mine who is ~25% East Asian and ~75% Northern European. On their chromosome you see two homologs. The blue segments are Northern European. The dark brown segments are East Asian. Notice the alternation between European and East Asian on one of the homologs: this chromosome is almost certainly from the parent who is 50% East Asian and 50% European. There was a recombination event where an “East Asian” homolog, inherited from the parent of East Asian origin, recombined with the “European” homolog, inherited from the parent of European origin.

The resultant chromosome is something new in a physical sequence, with alternating segments of East Asian and European ancestry. Just as the whole genome has an imprint of the genetic history of a population, so sequences of the genome also exhibit distinctiveness due to their origins. Because each generation introduces recombination events, the lengths of these distinct ancestry blocks can tell you how many generations in the past the admixture may have happened.

That’s the theory. The new aspect is that genomic technology have allowed science to assess patterns of local ancestry to a much greater extent than was possible even 15 years ago. With hundreds of thousands of genomic positions, variants, scientists are now able to map regions of the genome to an incredible level of granularity, deploying theoretical understanding of Mendelian and population genetics that dates back to the 20th century.

To look at Elizabeth Warren’s genome, and discover that a small segment of a particular length derives from a Native American population, is not a “controversial field of racial science.” This sort of analysis is now becoming de rigueur in much of medical genetics in larger part because population history has a major impact on disease risk susceptibility. To be fair, doing a local ancestry deconvolution on populations which are much, much, closer genetically due to recent shared history is difficult. But Warren’s is not one of those cases!

Honestly, I don’t know what the outcome of The New York Times calling this “racial science” is going to be, seeing as how it seems likely in the next few years >100 million Americans will have likely done ancestry tests. Many scientists, fairly, do criticize of the interpretations of these tests, and how the public perceives them. But the underlying models and methods are workaday.

It is the interpretation, and how they interact with social and political values, is fraught. The link in the phrase “controversial field of racial scienceactually goes to an article where social and political commentators and activists react to Warren’s decision to take the DNA test. There is no discussion of the science at all. It’s controversial because of what they believe the implications are, not because the science is faulty or unsound.

For example, many (though not all) Native Americans object to the idea of using genetic science to shed light on the status of particular individuals as Native American or not. The decision to take this DNA test, in an environment where many already privately grumbled about Warren’s claims, was obviously clearly a political and public relations misstep. But that does not speak to whether the science itself is sound or unsound.

Conservatives will be highly skeptical of Warren because of her policy positions. And, if the above article is correct, it seems that some of the Left is now against her on the grounds of her impolitic foray into Native American identity. That is all fine, and not much of a concern of mine. But when non-science journalists get their hands on a science story, they tend to mess it up, and that is a problem in the long-term. The sands of politics and society are protean, and always shifting. Science is something more solid, and we should not try to muddy the waters.

April 29, 2012

Elizabeth Warren, Native American

Filed under: Elizabeth Warren,Personal genomics — Razib Khan @ 8:42 am


Elizabeth Warren, Native American

It has come to my attention that Elizabeth Warren, who is running for a Senate seat in Massachusetts, claims Native American ancestry. This did not surprise me. Warren is from Oklahoma, where nearly 10% of the population claims some Native American ancestry. The problem, as it is, is that apparently Harvard claimed Warren as a minority faculty member during its periodical head counts. Warren “was told through family lore that her maternal parents were from the Cherokee and Delaware tribes.” This is a moderate problem: family lore often is inaccurate. And it also exhibits biases. Nevertheless, I do think we need to be careful about being too skeptical in this case, because of Warren’s roots in Oklahoma. A friend was told that his maternal grandmother was of part Oklahoma Choctaw background, and he had always dismissed this as romantic distortions made to fit 21st century preconceptions and preferences. But when he got his results back from 23andMe there was a notable “Asian” component, and the Native American relative finder came back positive. He asked me to look at his results more deeply, ...

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