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Evolution, In the News, Research, Stanford News

Blond ambition: Delving into the work of Stanford biologist David Kingsley

Blond ambition: Delving into the work of Stanford biologist David Kingsley

Thanks to a tiny fish called the stickleback, Stanford developmental biologist David Kingsley, PhD, and his team uncovered the genetic basis for blond hair earlier this year.

Kingsley’s research caught the eye of the team at HHMI Bulletin, which featured his discovery in their fall issue. As described in the piece, Kingsley and fellow researcher Catherine Guenther, PhD, discovered the change in a single point in the genetic sequence outside the gene itself. The discovery prompted a question because the gene, known as KITLG, is involved in many other key processes in developing organisms. Yet Kingsley found the control for hair color acted alone.

“The genetic mechanism that controls blond hair doesn’t alter the biology of any other part of the body. It’s a trait that’s skin deep, and only skin deep,” Kingsley told HHMI.

The HHMI feature also includes a video of Kingsley – above – that provides glimpses into his lab and reveals the sources of his inspiration (as well as his penchant for purchasing telescopes).

And for a Friday giggle, check out his lab members spelling his name with their bodies here.

Becky Bach is a science-writing intern at the Office of Communications and Public Affairs. 

Previously: It’s a blond thing: Stanford researchers suss out molecular basis of hair color, Something fishy: Threespine stickleback genome published by Stanford researchers and Hey guys, sometimes less is really more

Behavioral Science, Evolution, Imaging, Neuroscience, Research, Stanford News, Surgery

In a human brain, knowing a face and naming it are separate worries

In a human brain, knowing a face and naming it are separate worries

Alfred E. Neuman (small)Viewed from the outside, the brain’s two hemispheres look like mirror images of one another. But they’re not. For example, two bilateral brain structures called Wernicke’s area and Broca’s area are essential to language processing in the human brain – but only the ones  in the left hemisphere (at least in the great majority of right-handers’ brains; with lefties it’s a toss-up), although both sides of the brain house those structures.

Now it looks as though that right-left division of labor in our brains applies to face perception, too.

A couple of years ago I wrote and blogged about a startling study by Stanford neuroscientists Josef Parvizi, MD, PhD, and Kalanit Grill-Spector, PhD. The researchers recorded brain activity in epileptic patients who, because their seizures were unresponsive to drug therapy, had undergone a procedure in which a small section of the skulls was removed and plastic packets containing electrodes placed at the surface of the exposed brain. This was done so that, when seizures inevitably occurred, their exact point of origination could be identified. While  patients waited for this to happen, they gave the scientists consent to perform  an experiment.

In that experiment, selective electrical stimulation of another structure in the human brain, the fusiform gyrus, instantly caused a distortion in an experimental subjects’ perception of Parvizi’s face. So much so, in fact, that the subject exclaimed, “You just turned into somebody else. Your face metamorphosed!”

Like Wernicke’s and Broca’s area, the fusiform gyrus is found on each side of the brain. In animal species with brains fairly similar to our own, such as monkeys, stimulation of either the left or right fusiform gyrus appears to induce distorted face perception.

Yet, in a new study of ten such patients, conducted by Parvizi and colleagues and published in the Journal of Neuroscience,  face distortion occurred only when the right fusiform gyrus was stimulated. Other behavioral studies and clinical reports on patients suffering brain damage have shown a relative right-brain advantage in face recognition as well as a predominance of right-side brain lesions in patients with prosopagnosia, or face blindness.

Apparently, the left fusiform gyrus’s job description has changed in the course of our species’ evolution. Humans’ acquisition of language over evolutionary time, the Stanford investigators note, required the redirection of some brain regions’ roles toward speech processing. It seems one piece of that co-opted real estate was the left fusiform gyrus. The scientists suggest (and other studies hint) that along with the lateralization of language processing to the brain’s left hemisphere, face-recognition sites in that hemisphere may have been reassigned to new, language-related functions that nonetheless carry a face-processing connection: for example, retrieving the name of a person whose face you’re looking at, leaving the visual perception of that face to the right hemisphere.

My own right fusiform gyrus has been doing a bang-up job all my life and continues to do so. I wish I could say the same for my left side.

Previously: Metamorphosis: At the push of a button, a familiar face becomes a strange one, Mind-reading in real life: Study shows it can be done (but they’ll have to catch you first), We’ve got your number: Exact spot in brain where numeral recognition takes place revealed and Why memory and  math don’t mix: They require opposing states of the same brain circuitry
Photo by AlienGraffiti

Big data, Evolution, Genetics, In the News, Research, Science, Stanford News

Flies, worms and humans – and the modENCODE Project

Flies, worms and humans - and the modENCODE Project

It’s a big day in comparative biology. Researchers around the country, including Stanford geneticist Michael Snyder, PhD, are publishing the results of a massive collaboration meant to suss out the genomic similarities (and differences) among model organisms like the fruit fly and the laboratory roundworm. A package of four papers, which describe how these organisms control how, when and where they express certain genes to generate the cell types necessary for complex life, appears today in Nature.

From our release:

The research is an extension of the ENCODE, or Encyclopedia of DNA Elements, project that was initiated in 2003. As part of the large collaborative project, which was sponsored by the National Human Genome Research Institute, researchers published more than 4 million regulatory elements found within the human genome in 2012. Known as binding sites, these regions of DNA serve as landing pads for proteins and other molecules known as regulatory factors that control when and how genes are used to make proteins.

The new effort, known as modENCODE, brings a similar analysis to key model organisms like the fly and the worm. Snyder is the senior author of two of the papers published today describing some aspects of the modENCODE project, which has led to the publication, or upcoming publication, of more than 20 papers in a variety of journals. The Nature papers, and the modENCODE project, are summarized in a News and Views article in the journal (subscription required to access all papers).

As Snyder said in our release, “We’re trying to understand the basic principles that govern how genes are turned on and off. The worm and the fly have been the premier model organisms in biology for decades, and have provided the foundation for much of what we’ve learned about human biology. If we can learn how the rules of gene expression evolved over time, we can apply that knowledge to better understand human biology and disease.”

The researchers found that, although the broad strokes of gene regulation are shared among species, there are also significant differences. These differences may help explain why humans walk, flies fly and worms slither, for example:

The wealth of data from the modENCODE project will fuel research projects for decades to come, according to Snyder.

“We now have one of the most complete pictures ever generated of the regulatory regions and factors in several genomes,” said Snyder. “This knowledge will be invaluable to researchers in the field.”

Previously: Scientists announce the completion of the ENCODE project, a massive genome encyclopedia

Autoimmune Disease, Evolution, Immunology, Microbiology, Nutrition, Public Health, Stanford News

Civilization and its dietary (dis)contents: Do modern diets starve our gut-microbial community?

Civilization and its dietary (dis)contents: Do modern diets starve our gut-microbial community?

hunter-gatherer cafe

Our genes have evolved a bit over the last 50,000 years of human evolution, but our diets have evolved a lot. That’s because civilization has transitioned from a hunter-gatherer lifestyle to an agrarian and, more recently and incompletely, to an industrialized one. These days, many of us are living in an information-intensive, symbol-analyzing, button-pushing, fast-food-munching society. This transformation has been accompanied by consequential twists and turns regarding what we eat, and how and when we eat it.

Toss in antibiotics, sedentary lifestyles, and massive improvements in public sanitation and personal hygiene, and now you’re talking about serious shake-ups in how many and which microbes we get exposed to – and how many of which ones wind up inhabiting our gut.

In a review published in Cell Metabolism, Stanford married-microbiologist couple Justin Sonnenburg, PhD, and Erica Sonnenburg, PhD, warn that modern civilization and its dietary contents may be putting our microbial gut communities, and our health, at risk.

[S]tudies in recent years have implicated [dysfunctional gut-bug communities] in a growing list of Western diseases, such as metabolic syndrome, inflammatory bowel disease, and cancer. … The major dietary shifts occurring between the hunter-gatherer lifestyle, early Neolithic farming, and more recently during the Industrial Revolution are reflected in changes in microbial membership within dental tartar of European skeletons throughout these periods. … Traditional societies typically have much lower rates of Western diseases.

Every healthy human harbors an interactive internal ecosystem consisting of something like 1,000 species of intestinal microbes.  As individuals, these resident Lilliputians may be tiny, but what they lack in size they make up in number. Down in the lower part of your large intestine dwell tens of trillions of  single-celled creatures – a good 10 of them for every one of yours. If you could put them all on a scale, they would cumulatively weigh about four pounds. (Your brain weighs three.)

Together they do great things. In a Stanford Medicine article I wrote a few years back, “Caution: Do Not Debug,” I wrote:

The communities of micro-organisms lining or swimming around in our body cavities … work hard for their living. They synthesize biomolecules that manipulate us in ways that are helpful to both them and us. They produce vitamins, repel pathogens, trigger key aspects of our physiological development, educate our immune system, help us digest our food and for the most part get along so well with us and with one other that we forget they’re there.

But when our internal microbes don’t get enough of the right complex carbohydrates (ones we can’t digest and so pass along to our neighbors downstairs), they may be forced to subsist on the fleece of long carbohydrate chains (some call it “mucus”)  lining and guarding the intestinal wall. Weakening that barrier could encourage inflammation.

The Sonnenburgs note that certain types of fatty substances are overwhelmingly the product of carbohydrate fermentation by gut microbes. These substances have been shown to exert numerous anti-inflammatory effects in the body, possibly protecting against asthma and eczema: two allergic conditions whose incidence has soared in developed countries and seems oddly correlated with the degree to which the environment a child grows up in is spotlessly hygienic.

Previously: Joyride: Brief post-antibiotic sugar spike gives pathogens a lift, The future of probiotics and Researchers manipulate microbes in the gut
Photo by geraldbrazell

Evolution, Genetics, Obesity, Research, Science, Stanford News

Tiny fruit flies as powerful diabetes model

Tiny fruit flies as powerful diabetes model

Seung Kim

Fruit flies in your kitchen are unquestionably annoying. But the next time you’re trying to bat one out of the air around your too-ripe apples and bananas (or maybe that’s just me?), spare a few seconds to realize how important the tiny insects have been to science. They’ve been a darling of developmental biology for decades, as researchers identified genes (subsequently shown to be shared in mammals and humans) critically important in the metamorphosis from egg to animal. Frankly, it’s hard to over-estimate their contribution to science.

Now they’re set to take up a starring role in diabetes research. Stanford developmental biologist and Howard Hughes Medical Institute investigator Seung Kim, MD, PhD, and research associate Sangbin Park, PhD, have devised a way to measure insulin levels in fruit flies at the picomolar level – the level at which insulin concentrations are measured in humans. They’ve done so by successfully tagging the fruit fly insulin-like-peptide 2, or Ilp2, with a chemical tag. Their research was published today in PLOS Genetics.

From our release:

The experimental model is likely to transform the field of diabetes research by bringing the staggering power of fruit fly genetics, honed over 100 years of research, to bear on the devastating condition that affects millions of Americans. Until now, scientists wishing to study the effect of specific mutations on insulin had to rely on the laborious, lengthy and expensive genetic engineering of laboratory mice or other mammals.

In contrast, tiny, short-lived fruit flies can be bred in dizzying combinations by the tens of thousands in just days or weeks in small flasks on a laboratory bench.

In 2002, Kim and developmental biologist Roel Nusse, PhD, surprised many researchers when they showed that fruit flies develop a diabetes-like condition when their insulin-producing cells are destroyed. Further research has been stymied, however, by the difficulty of accurately measuring circulating insulin levels in the tiny animals. When speaking to me about the research, Kim called the new technique a “breakthrough” in the field.

Unlike many previous attempts by many groups, Park found two places in Ilp2 where the tag can be placed without affecting its biological activity. This allowed Kim and Park to track Ilp2 through its life cycle, as it’s produced by neurons in the brain (this is different from humans, who make insulin in beta cells in the pancreas), secreted into the blood stream and binds to insulin receptors in cells throughout the body. Parsing the effect of each mutation on the way the body produces, secretes and responds (or not) to insulin is critical to further understand the disease and to devise new therapeutic approaches. More from our release:

Park and his colleagues then turned their attention to mutations associated with type-2 diabetes in genome-wide studies in humans. These studies don’t reveal how a specific mutation might work to affect development of a disease; they show only that people with the condition are more likely than those without it to have certain mutations in their genome. Hundreds of candidate-susceptibility genes have been identified in this way.

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Evolution, Genetics, Global Health, Public Health, Research, Stanford News

Melting pot or mosaic? International collaboration studies genomic diversity in Mexico

Melting pot or mosaic? International collaboration studies genomic diversity in Mexico

6626429111_df791cbb8d_zMexico is a vast country with a storied past. Indigenous Native American groups across the country maintain their own languages and culture, while its cosmopolitan residents of large cities are as globally connected as anywhere on Earth. But Mexicans and Mexican Americans are usually lumped together as “Latinos” for the purposes of genetic or medical studies.

Now an international collaboration headed by Stanford geneticist Carlos Bustamante, PhD, and the University of California, San Francisco pulmonologist and public-health expert Esteban Burchard, MD, MPH, has assessed the breadth and depth of genomic diversity in Mexico for the first time. Their work was published today in Science. As I explain in our release:

The researchers compared variation in more than 1 million single nucleotide polymorphisms, or SNPs, among 511 people representing 20 indigenous populations from all over Mexico. They compared these findings with SNP variation among 500 people of mixed Mexican, European and African descent (a category called mestizos) from 10 Mexican states, a region of Guadalajara and Los Angeles, as well as with SNP variation among individuals from 16 European populations and the Yoruba people of West Africa.

The researchers found that Mexico’s indigenous populations diverge genetically along a diagonal northwest-to-southeast axis, with differences becoming more pronounced as the ethnic groups become more geographically distant from one another. In particular, the Seri people along the northern mainland coast of the Gulf of California and a Mayan people known as the Lacandon found near the country’s southern border with Guatemala are as genetically different from one another as Europeans are from Chinese.

Surprisingly, this pattern of diversity is mirrored in the genomes of Mexican individuals with mixed heritage (usually a combination of European, Native American and African):

Consistent with the history of the Spanish occupation and colonization of Mexico, the researchers found that the European portion of the mixed-individuals’ genomes broadly corresponded to that of modern-day inhabitants of the Iberian Peninsula. The Native American portion of their genomes, however, was more likely to correspond to that of local indigenous people. A person in the Mexican state of Sonora, for example, was likely to have ancestors from indigenous groups in the northern part of the country, whereas someone from Yucatan was more likely to have a southern native component in their genome, namely Mayan.

“We were really fascinated by these results because we had expected that 500 years of population movements, immigration and mixing would have swamped the signal of pre-Columbian population structure,” said Bustamante

Finally, the researchers found that the origin of the Native America portion of an individual’s genome affected a clinical measure of lung function abbreviated FEV1:

The researchers drew on data that calculated the predicted normal FEV1 for each subject based on age, gender, height and ethnicity (in this case, the reference was a standard used for all people of Mexican descent). To understand implications of these results within Mexico, they modeled the predicted lung function across Mexico, accounting for differences in local Native American ancestry for a large cohort of mestizos from eight states. The model predicts a marked difference across the country, with the average predicted FEV1 for a person from the northern state of Sonora and another from the state of Yucatan differing by about 7.3 percent. (That is, the population from Sonora has predicted values that were slightly higher than the average for the country, and those from the Yucatan were slightly lower.)

“There’s a definite predicted difference that’s due only to an individual’s Native American ancestry,” said Gignoux. “Variations in genetic composition clearly give a different physiological response.”

The researchers emphasize that a lower FEV1 does not necessarily mean a particular ethnic group has impaired lung function. Disease analysis takes place in the context of standardized values of matched populations, and the study points out how it is necessary to match people correctly to their ethnic backgrounds before making clinical decisions.

Stanford’s Andres Moreno Estrada, MD, PhD, and Christopher Gignoux, PhD, share first authorship of the study with Juan Carlos Fernandez Lopez, a researcher at Mexico’s National Institute of Genomic Medicine.

Previously: Roots of disease may vary with ancestry, according to Stanford geneticist, Recent shared ancestry between southern Europe and North Africa identified by Stanford researchers, and Caribbean genetic diversity explored by Stanford/University of Miami researchers
Photo by DL

Evolution, Genetics, Research, Science, Stanford News, Stem Cells

It’s a blond thing: Stanford researchers suss out molecular basis of hair color

It's a blond thing: Stanford researchers suss out molecular basis of hair color

blond hair, brighter

It’s all over the news today: Blonds aren’t stupid.

Well, that’s what most of the media would have you believe is the take-home message of the latest research by developmental biologist David Kingsley, PhD. And although I’m happy to see such great coverage, I’m hoping that readers realize that Kingley’s study on human hair color, which was published yesterday in Nature Genetics (subscription required), describes something much more subtle, and less superficial. From our release:

The study describes for the first time the molecular basis for one of our most noticeable traits. It also outlines how tiny DNA changes can reverberate through our genome in ways that may affect evolution, migration and even human history.

Kingsley, who is known for his study of a tiny fish called the threespine stickleback, is interested in learning how organism adapt to new environments by developing new traits. He’s found that this type of adaptation is most-often accomplished by changes in DNA regulatory regions that affect when, where and how a gene is expressed, rather than through (possibly disruptive) changes in the genes themselves.

In this case, he and his colleagues turned his attention to the blond hair common to many northern European and Icelanders. A previous study had shown that a single nucleotide change on human chromosome 12 was a major driver in hair color. As explained in the release:

The researchers found that the blond hair commonly seen in Northern Europeans is caused by a single change in the DNA that regulates the expression of a gene that encodes a protein called KITLG, also known as stem cell factor. This change affects how much KITLG is expressed in the hair follicles without changing how it’s expressed in the rest of the body. Introducing the change into normally brown-haired laboratory mice yields an animal with a decidedly lighter coat — not quite Norma Jeane to Marilyn Monroe, but significant nonetheless.

The involvement of KITLG, with its critical role in stem cell biology, is certainly interesting. But there’s also a more global lesson about the specificity of gene expression their effect on phenotype:

The study shows that even small, tissue-specific changes in the expression of genes can have noticeable morphological effects. It also emphasizes how difficult it can be to clearly connect specific DNA changes with particular clinical or phenotypic outcomes. In this case, the change is subtle: A single nucleotide called an adenine is replaced by another called a guanine on human chromosome 12. The change occurs over 350,000 nucleotides away from the KITLG gene and only alters the amount of gene expression about 20 percent — a relatively tiny blip on a biological scale more often assessed in terms of gene expression being 100 percent “on” or “off.”

“What we’re seeing is that this regulatory region exercises exquisite control over where, and how much, KITLG expression occurs,” said Kingsley. “In this case, it controls hair color. In another situation — perhaps under the influence of a different regulatory region — it probably controls stem cell division. Dialing up and down the expression of an essential growth factor in this manner could be a common mechanism that underlies many different traits.”

And now, the hook that excited most of the news media:

[Kingsley] added: “It’s clear that this hair color change is occurring through a regulatory mechanism that operates only in the hair. This isn’t something that also affects other traits, like intelligence or personality. The change that causes blond hair is, literally, only skin deep.”

Previously: Something fishy: Threespine stickleback genome published by Stanford researchers, Hey guys, sometimes less really is more , Tickled by stickle(backs) and Blond hair evolved more than once, and why it matters
Photo by Traci Lawson

Behavioral Science, Evolution, Medicine and Society, Ophthalmology, Research

Looks of fear and disgust help us to see threats, study shows

Looks of fear and disgust help us to see threats, study shows

disgustedNext time someone throws you a look, don’t take it personally: In a study of fear and disgust (the facial expressions), researchers have shown how those reactions to threat have helped us survive. Scientists studied the effects of eyes widening in fear, admitting more light and broading a participant’s field of vision, or narrowing in disgust, focusing more precisely on an object. As two-dozen undergraduate volunteers mimicked each emotion, scientists tracked their vision using using standard eye-exam equipment.

From a recent Los Angeles Times article:

Although some scientists have proposed that emotional expressions are intended primarily to communicate information, study authors argued that expressions of fear and disgust seem to perform different visual functions.

“Eye widening may improve detection and localization of a potential threat that requires enhanced vigilance, which would be consistent with the hypothesized function of fear,” wrote senior author Adam Anderson, [PhD,] a professor of human development at Cornell University. (The research was conducted by Anderson and his colleagues at the University of Toronto.)

“Conversely, eye narrowing may improve perceptual discrimination to discern different kinds of threats, such as disease vectors and contaminated foods, avoidance of which is a hypothesized function of disgust,” Anderson and his colleagues wrote.

The study was published in the journal Psychological Science.

Previously: Botox: frozen face = chilled emotional response? and Compassion, Darwin, facial expressions, the Dalai Lama – and counterterrorism?
Photo by Rachael Towne

Evolution, Immunology, Infectious Disease, Men's Health, Research, Stanford News

In men, a high testosterone count can mean a low immune response

In men, a high testosterone count can mean a low immune response

alpha maleMen have deeper voices and tons more facial and body hair than women. They are (usually) bigger, stronger, and much more likely to risk their lives on a whim. I, for example, have been known to bite a full-sized salami in half with a single snap of my jaws when hungry, angry or threatened. Or just for the hell of it.

But when it comes to immune response, men are wimps. It’s well documented that, for reasons that aren’t clear, men are more susceptible to bacterial, viral, fungal and parasitic infection than women are and that men’s immune systems don’t respond as strongly as women’s to vaccinations against influenza, yellow fever, measles, hepatitis and many other infectious diseases.

A new study just published in the Proceedings of the National Academy of Sciences by immunologist Mark Davis, PhD, who directs Stanford’s Institute for Immunity, Transplantation and Infection, and his colleagues may explain why. The same steroid hormone that makes a man’s beard, bones and muscles grow operates – albeit it in a slightly indirect way – to shrink immune responsiveness. Yep, we’re talking about (sigh…) that much-maligned male molecule, testosterone. In a nutshell, high circulating testosterone levels boost the activity of a clutch of genes that, among other things, dial down the aggressiveness with which our immune systems fight back against invading pathogens.

Now why, we ask ourselves, would evolution be so perverse as to have designed a hormone that on the one hand enhances classic male secondary sexual characteristics such as muscle strength, beard growth (or antler size, as the case may be) and risk-taking propensity – the very hallmarks of the alpha male – but on the other hand wussifies men’s immune systems?

Here’s what I got from talking at length (and, I admit, in an uncharacteristically high-pitched voice) to Davis in preparation for the news release I wrote about the study:

The evolutionary selection pressure for male characteristics ranging from peacocks’ plumage to deer’s antlers to fighter pilots’ heroism is pretty obvious: Females, especially at mating-cycle peaks, prefer males with prodigious testosterone-driven traits. Davis speculates that high testosterone may provide another, less obvious evolutionary advantage… Men are prone to suffer wounds from their competitive encounters, not to mention from their traditional roles in hunting, defending kin and hauling things around, increasing their infection risk. While it’s good to have a decent immune response to pathogens, an overreaction to them — as occurs in highly virulent influenza strains, SARS, dengue and many other diseases — can be more damaging than the pathogen itself. Women, with their robust immune responses, are twice as susceptible as men to death from the systemic inflammatory overdrive called sepsis. So perhaps, Davis suggests, having a somewhat weakened (but not too weak) immune system can prove more lifesaving than life-threatening for a dominant male in the prime of life.

Previously: Best thing since sliced bread? A (potential) new diagnostic for celiac disease, Deja Vu: Adults’ immune systems “remember” microscopic monsters they’ve seen before, Immunology escapes from the mouse trap and Immunology meets infotech
Photo by Craig Sunter *Click-64*

Evolution, Genetics, History, Myths, Research, Stanford News

New genetic study: More evidence for modern Ashkenazi Jews’ ancient Hebrew patrimony

New genetic study: More evidence for modern Ashkenazi Jews' ancient Hebrew patrimony

IsraelI hail from the so-called Ashkenazi branch of Jews, who account for the great majority of all Jews in the world today. Ashkenazis are distinguished by the historical fact that, over the last couple of thousand years or so, they propagated throughout Europe, generating and maintaining tens of thousands of distinctly Jewish communities in diverse countries spanning the entire continent. My dad was born in Lithuania; my mom’s mom came from an Eastern European region that has belonged to any one of about a half-dozen countries, depending on what particular year you happen to be talking about; and my mom’s dad grew up in Russia, near the Black Sea.

Tradition holds, though, that Ashkenazi Jews ultimately trace their origins straight back to ancient Israel, whence most Jews were expelled en masse in 70 CE by their Roman conquerors and sent skittering to all parts of the globe. (Jews who initially fled to Spain and Portugal are referred to as Sephardic. Those who took up residence in Iran, Turkey, Iraq and Northern Africa, are designated as Mizrahi.)

But in the late 1970s I read what was then a recent book titled The Thirteenth Tribe, written by polymath Arthur Koestler, advancing a theory that today’s Ashkenazis descend not from the Holy Land but, rather, from Khazaria, a medieval Turkic empire in the Causasus region whose royals, caught between the rock of Islam and the hard place of Christendom, chose the politically expedient course of converting to Judaism. That hypothesis has become highly politicized, with some groups holding that Ashkenazis, who constitute half of Israel’s current population, are colonialist interlopers with zero historical claim to the land of Israel.

Plausible at the time, the Khazar-origin premise has crumbled under the onslaught of modern molecular genetics. The latest volley: a study published this week in Nature Communications. The study’s senior author, Stanford geneticist Peter Underhill, PhD, works in the lab of  Carlos Bustamante, PhD, whose high-resolution techniques have highlighted the historical hopscotch of other migratory peoples.

Underhill, Bustamante and their co-authors analyzed the Y chromosome – a piece of the human genome invariably handed down father-to-son – of a set of Ashkenazi men claiming descent from Levi,  the founder of one of the Twelve Tribes of Israel. (Names such as Levy, Levine and Levitt, for example, bespeak a Levite heritage.)

If Ashkenazis were the spawn of Khazar royals, their DNA would show it. But those Y chromosomes were as Levantine as a levant sandwich. The same genetic “signature” popped up on every Levite sampled (as well as a significant number of non-Levite Ashkenazis), strongly implying descent from a single common ancestor who lived in the Fertile Crescent between 1,500 and 2,500 years ago. That signature is absent in the Y chromosomes of modern European non-Jewish men, and in male inhabitants of what was once Khazaria.

Yes, 2,000 years is a long time, and a fellow gets lonely. Genetic studies of mitochrondria – tiny intracellular power packs that have their own dollop of DNA and are always inherited matrilineally – have conflicted (contrast this with this) but, in combination with broader studies of entire genomes, suggest that a bit of canoodling transpired between Ashkenazi men and local European women, in particular Italian women, early in that two-millenia European sojourn.

I can relate. My wife is 100 percent Italian by heritage, and my daughter by my first marriage is half-Italian.

Previously: Caribbean genetic diversity explored by Stanford/University of Miami researchers, Stanford study investigates our most-recent common ancestors and Stanford study identifies molecular mechanism that triggers Parkinson’s
Photo by cod_gabriel

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