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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

Evolution, Genetics, History, Research, Science, Stanford News

On the hunt for ancient DNA, Stanford researchers improve the odds

On the hunt for ancient DNA, Stanford researchers improve the odds

110427-N-YY9999-002On the surface, it’s perfect Halloween fodder: Ancient Peruvian mummies, Bronze and Iron Age human teeth from Bulgaria and a thousands-of-years old hair sample from Denmark. In fact, one attendee of Stanford geneticist Carlos Bustamante’s talk this morning at the annual conference of the American Society of Human Genetics in Boston quipped that his introduction sounded like “the start of a joke.”

But really old human DNA (we’re talking thousands of years) holds amazing secrets about our distant past. What did we look like? Where did our ancestors come from? What diseases may we have had? Unfortunately, it’s much more difficult than it seems to unlock these mysteries.

Stanford postdoctoral scholar Meredith Carpenter, PhD, explained the problem in an e-mail to me yesterday:

From Neandertals to mammoths to Otzi the Iceman, discoveries in ancient DNA sequencing have been making headlines.  But what you might not realize is that most of the ancient genomes sequenced to date have come from exceptionally well-preserved specimens – Otzi, for example, was literally frozen in ice for 5000 years.

Ancient DNA specimens from temperate environments, in contrast, are much trickier to sequence because they contain high levels of environmental contamination, primarily derived from bacteria and other microbes inhabiting the ancient bone. This contamination often makes it too expensive to sequence the tiny amounts of endogenous DNA (which degrades over the years due to exposure to the elements) remaining in a sample.

Now, Carpenter and Bustamante, PhD, and their colleagues have hit upon a way to enrich, or increase the proportion of ancient human DNA in an environmental sample from about 1.2 percent to nearly 60 percent–rendering it vastly easier to sequence and analyze. They do so by exposing the sample to a genome-wide panel of human-specific RNA molecules to which the degraded DNA in the sample can bind. The effect is somewhat like stirring a pile of iron-rich dirt with a powerful magnet to isolate the metal from the soil.

This isn’t Bustamante’s first foray into the secrets of ancient DNA. Last year he published very interesting results showing that the ancestors of the famous Iceman likely came not from mainland Italy, as previously thought, but instead from the islands of Corsica or Sardinia. This new technique should enable researchers to learn even more about our ancestors, including those oh-so-intriguing mummies.

According to Carpenter:

We hope that this new method will enable ancient DNA researchers to more cheaply sequence a larger number of specimens, providing broader insight into historical populations rather than just a few well-preserved individuals.

The research is published online today in the American Journal of Human Genetics. If you’re interested in following tweets from the conference, which goes through tomorrow, you can do so by following hashtag #ASHG2013.

Previously: Iceman’s origins discovered at Stanford, Stanford study investigates our most-recent common ancestors  and Recent shared ancestry between Southern Europe and North Africa identified by Stanford researchers.
Photo by Official US Navy Imagery

Evolution, In the News, Science

419 million year-old fish fossil may reveal origins of the human jaw

6971051776_9c4c9a71a6_nAs a kid, I used to ponder the origins of my unusually square jawline while looking in the bathroom mirror. After reading this story in Nature News, I wonder if I should have pondered my jaw’s origins while walking the halls of the nearest aquarium instead. Researchers from the Chinese Academy of Sciences in Beijing discovered a well-preserved 419 million year-old fossil that suggests the armor-plated fish, called Entelognathus primordialis, may be the earliest known species with a jaw like ours.

From Nature News:

Entelognathus primordialis is a new addition to the placoderms, a class of armour-plated fishes that lived from about 430 million to 360 million years ago. Like most vertebrates, including mammals, placoderms had a bony skull and jaw, but most of them had simple beak-like jaws built out of bone plates.

If you’re stifling a yawn, consider this: Researchers have seen fossils of this fish species before, but they were in less than pristine shape. Based on these fossils, most scientists concluded that this species was unrelated to humans.

Now, the discovery of this well-preserved fossil described in the journal Nature by paleontologist Min Zhu, PhD, and his team may upend this view of our family tree. Eliot Barford of Nature News explains:

There is a serious possibility that the modern bony visage originated with E. primordialis’s ancestors. This would mean that humans look more like the last common ancestor of living jawed vertebrates than we thought, and that sharks are less primitive than palaeontologists assumed, having done away with their bones as an adaptation.

However, the rearranged family tree is not yet quite conclusive, write the authors of a related News & Views article. There remains a chance that E. primordialis evolved its jaw independently from the bony fish, so that we did not inherit it, and the resemblance is an illusion.

Holly MacCormick is a writing intern in the medical school’s Office of Communication & Public Affairs. She is a graduate student in ecology and evolutionary biology at University of California-Santa Cruz.

Previously: Stanford study investigates our most-recent common ancestorsRecent shared ancestry between Southern Europe and North Africa identified by Stanford researchers and Stanford engineer studies bones that aid hearing
Photo by cuatrok77

Evolution, otolaryngology, Research, Stanford News

Stanford engineer studies bones that aid hearing

Stanford engineer studies bones that aid hearing

What distinguishes us from the dinosaurs? Three middle ear bones, for starters. Stanford mechanical engineer Sunil Puria, PhD, studies inner- and middle-ear biomechanics and the role of bone conduction in hearing, and he’s among a number of scientists who are curious why we have the tiny malleus, incus and stapes but reptiles and birds don’t.

Read more from Stanford Report on what Puria’s research on bone conduction hearing could mean for treating hearing loss, enhancing sound technology, and understanding evolutionary biology.

Previously: Battling hearing loss on and off the battlefield and Hearing loss patient discusses why Stanford research gives her hope for an eventual cure

Evolution, Genetics, Research, Stanford News

Stanford study investigates our most-recent common ancestors

Stanford study investigates our most-recent common ancestors

skullsGenealogy buffs know the thrill that comes with identifying ancestors further and further up the family tree. Reaching back through the sands of time to learn when, where and how our relatives lived is like a very personal treasure hunt.

Now geneticist Carlos Bustamante, PhD, and his colleagues have done something similar for our Y-chromosomal “Adam” and mitochondrial “Eve”: two individuals who have passed down a portion of their genomes to the vast expanse of humanity. These people are known as our most-recent common ancestors, or MRCAs. From our release:

“Previous research has indicated that the male MRCA lived much more recently than the female MRCA,” said Bustamante… “But now our research shows that there’s no discrepancy.” Previous estimates for the male MRCA ranged from between 50,000 to 115,000 years ago.

Bustamante’s research indicates the two MRCAs roughly overlapped during evolutionary time: from between 120,000 to 156,000 years ago for the man, and between 99,000 and 148,000 years ago for the woman. More from the release :

Despite the Adam and Eve monikers, which evoke a single couple whose children peopled the world, it is extremely unlikely that the male and female MRCAs were exact contemporaries. And they weren’t the only man and woman alive at the time, or the only people to have present-day descendants. These two individuals simply had the good fortune of successfully passing on specific portions of their DNA, called the Y chromosome and the mitochondrial genome, through the millennia to most of us, while the corresponding sequences of others have largely died out due to natural selection or a random process called genetic drift.

The researchers used high-throughput sequencing technology to sequence the Y chromosomes of 69 men from nine globally distinct regions. They identified about 11,000 differences among the sequences, which allowed them to determine phylogentic relationships and timelines with unprecedented accuracy. As graduate student and study co-author David Poznik described:

Essentially, we’ve constructed a family tree for the Y chromosome. Prior to high-throughput sequencing, the tree was based on just a few hundred variants. Although these variants had revealed the main topology, we couldn’t say much about the length of any branch — the number of variants shared by all of its descendants. We now have a more complete structure, including meaningful branch lengths, which are proxies for the periods of time between specific branching events.

Previously: Recent shared ancestry between Southern Europe and North Africa identified by Stanford researchers, Cracking the code of 1000 (make that 1092!) genomes and Blond hair evolved more than once-and why it matters
Photo by tup wanders

Evolution, Research, Stanford News

Mammals can “choose” the sex of their offspring, Stanford study finds

Mammals can "choose" the sex of their offspring, Stanford study finds

monkey and mama

A Stanford researcher and his colleagues have produced a surprising new study which shows that mammals can effectively “choose” the sex of their offspring and they’re doing it for their own selfish reasons – so they can have more grandchildren.

The researchers used data on more than 2,300 animals at the San Diego Zoo to track three generations for nearly 200 mammal species. Their numbers confirm what evolutionary biologists have theorized for decades – that females are strategically evaluating their options and making decisions that will serve their own reproductive interests, said Joseph Garner, PhD, associate professor of comparative medicine at Stanford and senior author of the study. Garner told me:

You can think of this as being girl power at work in the animal kingdom. We like to think of reproduction as being all about the males competing for females, females dutifully picking the winner. But in reality females have much more invested than males, and they are making highly strategic decisions about their reproduction based on the environment, their condition, and the quality of their mate. Amazingly, the female is somehow picking the sperm that will produce the sex that will serve her interests the most: the sperm are really just pawns in a game that plays out over generations.

What the researchers found is that grandparents could strategically choose to give birth to sons, if the sons would be of high enough quality to give them more grandchildren. In fact, they found that when females did have mostly sons, those sons had 2.7 times more children per capita than those who had equal numbers of male and female offspring. The same was true for male grandparents, with the study showing that when grandfathers produced mostly sons, those sons on average had 2.4 times more children per capita. But again, it’s most likely the females controlling the process, Garner said.

How they do it remains a bit of a mystery, he said, though one theory is that females control the sperm as it moves through the reproductive tract, selectively slowing down or speeding up the sperm they want to select.

Garner noted that there have been studies showing some similar patterns among humans. For instance, one found that billionaires are more likely to have sons than daughters because sons tend to retain the family’s wealth, or so the theory goes.

To read more on this tantalizing subject, see the study, which appears online today in PLOS ONE.

Photo by EvaSwensen

Evolution, Genetics, Immunology, In the News, Infectious Disease, Research

All in the family: Uncovering the genetic history of the world’s most lethal pathogens

All in the family: Uncovering the genetic history of the world's most lethal pathogens
They’re tiny terrors that are best known for the millions of people they’ve killed. Few us of would want to meet them, or their relatives. But for researchers like Verena J. Schuenemann, PhD, and Johannes Krause, PhD, uncovering the pedigrees of the world’s most lethal pathogens is an important step in combating the diseases we avoid like the plague.

Earlier this week in Forbes, writer John Farrell told the tale of the two scientists from the University of Tübingen in Germany, and how they hunt down some of the most notorious pathogens in history.

Studies such as work done by Schuenemann, Krause, and a team of international researchers on potato blight, the Black Death, and (most recently) leprosy, are changing our understanding of diseases that were once buried in the past. As Ann Gibbons of Science recently wrote (subscription required):

Awash in data, several labs are racing neck-and-neck to cull DNA from a Most Wanted list of legendary killers: tuberculosis (TB), plague, cholera, Leishmania, leprosy, the potato blight, and AIDS. They gather traces of these culprits from ancient teeth, bones, hair, feces, and—in the case of potato blight—from skin and leaves, then unleash the sequencers. The work, which began in earnest 3 years ago, adds a new dimension to our understanding of historical events, revealing the true nature of the villains responsible for humanity’s worst epidemics. “There are a lot of diseases described in the historical record that we don’t know what the pathogen is,” says molecular anthropologist Anne Stone of Arizona State University, Tempe.

One persistent question is how the deadliest pathogens evolve over time. As Farrell outlines in his piece, Schuenemann’s team found that the bacteria (Yersinia pestis) responsible for plagues in Africa today are genetically similar to the bacteria that unleashed the Black Death on Europeans in 1347. But, today’s plagues are less lethal – which suggests that evolution knocked a few teeth out of Black Death’s lethal bite.

Understanding when and how evolution changes a pathogen’s virulence is important because the plague is a re-emerging disease and history could repeat itself.

Holly MacCormick is a writing intern in the medical school’s Office of Communication & Public Affairs. She is a graduate student in ecology and evolutionary biology at University of California-Santa Cruz.

Previously: A journalist’s experience with tuberculosis, the “greatest infectious killer in human history”, Image of the Week: Leprosy bacteria and interferon-beta and Tropical disease treatments need more randomized, controlled trials, say Stanford researchers
Image, of the skull of a 25-year-old woman with leprosy, from Ben Krause-Kyora, PhD, with Kiel University. The genetic material extracted from the skeleton enabled the decoding of the genome of the leprosy pathogen.

Behavioral Science, Evolution, Neuroscience, Research, Stanford News

We’ve got your number: Exact spot in brain where numeral recognition takes place revealed

We've got your number: Exact spot in brain where numeral recognition takes place revealed

Your brain and my brain are shaped slightly differently. But, it’s a good bet, in almost the identical spot within each of them sits a clump of perhaps 1 to 2 million nerve cells that gets much more excited at the sight of numerals (“5,” for example) than when we see their spelled-out equivalents (“five”), lookalike letters (“5″ versus “S”) or scrambled symbols composed of rearranged components of the numerals themselves.

Josef Parvizi, MD, PhD, director of Stanford’s Human Intracranial Cognitive Electrophysiology Program, and his colleagues identified this numeral-recognition module by recording electrical activity directly from the brain surfaces of epileptic volunteers. Their study describing these experiments was just published in The Journal of Neuroscience.

As I explained in my release about the work:

[A]s a first step toward possible surgery to relieve unremitting seizures that weren’t responding to therapeutic drugs, [the patients had] had a small section of their skulls removed and electrodes applied directly to the brain’s surface. The procedure, which doesn’t destroy any brain tissue or disrupt the brain’s function, had been undertaken so that the patients could be monitored for several days to help attending neurologists find the exact location of their seizures’ origination points. While these patients are bedridden in the hospital for as much as a week of such monitoring, they are fully conscious, in no pain and, frankly, a bit bored.

Seven patients, in whom electrodes happened to be positioned near the area Parvizi’s team wanted to explore, gave the researchers permission to perform about an hour’s worth of tests. In the first, they watched a laptop screen on which appeared a rapid-fire random series of letters or numerals, scrambled versions of them, or foreign number symbols with which the experimental subjects were unfamiliar. In a second test, the experimental subjects viewed, again in thoroughly mixed-up sequence, numerals along with words for them as well as words that sounded the same (1″, “one”, “won”, “2″, “two”, “too”, etc.).

A region within a part of the brain called the inferior temporal gyrus showed activity in response to all kinds of squiggly lines, angles and curves. But within that area a small spot measuring about one-fifth of an inch across lit up preferentially in response to numerals compared with all the other stimuli.

The fact that this spot is embedded in a larger brain area generally responsive to lines, angles, and curves testifies to the human brain’s “plasticity:” its ability to tailor its form and function according to the dictates of experience.

“Humans aren’t born with the ability to recognize numbers,” says Parvizi. He thinks evolution may have generated, in the brains of our tree-dwelling primate ancestors, a brain region particularly adept at computing lines, angles and curves, facilitating snap decisions required for swinging quickly from one branch to the next.

Apparently, one particular spot within that larger tree-branch-interesection recognition area is easily diverted to the numeral-recognition activity constantly rewarded by parents and teachers during the numeracy boot camp called childhood.

Nobody can say those little monkeys don’t learn anything in kindergarten.

Previously: Metamorphosis: At the push of a button, a familiar face becomes a strange one and Why memory and math don’t mix: They require opposing states of the same brain circuitry
Photo by qthomasbower

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