Wednesday, 21 October 2009

Johnald's Fantastical Daily Link Splurge

Johnald's Fantastical Daily Link Splurge

Out of LSD? Just 15 Minutes of Sensory Deprivation Triggers Hallucinations

Posted: 21 Oct 2009 11:28 AM PDT


You don't need psychedelic drugs to start seeing colors and objects that aren't really there. Just 15 minutes of near-total sensory deprivation can bring on hallucinations in many otherwise sane individuals.

Psychologists stuck 19 healthy volunteers into a sensory-deprivation room, completely devoid of light and sound, for 15 minutes. Without the normal barrage of sensory information flooding their brains, many people reported experiencing visual hallucinations, paranoia and depressed mood.

"This is a pretty robust finding," wrote psychiatrist Paul Fletcher of the University of Cambridge, who studies psychosis but was not involved in the study. "It appears that, when confronted by lack of sensory patterns in our environment, we have a natural tendency to superimpose our own patterns."

The findings support the hypothesis that hallucinations happen when the brain misidentifies the source of what it is experiencing, a concept the researchers call "faulty source monitoring."

"This is the idea that hallucinations come about because we misidentify the source of our own thoughts," psychologist Oliver Mason of the University College London wrote in an email to "So basically something that actually is initiated within us gets mis-identified as from the outside." Mason and colleagues published their study in October in the Journal of Nervous and Mental Disease.

To choose people for their study, the researchers asked more than 200 volunteers to complete a questionnaire called the "Revised Hallucinations Scale," which measures the predisposition of healthy people to see things that aren't really there. The scientists picked participants who scored in either the upper or lower 20th percentile, so they could compare how short-term sensory deprivation affects a range of individuals.

Study participants sat in a padded chair in the middle of an anechoic chamber, a room designed to dampen all sound and block out light. The researchers describe the set-up as a "room within a room," with thick outer walls and an inner chamber formed by metallic acoustic panels and a floating floor. In between the outer and inner walls are large fiberglass wedges. "This results in a very low noise environment in which the sound pressure due to outside levels is below the threshold of hearing," the researchers wrote.

Though participants had a panic button, none of them used it. After spending 15 minutes deprived of sight and sound, each person completed a test called the "Psychotomimetic States Inventory," which measures psychosis-like experiences and was originally developed to study recreational drug users.

Among the nine participants who scored high on the first survey, five reported having hallucinations of faces during the sensory deprivation, and six reported seeing other objects or shapes that weren't there. Four also noted an unusually heightened sense of smell, and two sensed an "evil presence" in the room. Almost all reported that they had "experienced something very special or important" during the experiment.

As expected, volunteers who were less prone to hallucinations experienced fewer perceptual distortions, but they still reported a variety of delusions and hallucinations.

The researchers were not altogether surprised by such dramatic results from only 15 minutes of sensory deprivation. Although few scientists are studying sensory deprivation today, a small body of research from the 1950s and 1960s supports the idea that a lack of sensory input can lead to symptoms of psychosis.

"Sensory deprivation is a naturalistic analogue to drugs like ketamine and cannabis for acting as a psychosis-inducing context," Mason wrote, "particularly for those prone to psychosis."

We still don't know why some people are more likely to have hallucinations than others, but Fletcher says that some researchers consider the phenomenon particularly important because it suggests that symptoms of mental illness occur on a continuum with normality.

"Perhaps this reflects different ways of dealing with sense data, which under certain circumstances might be advantageous," Fletcher wrote.

Next, the researchers hope to study how sensory deprivation affects schizophrenic patients and people who use recreational drugs that increase the risk of psychosis.

"There are claims that schizophrenic patients paradoxically find that their psychotic symptoms such as hearing voices are improved by sensory deprivation," Mason wrote, "though the evidence for this is very long in the tooth indeed. What happens to people who already hear voices when in the chamber?"

Via MindHacks.

Image: Flickr/daveknapik

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Obama Win Turned Male Republicans Into Girlie Men

Posted: 21 Oct 2009 10:44 AM PDT


Those who remember the street parties of Election Night 2008 might think the testosterone levels of Obama voters had shot up in triumph. That would be wrong.

Instead, liberal testosterone levels stayed stable, while those of male Republican voters plummeted. The latter also reported feeling submissive and unhappy.

There are many ways to read these results, which are based on saliva samples taken from 183 men and women as the polls closed, and again when President Obama's victory was officially announced.

First, male voters get the same vicarious boost from a candidate's political victory as they would their favorite sports team beating a rival. That's the main academic finding of the study, published Wednesday in Public Library of Science ONE, but one that seems rather self-evident.

election_testosteroneMuch more interesting is the split. Obama voter testosterone merely stabilized. The researchers suggest that, as nighttime testosterone levels typically dip, stabilization "is conceptually similar to a rise."

But if testosterone usually just dips at night, it positively plummeted for Republican men.

Indeed, Republican men "felt significantly more controlled, submissive, unhappy, and unpleasant at the moment of the outcome" than those who voted for Obama, the researchers wrote. "Moreover, since the dominance hierarchy shift following a presidential election is stable for 4 years, the stress of having one's political party lose control of executive policy decisions could plausibly lead to continued testosterone suppression in males."

Women of both political parties, it should be noted, experienced no significant testosterone changes on election night.

Image: Flickr/Mborowick

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Citation: "Dominance, Politics, and Physiology: Voters' Testosterone Changes on the Night of the 2008 United States Presidential Election." By Steven J. Stanton, Jacinta C. Beehner, Ekjyot K. Saini, Cynthia M. Kuhn, Kevin S. LaBar. PLoS ONE, October 21, 2009.

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Bone Crunching Debunks ‘First Monkey’ Ida Fossil Hype

Posted: 21 Oct 2009 10:42 AM PDT


Originally promoted as the stem of the primate family tree, it now appears that Darwinius masillae — better known as "Ida," the fossil that "changes everything" — belonged to a fringe branch.

This is the conclusion of researchers who analyzed primate fossils to determine where their own discovery, dubbed Afradapis and closely related to Darwinius, belongs on the tree. Far from spawning the ancestors of humans, the 47 million-year-old Darwinius seems merely to have gone extinct, leaving no descendants.

"It's the first phylogenetic analysis of this important animal," said study co-author Jonathan Perry, a Midwestern University paleoanthropologist. "By our analysis, the taxon Darwinius does not appear to be" at the root of all simians, said Perry. "It's on the opposite side of the tree."

The analysis of Perry's team, published Wednesday in Nature, would likely be of purely academic interest had Darwinius been introduced according to paleontological custom. That would have been in carefully written papers presented for review to the scientific community, who already had some informal familiarity with the research. But that's precisely what didn't happen.

Known from a single specimen purchased by the University of Oslo from a private fossil collector and studied in total secrecy, Darwinius was announced to the world at a May press conference featuring New York City mayor Michael Bloomberg. The scientific article describing Darwinius, published in PLoS ONE, came after the TV special and book, both entitled The Link.

"This is the first link to all humans," said Jørn Hurum, a member of the Darwinius team, at the press conference. His colleague Jens Franzen likened its scientific impact to "an asteroid falling down to Earth." Hurum said the fossil, named "Ida" in honor of his daughter, would be a paleontological "Mona Lisa for the next 100 years." Ida was front-page news; Google celebrated it with an iconic logo cartoon. The only people unimpressed by their conclusions were scientists.

As prominent paleontologists soon pointed out, Hurum's team was pushing a theory that most researchers had already dismissed, that anthropoids — monkeys and apes, including ourselves — are descended from lemur-like members of a primate subfamily called adapids, of which Darwinius was one.

According to Hurum's team, Darwinius possessed many of the physical traits expected in the earliest ancestral anthropoid, so it must be that ancestor. And since Darwinius was clearly an adapid, then adapids were at the root of the anthropoids. But their paper made no reference to extensive fossil and genetic evidence suggesting otherwise.

At the time, asked by The New York Times about his team's promotion, Hurum said that "any pop band is doing the same thing," and that "we have to start thinking the same way in science." Contacted by e-mail about the Nature study, he said, "At last the scientific discussion starts!"

adapiform_treeThe Nature paper marks the debut of another adapiform, called Afradapis and known from a handful of fossil teeth and jawbone fragments gathered over the last several years in Egypt.

To better understand Afradapis' place in the primate narrative, Perry's team studied fossil measurements gathered from 117 living and extinct primate species. In what's known as a cladistic analysis, they ran the measurements through a computer program that determined the most likely evolutionary configuration of the species.

No such analysis was performed by Hurum's team on Darwinius. And according to Perry's cladistics, both Darwinius and Afradapis are located where conventional wisdom expected them to be — on an early twig of the branch that produced lemurs, and far from the lineage that spawned monkeys and great apes.

The study "is spot-on in its interpretation of the phylogenetic position of Darwinius," said Richard Kay, a Duke University evolutionary anthropologist whose review of The Link was entitled, "Much Hype and Many Errors."

Christopher Beard, a Carnegie Museum of Natural History paleontologist who originally called Darwinius "a third cousin twice removed," also agreed with the Nature results. Darwinius "is only very distantly related to living and fossil anthropoids," said Beard.

Hurum retorted that "there's a lot of ways to do cladistics," and said the Nature authors used only some of their Darwinius measurements, ostensibly omitting those that might have provided a different evolutionary narrative.

Philip Gingerich, a University of Michigan paleontologist and member of the Darwinius team, said the Nature team's explanation of Afradapis was "implausible," given how much it looks like a monkey — and Darwinius looks even more monkey-like.

This back-and-forth is typical of science and especially paleoanthropology, a research field predicated on competing interpretations of tiny bone fragments. It's also the sort of dialogue that was missing from Darwinius' overhyped debut.

"Ultimately it's about science, and how sound the science is," said Perry.

Images: 1. Darwinius masillae, from PLoS ONE. 2. The adapiform branch of the primate family tree, from Nature. D. masillae is highlighted, and located beside Afradapis; the great apes, including humans, trace their origins to the stem and crown Anthropoidea.

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Citation: "Convergent evolution of anthropoid-like adaptations in Eocene adapiform primates." By Erik R. Seiffert, Jonathan M. G. Perry, Elwyn L. Simons & Doug M. Boyer. Nature, Vol. 461 No. 7267, October 22, 2009.

Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecosystem and planetary tipping points.

Even-More-Gigantic Giant Orb Spider Discovered

Posted: 20 Oct 2009 05:00 PM PDT


Scientists have found the world's largest species of golden orb-weaver spider in the tropics of Africa and Madagascar. The discovery marks the first identification of a new Nephila spider since 1879.

Females of the new species, Nephila komaci, measure a whopping 4 to 5 inches in diameter, while the male spiders stay petite at less than a quarter of their mate's size. So far, only a handful of these enormous arachnids have been found in the world.

"We fear the species might be endangered, as its only definite habitat is a sand forest in Tembe Elephant Park in KwaZulu-Natal," ecologist Jonathan Coddington of the Smithsonian's National Museum of Natural History said in a press release. "Our data suggest that the species is not abundant, its range is restricted, and all known localities lie within two endangered biodiversity hotspots: Maputaland and Madagascar."


The first potential specimen of the new species was uncovered by Coddington and his colleague Matjaz Kuntner of the Slovenian Academy of Sciences and Arts in 2000. They found a huge female orb-weaver among a museum collection of spiders in Pretoria, South Africa, and she didn't match the description of any known spider. Although they hoped the unusual-looking giant represented a new species, several dedicated expeditions to South Africa failed to find any live spiders of a similar description.

Then, in 2003, a second specimen from Madagascar was found at a museum in Austria, suggesting that the first spider hadn't been a fluke. But despite a comprehensive search through more than 2,500 samples from 37 museums, no additional specimens turned up, and the researchers assumed the biggest of all orb-weavers was probably extinct.

Finally, three live spiders have been found to prove the scientists wrong: A South African researcher found two giant females and one male in Tembe Elephant Park, proving that the new species was not extinct, just incredibly rare.

"Only three have been found in the past decade," Kuntner wrote in an e-mail to "None by our team, despite focused searches. Only an additional two exist in old museum collections. Compared to thousands of exemplars of other Nephila species in museums, that is disproportionately rare."

The two biologists named the new species after Andrej Komac, a scientist friend of Kuntner's who died in an accident near the time of the discoveries.

Like all Nephila spiders, females of the new species spin huge webs of golden silk, often more than 3 feet in diameter. In the report of the discovery of this rare spider, published Tuesday in PLoS One, the researchers also addressed the evolution of the dramatic size difference between male and female orb-weavers.

By mapping out the evolutionary tree of all known orb-weaver species, the scientists discovered that as the spiders evolved, females got bigger and bigger, while males stayed roughly the same size.

"It is good for females to be big, because they can lay so many more eggs," Coddington wrote in an e-mail. In addition, large size probably helps females avoid being eaten by predators.

"Relatively few groups can safely pluck an orb-weaving spider from its web," he wrote, "because you have to be able to hover to do so (hummingbirds, wasps, damselflies come to mind). None of these are large enough to tackle an adult Nephila, or even a large juvenile."

Males, on the other hand, are better off staying small and reaching sexual maturity at a young age. Because males spend most of their time underground, hunting for a mate is one of the most dangerous activities they undertake.

"So males risk everything to find, probably, just one, huge female, inseminate her, and probably do not willingly leave her web to search for another," Coddington wrote. "Nothing about sex says males must be big."

Image 1: Tiny male Nephila spiders are dwarfed by their female counterparts. Matjaz Kuntner and Jonathan Coddington/PLoS ONE.
Image 2: A giant golden orb-web exceeding 1 meter in diameter, spun by a
Nephila inaurata spider. M Kuntner.

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Life Ingredients Found on Extrasolar Gas Giant

Posted: 20 Oct 2009 01:31 PM PDT

Hot, Dry and Cloudy Planet

The basic ingredients for life have been found around a second extrasolar planet, scientists reported Tuesday.

Although the planet itself is not habitable by life as we know it, the discovery could mean that the basic components of life are widespread in the atmospheres of many kinds of exoplanets.

The new find was made by training both the Hubble and Spitzer Space Telescopes on HD 209458b, a hot Jupiter that orbits very close to its sunlike star. It's located 150 light years away in the Pegasus constellation. In December of last year, Jet Propulsion Laboratory astronomer Mark Swain and his team found a similar Jupiter-like planet, HD 189733b, with carbon dioxide in its atmosphere.

"Detecting organic compounds in two exoplanets now raises the possibility that it will become commonplace to find planets with molecules that may be tied to life," Swain said in a press release.

The study of exoplanets has exploded since the first were discovered in the early 1990s. Just Monday, astronomers announced the discovery of 32 new exoplanets. And detections aren't just growing in number, but sophistication as well. Exoplanetary scientists are learning more and more about the systems in which the planets are found.

Early exoplanet discoveries were made using a variety of techniques, but primarily by measuring the "wobble" a star exhibits in the presence of another massive body. In more recent years, scientists have looked for "transiting" planets, which pass in front of and behind their stars. Far more can be learned about these celestial bodies.

When an exoplanet passes in front of its star, scientists are able to translate small differences in the color of the light arriving at Earth into a chemical signature for the planet's atmosphere. For example, HD 209458b has water and carbon dioxide, just like HD 189733b, but it's also got a lot more methane.

"The high methane abundance is telling us something," said Swain. "It could mean there was something special about the formation of this planet."

Planetary spectroscopy is easiest to do for systems in which a large exoplanet orbits very close to its home star. With smaller planets orbiting farther from their star, it is harder to detect the minute changes in the star's light.

Though the Kepler Space Telescope is likely to find many Earth-like planets, it could be a decade before we have the technological capability to definitively detect a rocky planet with an atmosphere and orbit like ours, an Earth twin.

Rendering: NASA/JPL-Caltech/T. Pyle (SSC)

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Human Brain Can Control Single Celebrity-Recognizing Neurons

Posted: 20 Oct 2009 11:32 AM PDT


CHICAGO — The Halle Berry fan club is expanding one brain cell at a time. By eavesdropping on the activity of single neurons in the human brain, scientists have figured out which brain cells go wild for superstars such as the popular actress. And the newest research shows that people can activate those cells selectively.

sciencenews"This study is the first demonstration of humans' ability to control the activity of single neurons," the researchers wrote in a summary of their study. The results, presented October 19 at the Society for Neuroscience's annual meeting by Moran Cerf of the California Institute of Technology in Pasadena, may help researchers understand how each cell in the brain sees and responds to the world.

"This type of work gives us some clues about what's going on in the brain," comments Christoph Weidemann of the University of Pennsylvania, who studies how the brain processes information. "It's quite an amazing feat for the brain to make sense of its input and reliably recognize people and objects."

The new study was conducted on people with epilepsy. Doctors had implanted electrodes in these patients' brains to track where seizures originate. The researchers used these same electrodes to eavesdrop on the activity of single brain cells in a part of the brain called the medial temporal lobe, which is important for "memory, attention, perception — the things that we care about the most," Cerf said in his presentation.

Before the experiment began, Cerf and his colleagues showed volunteers familiar images of people, objects or places, chosen on the basis of extensive interviews about the patients' preferences. Pictures included images of Bill Clinton, Michael Jackson and Venus Williams, among others. "We hoped to locate neurons in their brains that respond selectively to one of those concepts," Cerf said in his talk.

In each patient, the researchers found about five neurons that fired when the patient looked at an image of a certain person or object. A person might have, for example, a Halle Barry neuron, a Marilyn Monroe neuron, an Eiffel tower neuron, a Michael Jackson neuron and a spider neuron.

Once these neurons were identified, the researchers wanted to know if the patients could control them by thinking about that certain person or object. To do this, Cerf and his colleagues hooked up the neuron-sensing electrodes to a computer that then displayed images representative of the person's thought. When a patient's Marilyn Monroe neuron became active, the screen would show an image of Marilyn Monroe.

To see how well the patients could control these single neurons, researchers set up what they call the "fade" experiment, which is like a competition between two different neurons. One version of the experiment involved a neuron that responded to Goonies' star Josh Brolin and another neuron that responded to Marilyn Monroe. Initially, the person was shown a hybrid image of these two stars overlaid on each other. When the person was told to think of Josh Brolin, the electrodes would record that neuron's activity and send the data to the computer, causing the Monroe image to fade and the Brolin image to get brighter. The experiment was finished when the picture was completely Brolin or Monroe, or 10 seconds had elapsed. Ten patients underwent this test and successfully directed the pictures between 60 and 90 percent of the time, the researchers found. As the testing went on, the patients became better at controlling the neurons.

Scientists are still far from being able to see people's innermost thoughts, Weidemann says. "When people talk about mind reading, there's a tendency to think of 1984 and all the negative aspects of it," he says. "The goal here is to understand cognitive processes."

A better understanding of how the brain encodes information may be useful for building machines that can be controlled directly from people's brains. Such devices may ultimately help people who are unable to communicate.

Images: AP, Monroe: Matty Zimmerman, Brolin: Chris Pizzello (these are not the images used in the study)

2005 discovery of the "Halle Berry" neuron

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NASA Test Rocket Rides to Launch Aboard Apollo-Era Crawler

Posted: 20 Oct 2009 10:58 AM PDT


The first test flight for NASA's next-generation rocket rumbled closer when the Ares I-X rocket took a ride to its launch spot aboard a massive Apollo-era crawler Tuesday morning.

The test rocket, which incorporates most of the core components of the Ares I, which will actually be used for missions in the future, reached Launch Pad 39B at Kennedy Space Center at 9:17 a.m. Eastern after a 4.2 mile trip that took nearly eight hours.

The Ares I-X test rocket has more than 700 sensors that will allow NASA to ground-truth some of its calculations about the safety and performance of the rocket. Some critics have argued that the Ares I-X is too different from the real Ares I, though, to provide meaningful data. The Ares I-X is powered by a four-segment solid rocket booster, while the real deal will have five.

The Ares I-X is scheduled to launch October 27th, and NASA officials hailed its arrival at the launch pad as a major milestone for the Constellation program, which was former NASA administrator Michael Griffin's plan to execute President George W. Bush's Vision for Space Exploration. Bush laid out an ambitious plan to return to the moon and then continue on to Mars. NASA's funding levels, though, never matched the grand scheme.

Constellation and the ideas that inspired it have come under heavy criticism over the last five years. Some have questioned technical decisions made by Michael Griffin and the chief architect of the Ares rocket, Scott "Doc" Horowitz, who left the agency in 2007. Commercial space companies like SpaceX and Bigelow Aerospace have argued for a larger role for private industry in providing human launch services to low-earth orbit. And some scientists, especially, have wondered why we're sending humans to space at all.

In an effort to address at least some of these concerns, President Obama asked for a special, independent panel to review NASA's plans for human spaceflight. Chaired by Norm Augustine, former CEO of Lockheed Martin, that commission will release its final report on Thursday.

In a preliminary summary report, the Augustine panel made it clear that NASA does not have enough money to carry out a human spaceflight program and its other science programs. They presented a series of alternatives to Constellation that would send humans to different destinations and use different rockets.

Their original report came under withering attacks when it was presented in the House, but its ultimate audience is President Obama and the head of the Office for Science and Technology Policy, John Holdren. Rumors abound that they might be cooking up major changes to Constellation.

While NASA employees wait to hear if their agency will get a new direction, they've soldiered on with the Constellation program, assembling and preparing to test the Ares I-X rocket. In trying to return to the moon, NASA has often echoed Apollo, the most popular space program ever. In this case, the Ares I-X took a ride on one of two crawlers built to carry around the Saturn V rockets that sent astronauts to the moon.

When they were first completed in 1966, they were technical marvels — and they remain so today. Weighing in at 5.5 million pounds each, the vehicles' carrying decks are large enough to fit a baseball diamond. The crawlers are powered by twin 2,750 horsepower diesel engines and sit atop enormous tank-like treads.

They've been kept running by a crack team at Kennedy Space Center, allowing the old machines to keep on trucking all the way through the Space Shuttle-era. These relics from Apollo are a reminder that while many things have changed at the agency, some haven't had to.


Images: NASA. 1. The Ares I-X nearly in place. 2. A crawler-transporter carrying a Saturn V rocket into place.

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Fossils Push Back Earliest Complex Animals 40 Million Years

Posted: 20 Oct 2009 09:32 AM PDT


A series of fossils unearthed in southwestern China has revealed the origins of complex life in unprecedented detail, and pushed its beginning back by at least 40 million years.

The specimens come from the Doushantuo formation, a layer of sediments deposited about 590 million years ago, just before the Ediacaran period's primordial fauna gave way to the kaleidoscopically complex creatures of the Cambrian explosion.

During the Ediacaran, even the most structurally complicated animals had flat bodies with simple symmetry, like living quilts or mattresses. It was only during the Cambrian that animals developed what's known as bilateral symmetry — a distinct front and back, top and bottom.

bilateria-11The Doushantuo fossils date to the cusp of this transition, and are so finely preserved that scientists can distinguish the structures of individual cells. The latest fossils, described Monday in the Proceedings of the National Academy of Sciences, aren't even fully formed animals, but embryos.

Using synchrotron radiation microtomography — a microscopy technique that combines thousands of of X-rays taken from different angles — researchers reconstructed the embryos in three-dimensional detail. They found that the embryos were bilaterally symmetrical, and were organized so differently that they belonged to two distinct taxonomic groups. For those groups to be so different, bilateral symmetry must have been around for a while. Some scientists have suspected as much, but without such solid evidence.

"These bilaterians had already diverged into distantly related groups at least 40 million years before the Cambrian radiation," wrote the researchers. "The last common ancestor of the bilaterians lived much earlier than is usually thought.

Images: PNAS

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Citation: "Complex embryos displaying bilaterian characters from Precambrian Duoshantou phosphate deposits, Weng'an, Guizhou, China." By Jun-Yuan Chena, David J. Bottjer, Gang Li, Michael G. Hadfield, Feng Gao, Andrew R. Cameron, Chen-Yu Zhang, Ding-Chang Xian, Paul Tafforeau, Xin Liao, and Zong-Jun Yin. Proceedings of the National Academy of Sciences, Vol. 106 No. 42, Oct. 20, 2009.

Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecosystem and planetary tipping points.

Why Pygmies Are Small

Posted: 19 Oct 2009 03:14 PM PDT


The Grim Reaper can cut life short and, under the right circumstances, whittle those still standing down to the size of pygmies. That's the controversial conclusion of a new study, published in the October Current Anthropology, that found that stature declined as death rates rose in three small-bodied populations over a 115-year period.

sciencenews"We provide the first evidence that pygmy body sizes vary considerably over time, that they correlate strongly with mortality rates and that increasing mortality rates lead to even greater reductions of body size," says Jay Stock of the University of Cambridge in England.

Stock and Andrea Migliano, both anthropologists at the University of Cambridge, say that their findings support a scenario in which most females are able to reproduce at relatively young ages, probably in response to high mortality rates, This physical trait then becomes more common from one generation to the next. Early-maturing bodies divert physiological resources away from growth, yielding small bodies as a side effect, the researchers hypothesize.

Critics of this argument suspect that environmental challenges, such as nutritional deficiencies or cramped forest quarters, prompted the evolution of short-statured populations.

Researchers have traditionally defined pygmies as populations with an average adult male height of no more than 155 centimeters, or about 5 feet, 1 inch. Hunter-gatherer groups classified as pygmies live in various regions, including Africa, Indonesia, the Philippines and the Andaman Islands, which lie southeast of Burma.

Stock and Migliano analyzed data from 11 British government and anthropological studies of Andaman Islanders conducted between 1871 and 1986. Investigations included a range of health and physical measures for 604 individuals from three pygmy groups — the Great Andamanese, the Onge and the Jarawa. Data also included population approximations for each group across time.
Despite describing a small number of people who may have been assessed with varying degrees of accuracy, these studies provide the only long-term glimpse of growth changes within different pygmy groups, Stock says.

British colonies were first established on the Andaman Islands in 1858 and remained until 1947. Onge and Jarawa pygmies, who lived on separate islands, retreated into forests to avoid the British. Great Andamanese pygmies befriended the newcomers.

As a result, Great Andamanese individuals were exposed to infectious diseases against which they had no defense, including influenza, tuberculosis, measles and syphilis. Their approximate numbers dropped from 6,000 in 1858 to 600 in 1900. A low of 19 Great Andamanese individuals was recorded during the 1960s, but the population survives.

British historical records show that average heights for the Great Andamanese dropped markedly during the period of increased mortality, Stock and Migliano say. From 1879 to 1927, the average height of men who were measured decreased at a rate equivalent to 4.7 centimeters, or nearly 2 inches, every 100 years. Measured height declines for women were equivalent to 1.8 centimeters, or almost three-quarters of an inch, every 100 years.

Data from the 19th century were unavailable for the other two pygmy groups that avoided the British. But Onge men and women displayed average height increases from 1927 to 1962, after British attempts to interact with them had stopped. Onge population numbers declined from 1901 to 1951, although not as steeply as among the Great Andamanese.

Jarawa individuals were first measured in 1985. Average heights of 155 centimeters for men and 147 centimeters, or about 4 feet, 10 inches, for women exceeded all average heights recorded for the other two pygmy groups.

Population estimates for the Jarawa held stable during the colonial period, the researchers say.

A related 2007 study led by Migliano reported that pygmies in Africa and the Philippines tend to stop growing by early adolescence, have low life expectancies and begin reproducing at younger ages than taller hunter-gatherers. That pattern of findings also fits the idea that pygmy-sized bodies occur as a by-product of an evolved tendency for women to become fertile early in life, Stock says.

Anthropologist Brian Shea of Northwestern University calls such evidence "interesting but irrelevant to the origin of small body size in human pygmy groups." Stock and Migliano document short-term, environmentally induced changes in height that would affect the size of any population, Shea contends. This process can't explain the origin of pygmies, he says.

He and a colleague have measured differing limb proportions in East African and West African pygmies. Other researchers have found slowed growth during childhood for Africa's Mbuti pygmies, apparently due to reduced levels of a key growth hormone. Such data suggest that these groups have evolved small bodies in direct response to as yet unidentified, long-term challenges in distinctive habitats, Shea says.

Despite past high mortality rates, Stock and Migliano have no solid evidence that any Andaman Island pygmies mature exceptionally fast, remarks anthropologist Barry Bogin of Loughborough University in England. Historical accounts indicate that Andaman Island females married at ages as young as 11, but those sources don't Indicate whether the girls were sexually mature at marriage, Bogin notes.

Stock and Migliano found no evidence of malnutrition, but they can't rule out that that a lack of one or more essential nutrients in the diets of Andaman Island pygmies impeded growth, he adds.

"Longitudinal studies of pygmies and other short-statured people, with detailed nutritional and health information, are the only way to study this issue," Bogin says.

Image: German anthropologist Egon von Eickstedt posed with Onge hunter-gatherers during a trip to the Andaman Islands in 1928./ Haddon Library, University of Cambridge

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