History > 2006 > USA > Science

Studies of Transcription of DNA

Bring Nobel Prize

October 4, 2006
By THE ASSOCIATED PRESS
Filed at 11:21 a.m. ET
The New York Times

STOCKHOLM, Sweden (AP) -- American Roger D. Kornberg, whose father won a Nobel Prize a half-century ago, was awarded the prize in chemistry Wednesday for his studies of how cells take information from genes to produce proteins.

The work is important for medicine, because disturbances in that process are involved in illnesses like cancer, heart disease and various kinds of inflammation. And learning more about the process is key to using stem cells to treat disease.

Kornberg, 59, a professor at the Stanford University School of Medicine, said medical benefits from his research have taken root.

''There are ... already many therapies, many drugs that are in development in trials or already available and there will be many more,'' he said. ''Significant benefits to human health are already forthcoming. I think there will be many many more.''

Kornberg's award, following the Nobels for medicine and physics earlier this week, completes the first American sweep of the Nobel science prizes since 1983.

Americans have won or shared in all the chemistry Nobels since 1992. The last time the chemistry Nobel was given to just one person was in 1999.

Kornberg's father, Arthur, shared the 1959 Nobel medicine prize with Severo Ochoa for studies of how genetic information is transferred from one DNA molecule to another.

The younger Kornberg said he remembered traveling to Stockholm with his father for the Nobel Prize award ceremonies.

''I have always been an admirer of his work and that of many others preceding me. I view them as truly giants of the last 50 years. It's hard to count myself among them,'' he said.

''Something so remarkable as this can never be expected even though I was aware of the possibility. I couldn't conceivably have imagined that it would become reality.''

The Kornbergs are the sixth father and son to both win Nobel Prizes. One father and daughter -- Pierre Curie and Irene Joliot-Curie -- won Nobel Prizes in physics and chemistry, respectively. Marie Curie -- Irene's mother and Pierre's wife -- won two Nobel prizes, for chemistry and physics.

Roger Kornberg's prize-winning work produced a detailed picture of what scientists call transcription in eukaryotes, the group of organisms that includes humans and other mammals, the Royal Swedish Academy of Sciences said in its citation.

Kornberg shed light on how information is taken from genes and converted to molecules called messenger RNA. These molecules shuttle the information to the cells' protein-making machinery. Proteins, in turn, serve as building blocks and workhorses of cells, vital to structure and functions.

Since 2000, Kornberg has produced actual pictures of messenger RNA molecules being created, a process that resembles building a chain link by link. The images are so detailed that individual atoms can be distinguished.

''In an ingenious manner Kornberg has managed to freeze the construction process of RNA half-way through,'' the Nobel committee said. That let him capture the process of transcription in full flow, which is ''truly revolutionary,'' the committee said.

''Kornberg realized ... that to get to the chemical details of the (process) was fundamental,'' said Anders Liljas, a member of the Nobel Committee in Chemistry. ''Because if you don't really see it on a molecular, atomic level, then you don't really understand it.''

Kornberg's breakthrough was published in 2001, remarkably recent for honoring by Nobel prize standards. But it followed a decade of researching yeast cells -- whose similarity to human cells Kornberg called ''perfectly astounding'' -- in search of a method to reveal the transcription process.

In those 10 years, Kornberg was allowed to continue his research without publishing a single major finding -- a rare luxury in the world of science where funders often want instant results, said Hakan Wennerstrom, chairman of the Nobel Committee for Chemistry.

''I guess it helps to have a father who is a Nobel laureate,'' Wennerstrom said. ''But he also had previous publications of the highest level.''

Jeremy M. Berg, director of the National Institute of General Medical Sciences in Bethesda, Md., which has supported Kornberg's work for more than 20 years, called Kornberg's prize ''fantastically well-deserved.''

The question of how information from genes is turned into RNA is fundamental, Berg said, and Kornberg ''started working on it when it seemed somewhere between ambitious and crazy'' to figure out the detailed structure and functioning of the cell's machinery for doing the job, he said.

''The last five years have been really breathtaking in terms of the details of the structures that he's been producing and what they're revealing about the mechanism, as well as laying the groundwork for future studies of how gene regulation works,'' Berg said.

Kornberg is the the fifth American to win a Nobel prize this year. So far, all the prizes -- medicine, physics and chemistry -- have gone to Americans.

Last year's Nobel laureates in chemistry were France's Yves Chauvin and Americans Robert H. Grubbs and Richard R. Schrock, who were honored for discoveries that let industry develop drugs and plastics more efficiently and with less hazardous waste.

Alfred Nobel, the wealthy Swedish industrialist and inventor of dynamite who endowed the prizes, left only vague guidelines for the selection committee.

In his will, he said the prize should be given to those who ''shall have conferred the greatest benefit on mankind'' and ''have made the most important chemical discovery or improvement.''

This year's Nobel announcements began Monday, with the Nobel Prize in medicine going to Americans Andrew Z. Fire and Craig C. Mello for discovering a powerful way to turn off the effect of specific genes, opening a potential new avenue for fighting diseases as diverse as cancer and AIDS. Their work dealt with how messenger RNA can be prevented from delivering its message to the protein-making machinery.

On Tuesday, Americans John C. Mather and George F. Smoot won the physics prize for work that helped cement the big-bang theory of how the universe was created and deepen understanding of the origin of galaxies and stars.

Each prize includes a check for $1.4 million, a diploma and a medal, which will be awarded by Sweden's King Carl XVI Gustaf at a ceremony in Stockholm on Dec. 10.

Associated Press Writer Karl Ritter in Stockholm and AP science writer Malcolm Ritter in New York contributed to this report.

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On the Net:

Nobel Prizes: http://www.nobelprize.org

    Studies of Transcription of DNA Bring Nobel Prize, NYT, 4.10.2006, http://www.nytimes.com/aponline/science/AP-Nobel-Chemistry.html?hp&ex=1160020800&en=ea1f82b281d5854e&ei=5094&partner=homepage

Study Says U.S. Has Lead in Nanotechnology

September 26, 2006
The New York Times
By BARNABY J. FEDER

The United States continues to lead the world in nanotechnology research, but the influence of the government’s multibillion investment in the field may take decades to become apparent, according to an assessment of the National Nanotechnology Initiative done for Congress.

The National Research Council’s hopeful but guarded analysis fulfilled a requirement in a 2003 law that the initiative be reviewed every three years.

The report concluded that coordination among the many arms of government involved in nanotechnology had improved since the adoption of the law, which transformed the research begun under President Bill Clinton into a permanent program with an annual budget topping $1 billion.

But the report cautioned that too little money was being invested in understanding the potential health and environmental risks of manipulating matter on such a small scale.

Nanotechnology refers to a rapidly expanding range of devices and industrial processes that manipulate atoms and small clusters of molecules — materials measuring from 1 to 100 nanometers, or billionths of a meter. At such dimensions, traditional materials can develop valuable behaviors, like unusual strength, electrical conductivity or invisibility to the naked eye, and can be recombined with other materials to form novel drugs, foods and devices.

It is assumed that nanotechnology will have a huge economic effect in the decades to come. But there is also concern that the novel materials will bring new safety risks that could take decades to be fully understood.

The Research Council report said that because nanotechnology was a foundation technology that makes other innovations possible, the research spending could logically be compared with early investments in computing and communications technology, whose influence took 20 to 40 years to become apparent.

But the report warned that as things stand now the government had neither enough consistency in the way investments are classified and tracked nor the management structure needed to accurately assess what it was getting for its nanotechnology spending.

It said the 50-member panel of public and private nanotechnology experts set up to advise the government’s technology managers was too broad and too busy elsewhere to provide much help in setting priorities, and should be replaced with a smaller, more dedicated group.

The report also urged the program’s managers to enlist the Labor and Education Departments in a more coordinated effort to get students and workers the training needed to cope with nanotechnology, bridging disciplines like biology, physics and materials engineering.

The finding that safety research is underfunded echoed a report last week by a panel of experts assigned by President Bush’s National Science and Technology Council. In testimony on that report last Thursday before the House Science Committee, some experts said that the less than $40 million being spent annually on such research was too little.

They also said that scientists at each agency were selecting their own projects independently without much central direction.

But, in a reflection of the challenges ahead, one leading expert told the committee that attempts to centrally dictate research priorities may not work as well as some people believe.

“I have to tell you that this area is so complex that I don’t know of any person or a small group of people who would be smart enough to be able to identify all the risks, set the priorities and lay out a so-called game plan,” said the expert, Arden L. Bement Jr., director of the National Science Foundation.

    Study Says U.S. Has Lead in Nanotechnology, NYT, 26.9.2006, http://www.nytimes.com/2006/09/26/technology/26nano.html

A Chip That Can Transfer Data Using Laser Light

September 18, 2006
The New York Times
By JOHN MARKOFF

SAN FRANCISCO, Sept. 17 — Researchers plan to announce on Monday that they have created a silicon-based chip that can produce laser beams. The advance will make it possible to use laser light rather than wires to send data between chips, removing the most significant bottleneck in computer design.

As a result, chip makers may be able to put the high-speed data communications industry on the same curve of increased processing speed and diminishing costs — the phenomenon known as Moore’s law — that has driven the computer industry for the last four decades.

The development is a result of research at Intel, the world’s largest chip maker, and the University of California, Santa Barbara. Commercializing the new technology may not happen before the end of the decade, but the prospect of being able to place hundreds or thousands of data-carrying light beams on standard industry chips is certain to shake up both the communications and computer industries.

Lasers are already used to transmit high volumes of computer data over longer distances — for example, between offices, cities and across oceans — using fiber optic cables. But in computer chips, data moves at great speed over the wires inside, then slows to a snail’s pace when it is sent chip-to-chip inside a computer.

With the barrier removed, computer designers will be able to rethink computers, packing chips more densely both in home systems and in giant data centers. Moreover, the laser-silicon chips — composed of a spider’s web of laser light in addition to metal wires — portend a vastly more powerful and less expensive national computing infrastructure. For a few dollars apiece, such chips could transmit data at 100 times the speed of laser-based communications equipment, called optical transceivers, that typically cost several thousand dollars.

Currently fiber optic networks are used to transmit data to individual neighborhoods in cities where the data is then distributed by slower conventional wire-based communications gear. The laser chips will make it possible to send avalanches of data to and from individual homes at far less cost.

They could also give rise to a new class of supercomputers that could share data internally at speeds not possible today.

The breakthrough was achieved by bonding a layer of light-emitting indium phosphide onto the surface of a standard silicon chip etched with special channels that act as light-wave guides. The resulting sandwich has the potential to create on a computer chip hundreds and possibly thousands of tiny, bright lasers that can be switched on and off billions of times a second.

“This is a field that has just begun exploding in the past 18 months,” said Eli Yablonovitch, a physicist at the University of California, Los Angeles, a leading researcher in the field. “There is going to be a lot more optical communications in computing than people have thought.”

Indeed, the results of the development work, which will be reported in a coming issue of Optics Express, an international journal, indicate that a high-stakes race is under way worldwide. While the researchers at Intel and Santa Barbara are betting on indium phosphide, Japanese scientists in a related effort are pursuing a different material, the chemical element erbium.

Although commercial chips with built-in lasers are years away, Luxtera, a company in Carlsbad, Calif., is already selling test chips that incorporate most optical components directly into silicon and then inject laser light from a separate source.

The Intel-Santa Barbara work proves that it is possible to make complete photonic devices using standard chip-making machinery, although not entirely out of silicon. “There has always been this final hurdle,” said Mario Paniccia, director of the Photonics Technology Lab at Intel. “We have now come up with a solution that optimizes both sides.”

In the past it has proved impossible to couple standard silicon with the exotic materials that emit light when electrically charged. But the university team supplied a low-temperature bonding technique that does not melt the silicon circuitry. The approach uses an electrically charged oxygen gas to create a layer of oxide just 25 atoms thick on each material. When heated and pressed together, the oxide layer fuses the two materials into a single chip that conducts information both through wires and on beams of reflected light.

“Photonics has been a low-volume cottage industry,” said John E. Bowers, director of the Multidisciplinary Optical Switching Technology Center at the University of California, Santa Barbara. “Everything will change and laser communications will be everywhere, including fiber to the home.”

Photonics industry experts briefed on the technique said that it would almost certainly pave the way for commercialization of the long-sought convergence of silicon chips and optical lasers. “Before, there was more hype than substance,” said Alan Huang, a former Bell Laboratories researcher who is a pioneer in the field and is now chief technology officer of the Terabit Corporation, a photonics start-up company in Menlo Park, Calif. “Now I believe this will lead to future applications in optoelectronics.”

    A Chip That Can Transfer Data Using Laser Light, NYT, 18.9.2006, http://www.nytimes.com/2006/09/18/technology/18chip.html?hp&ex=1158638400&en=a4e71a2f9459f956&ei=5094&partner=homepage

Melvin Schwartz Dies at 73; Won Nobel Prize in Physics

August 30, 2006
The New York Times
By KENNETH CHANG

Melvin Schwartz, who shared the 1988 Nobel Prize in Physics for generating a beam of wispy particles known as neutrinos, died Monday at a nursing home in Twin Falls, Idaho. He was 73 and lived in Ketchum, Idaho.

The cause was complications of Parkinson’s disease and hepatitis C, said his son, David.

The Nobel-winning experiment, conducted in the early 1960’s at Brookhaven National Laboratory on Long Island, provided physicists with a new way to study one of the universe’s fundamental forces: the weak interaction, which governs how atomic nuclei fall apart in certain types of radioactive decay.

It also showed for the first time that two types of neutrinos existed. (Other researchers later discovered a third.) Later in his life, Dr. Schwartz founded a computer security company and then returned to physics to oversee an ambitious atomic physics collider at Brookhaven.

In the 1950’s, physicists had trouble studying neutrinos, because although they are plentiful — billions of neutrinos produced by the sun pass through every person every second — they barely interact with other matter, and only rarely. Dr. Schwartz suggested that neutrinos might be easier to study if it was possible to create a beam of them in a laboratory.

“He was an original thinker,” said Nicholas P. Samios, a classmate of Dr. Schwartz during their undergraduate and graduate studies at Columbia in the 1950’s. “Previously people were just doing decays of particles. He said, ‘Why don’t we just reverse it?’ That was one of his great ideas.”

The experiment slammed high-energy protons into a piece of beryllium. The collisions tore apart the beryllium nuclei, generating evanescent particles that fell apart in a cascade of debris.

Part of the debris included particles that always came out in pairs, a muon — a heavy version of an electron — together with a neutrino. A 40-foot-thick wall of steel, made from old warship armor plate, filtered out the atomic debris, except for the ghostly neutrinos, which continued traveling in the same direction as the initial beam of protons.

The scientists could then study the occasional collisions between neutrinos in the beam and aluminum atoms in a 10-ton detector. Those collisions showed that the neutrinos produced in conjunction with muons were different from those produced in conjunction with electrons.

This work, the creation of a neutrino beam and the discovery of muon neutrinos, won Dr. Schwartz and his Columbia colleagues Leon M. Lederman and Jack Steinberger the Nobel Prize.

Born in New York City in 1932, Melvin Schwartz attended the Bronx High School of Science. He received his bachelor’s degree from Columbia in 1953 and a doctorate, also from Columbia, in 1958. After working as a research scientist at Brookhaven, he joined the Columbia faculty.

In 1966, he moved to Stanford University as a professor of physics.

But as high-energy physics became more elaborate, requiring ever larger teams to carry out experiments, Dr. Schwartz shifted to other endeavors that fit better with his entrepreneurial spirit.

“Physics was getting into big time — more formal, big committees, large groups,” Dr. Samios said. “That’s not Mel’s style.”

In 1970, Dr. Schwartz founded Digital Pathways, a company that made equipment that allowed people to log onto computer networks securely from outside locations. He left Stanford in 1983 to work full time at his company.

Then, in 1991, his old classmate Dr. Samios, who was then director of Brookhaven, persuaded him to return to physics. Dr. Schwartz moved back to New York, both as a professor at Columbia and an associate director of Brookhaven. Dr. Schwartz oversaw the building of four detectors at the Relativistic Heavy Ion Collider, known as RHIC (and pronounced rick), that is currently running at Brookhaven.

“What you see at RHIC today is just the imprint of Mel’s personality, his approach to physics, his decision making,” said William A. Zajc, a physicist who works on one of the detectors, known as Phenix. That detector, he added, was the “shotgun wedding” of three proposals that Dr. Schwartz rejected, a controversial decision possibly driven by budget constraints.

Dr. Schwartz, who had left physics because groups of dozens of researchers were too large for his taste, was now managing collaborations of 300 to 400 scientists, Dr. Zajc said.

Dr. Zajc, who was working on one of the rejected proposals, said that Dr. Schwartz’s decision was initially discouraging, but that RHIC has turned out an overwhelming success. “It was probably Mel’s intuition about how he thought things should proceed,” he continued. “He was an iconoclast. He was willing to wade into a field in which he had no real experience and trust his physics judgment.”

Dr. Schwartz moved to Idaho in 1997.

In addition to his son David, he is survived by his wife, Marilyn, of Ketchum; two daughters, Diana Bodell of Bolingbrook, Ill., and Betty Marcon of San Francisco; a brother, Bernard Schwartz of Walnut Creek, Calif.; and six grandchildren.

    Melvin Schwartz Dies at 73; Won Nobel Prize in Physics, NYT, 31.8.2006, http://www.nytimes.com/2006/08/30/obituaries/30schwartz.html

 Fossil Called Missing Link From Sea to Land Animals        NYT        6.4.2006
http://www.nytimes.com/2006/04/06/science/06fossil.html?hp&ex=
1144382400&en=f4bbf761f85f4c1b&ei=5094&partner=homepage

Fossil Called Missing Link

From Sea to Land Animals

April 6, 2006
The New York Times
By JOHN NOBLE WILFORD

Scientists have discovered fossils of a 375-million-year-old fish, a large scaly creature not seen before, that they say is a long-sought missing link in the evolution of some fishes from water to a life walking on four limbs on land.

In two reports today in the journal Nature, a team of scientists led by Neil H. Shubin of the University of Chicago say they have uncovered several well-preserved skeletons of the fossil fish in sediments of former streambeds in the Canadian Arctic, 600 miles from the North Pole.

The skeletons have the fins, scales and other attributes of a giant fish, four to nine feet long. But on closer examination, the scientists found telling anatomical traits of a transitional creature, a fish that is still a fish but has changes that anticipate the emergence of land animals — and is thus a predecessor of amphibians, reptiles and dinosaurs, mammals and eventually humans.

In the fishes' forward fins, the scientists found evidence of limbs in the making. There are the beginnings of digits, proto-wrists, elbows and shoulders. The fish also had a flat skull resembling a crocodile's, a neck, ribs and other parts that were similar to four-legged land animals known as tetrapods.

Other scientists said that in addition to confirming elements of a major transition in evolution, the fossils were a powerful rebuttal to religious creationists, who have long argued that the absence of such transitional creatures are a serious weakness in Darwin's theory.

The discovery team called the fossils the most compelling examples yet of an animal that was at the cusp of the fish-tetrapod transition. The fish has been named Tiktaalik roseae, at the suggestion of elders of Canada's Nunavut Territory. Tiktaalik (pronounced tic-TAH-lick) means "large shallow water fish."

"The origin of limbs," Dr. Shubin's team wrote, "probably involved the elaboration and proliferation of features already present in the fins of fish such as Tiktaalik."

In an interview, Dr. Shubin, an evolutionary biologist, let himself go. "It's a really amazing, remarkable intermediate fossil," he said. "It's like, holy cow."

Two other paleontologists, commenting on the find in a separate article in the journal, said that a few other transitional fish had been previously discovered from approximately the same Late Devonian time period, 385 million to 359 million years ago. But Tiktaalik is so clearly an intermediate "link between fishes and land vertebrates," they said, that it "might in time become as much an evolutionary icon as the proto-bird Archaeopteryx," which bridged the gap between reptiles (probably dinosaurs) and today's birds.

The writers, Erik Ahlberg of Uppsala University in Sweden and Jennifer A. Clack of the University of Cambridge in England, are often viewed as rivals to Dr. Shubin's team in the search for intermediate species in the evolution from fish to the first animals to colonize land.

H. Richard Lane, director of paleobiology at the National Science Foundation, said in a statement, "These exciting discoveries are providing fossil 'Rosetta Stones' for a deeper understanding of this evolutionary milestone — fish to land-roaming tetrapods."

The science foundation and the National Geographic Society were among the financial supporters of the research. Besides Dr. Shubin, the principal discoverers were Edward B. Daeschler of the Academy of Natural Sciences in Philadelphia and Farish A. Jenkins Jr., a Harvard evolutionary biologist. Casts of the fossils will be on view at the Science Museum of London.

Michael J. Novacek, a paleontologist at the American Museum of Natural History in Manhattan, who was not involved in the research, said: "Based on what we already know, we have a very strong reason to think tetrapods evolved from lineages of fishes. This may be a critical phase in that transition that we haven't had before. A good fossil cuts through a lot of scientific argument."

Dr. Shubin's team played down the fossil's significance in the raging debate over Darwinian theory, which is opposed mainly by some conservative Christians in this country, but other scientists were not so reticent. They said this should undercut the argument that there is no evidence in the fossil record of one kind of creature becoming another kind.

One creationist site on the Web (emporium.turnpike.net/C/cs /evid1.htm) declares that "there are no transitional forms," adding: "For example, not a single fossil with part fins, part feet has been found. And this is true between every major plant and animal kind."

Dr. Novacek responded: "We've got Archaeopteryx, an early whale that lived on land, and now this animal showing the transition from fish to tetrapod. What more do we need from the fossil record to show that the creationists are flatly wrong?"

Duane T. Gish, a retired official of the Institute for Creation Research in San Diego, said, "This alleged transitional fish will have to be evaluated carefully." But he added that he still found evolution "questionable because paleontologists have yet to discover any transitional fossils between complex invertebrates and fish, and this destroys the whole evolutionary story."

Dr. Shubin and Dr. Daeschler began their search on Ellesmere Island in 1999. They were attracted by a map in a geology textbook showing an abundance of Devonian rocks exposed and relatively easy to explore. At that time, the land had a warm climate: it was part of a supercontinent straddling the Equator.

It was not until July 2004, Dr. Shubin said, that "we hit the jackpot." They found several of the fishes in a quarry, their skeletons largely intact and in three dimensions. The large skull had the sharp teeth of a predator. It was attached to a neck, which allowed the fish the unfishlike ability to swivel its head.

If the animal spent any time out of water, said Dr. Jenkins, of Harvard, it needed a true neck that allowed the head to move independently on the body.

Embedded in the pectoral fins were bones that compare to the upper arm, forearm and primitive parts of the hand of land-living animals. The joints of the fins appeared to be capable of functioning for movement on land, a case of a fish improvising with its evolved anatomy. In all likelihood, the scientists said, Tiktaalik flexed its proto-limbs mainly on the floor of streams and might have pulled itself up on the shore for brief stretches.

In their report, the scientists concluded that Tiktaalik was an intermediate between the fishes Eusthenopteron and Panderichthys, which lived 385 million years ago, and early tetrapods. The known early tetrapods are Acanthostega and Ichthyostega, about 365 million years ago.

Tiktaalik, Dr. Shubin said, is "both fish and tetrapod, which we sometimes call a fishapod."

    Fossil Called Missing Link From Sea to Land Animals, NYT, 6.4.2006, http://www.nytimes.com/2006/04/06/science/06fossil.html?hp&ex=1144382400&en=f4bbf761f85f4c1b&ei=5094&partner=homepage

Still Evolving, Human Genes Tell New Story

March 7, 2006
By NICHOLAS WADE
The New York Times

Providing the strongest evidence yet that humans are still evolving, researchers have detected some 700 regions of the human genome where genes appear to have been reshaped by natural selection, a principal force of evolution, within the last 5,000 to 15,000 years.

The genes that show this evolutionary change include some responsible for the senses of taste and smell, digestion, bone structure, skin color and brain function.

Many of these instances of selection may reflect the pressures that came to bear as people abandoned their hunting and gathering way of life for settlement and agriculture, a transition well under way in Europe and East Asia some 5,000 years ago.

Under natural selection, beneficial genes become more common in a population as their owners have more progeny.

Three populations were studied, Africans, East Asians and Europeans. In each, a mostly different set of genes had been favored by natural selection. The selected genes, which affect skin color, hair texture and bone structure, may underlie the present-day differences in racial appearance.

The study of selected genes may help reconstruct many crucial events in the human past. It may also help physical anthropologists explain why people over the world have such a variety of distinctive appearances, even though their genes are on the whole similar, said Dr. Spencer Wells, director of the Genographic Project of the National Geographic Society.

The finding adds substantially to the evidence that human evolution did not grind to a halt in the distant past, as is tacitly assumed by many social scientists. Even evolutionary psychologists, who interpret human behavior in terms of what the brain evolved to do, hold that the work of natural selection in shaping the human mind was completed in the pre-agricultural past, more than 10,000 years ago.

"There is ample evidence that selection has been a major driving point in our evolution during the last 10,000 years, and there is no reason to suppose that it has stopped," said Jonathan Pritchard, a population geneticist at the University of Chicago who headed the study.

Dr. Pritchard and his colleagues, Benjamin Voight, Sridhar Kudaravalli and Xiaoquan Wen, report their findings in today's issue of PLOS-Biology.

Their data is based on DNA changes in three populations gathered by the HapMap project, which built on the decoding of the human genome in 2003. The data, though collected to help identify variant genes that contribute to disease, also give evidence of evolutionary change.

The fingerprints of natural selection in DNA are hard to recognize. Just a handful of recently selected genes have previously been identified, like those that confer resistance to malaria or the ability to digest lactose in adulthood, an adaptation common in Northern Europeans whose ancestors thrived on cattle milk.

But the authors of the HapMap study released last October found many other regions where selection seemed to have occurred, as did an analysis published in December by Robert K. Moysis of the University of California, Irvine.

Dr. Pritchard's scan of the human genome differs from the previous two because he has developed a statistical test to identify just genes that have started to spread through populations in recent millennia and have not yet become universal, as many advantageous genes eventually do.

The selected genes he has detected fall into a handful of functional categories, as might be expected if people were adapting to specific changes in their environment. Some are genes involved in digesting particular foods like the lactose-digesting gene common in Europeans. Some are genes that mediate taste and smell as well as detoxify plant poisons, perhaps signaling a shift in diet from wild foods to domesticated plants and animals.

Dr. Pritchard estimates that the average point at which the selected genes started to become more common under the pressure of natural selection is 10,800 years ago in the African population and 6,600 years ago in the Asian and European populations.

Dr. Richard G. Klein, a paleoanthropologist at Stanford, said that it was hard to correlate the specific gene changes in the three populations with events in the archaeological record, but that the timing and nature of the changes in the East Asians and Europeans seemed compatible with the shift to agriculture. Rice farming became widespread in China 6,000 to 7,000 years ago, and agriculture reached Europe from the Near East around the same time.

Skeletons similar in form to modern Chinese are hard to find before that period, Dr. Klein said, and there are few European skeletons older than 10,000 years that look like modern Europeans.

That suggests that a change in bone structure occurred in the two populations, perhaps in connection with the shift to agriculture. Dr. Pritchard's team found that several genes associated with embryonic development of the bones had been under selection in East Asians and Europeans, and these could be another sign of the forager-to-farmer transition, Dr. Klein said.

Dr. Wells, of the National Geographic Society, said Dr. Pritchard's results were fascinating and would help anthropologists explain the immense diversity of human populations even though their genes are generally similar. The relative handful of selected genes that Dr. Pritchard's study has pinpointed may hold the answer, he said, adding, "Each gene has a story of some pressure we adapted to."

Dr. Wells is gathering DNA from across the globe to map in finer detail the genetic variation brought to light by the HapMap project.

Dr. Pritchard's list of selected genes also includes five that affect skin color. The selected versions of the genes occur solely in Europeans and are presumably responsible for pale skin. Anthropologists have generally assumed that the first modern humans to arrive in Europe some 45,000 years ago had the dark skin of their African origins, but soon acquired the paler skin needed to admit sunlight for vitamin D synthesis.

The finding of five skin genes selected 6,600 years ago could imply that Europeans acquired their pale skin much more recently. Or, the selected genes may have been a reinforcement of a process established earlier, Dr. Pritchard said.

The five genes show no sign of selective pressure in East Asians.

Because Chinese and Japanese are also pale, Dr. Pritchard said, evolution must have accomplished the same goal in those populations by working through different genes or by changing the same genes — but many thousands of years before, so that the signal of selection is no longer visible to the new test.

Dr. Pritchard also detected selection at work in brain genes, including a group known as microcephaly genes because, when disrupted, they cause people to be born with unusually small brains.

Dr. Bruce Lahn, also of the University of Chicago, theorizes that successive changes in the microcephaly genes may have enabled the brain to enlarge in primate evolution, a process that may have continued in the recent human past.

Last September, Dr. Lahn reported that one microcephaly gene had recently changed in Europeans and another in Europeans and Asians. He predicted that other brain genes would be found to have changed in other populations.

Dr. Pritchard's test did not detect a signal of selection in Dr. Lahn's two genes, but that may just reflect limitations of the test, he and Dr. Lahn said. Dr. Pritchard found one microcephaly gene that had been selected for in Africans and another in Europeans and East Asians. Another brain gene, SNTG1, was under heavy selection in all three populations.

"It seems like a really interesting gene, given our results, but there doesn't seem to be that much known about exactly what it's doing to the brain," Dr. Pritchard said.

Dr. Wells said that it was not surprising the brain had continued to evolve along with other types of genes, but that nothing could be inferred about the nature of the selective pressure until the function of the selected genes was understood.

The four populations analyzed in the HapMap project are the Yoruba of Nigeria, Han Chinese from Beijing, Japanese from Tokyo and a French collection of Utah families of European descent. The populations are assumed to be typical of sub-Saharan Africa, East Asia and Europe, but the representation, though presumably good enough for medical studies, may not be exact.

Dr. Pritchard's test for selection rests on the fact that an advantageous mutation is inherited along with its gene and a large block of DNA in which the gene sits. If the improved gene spreads quickly, the DNA region that includes it will become less diverse across a population because so many people now carry the same sequence of DNA units at that location.

Dr. Pritchard's test measures the difference in DNA diversity between those who carry a new gene and those who do not, and a significantly lesser diversity is taken as a sign of selection. The difference disappears when the improved gene has swept through the entire population, as eventually happens, so the test picks up only new gene variants on their way to becoming universal.

The selected genes turned out to be quite different from one racial group to another. Dr. Pritchard's test identified 206 regions of the genome that are under selection in the Yorubans, 185 regions in East Asians and 188 in Europeans. The few overlaps between races concern genes that could have been spread by migration or else be instances of independent evolution, Dr. Pritchard said.

    Still Evolving, Human Genes Tell New Story, NYT, 7.3.2006, http://www.nytimes.com/2006/03/07/science/07evolve.html?hp&ex=1141707600&en=8224f14d7e91d5d4&ei=5094&partner=homepage