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.

The scientists provide powerful new evidence for a 30-year-old theory, proposed in a classic paper from Mary-Claire King and Allan Wilson of Berkeley. That 1975 paper documented the 99-percent similarity of genes from humans and chimps and suggested that altered gene regulation, rather than changes in coding, might explain how so few genetic changes could produce the wide anatomic and behavioral differences between the two.

Using novel gene-array technology to measure the extent of gene expression in thousands of genes simultaneously, this study shows that as humans diverged from their ape ancestors in the last five million years, genes for transcription factors -- which control the expression of other genes -- were four times as likely to have changed their own expression patterns as the genes they regulate.

Because they influence the activity of many "downstream" genetic targets, small changes in the expression of these regulatory genes can have an enormous impact.

"When we looked at gene expression, we found fairly small changes in 65 million years of the macaque, orangutan, and chimpanzee evolution," said study author Yoav Gilad, Ph.D., assistant professor of human genetics at the University of Chicago, "followed by rapid change, along the five million years of the human lineage, that was concentrated on these specific groups of genes. This rapid evolution in transcription factors occurred only in humans."

"For 30 years scientists have suspected that gene regulation has played a central role in human evolution," said Kevin White, Ph.D., associate professor of genetics and ecology and evolution at Yale and senior author of the study. "In addition to lending support to the idea that changes in gene regulation are a key part of our evolutionary history, these new results help to define exactly which regulatory factors may be important, at least in certain tissues. This helps open the door to a functional dissection of the role of gene regulation during the evolution of modern humans."

To measure changes in gene expression from different species, White and Gilad developed the first multi-species gene array. This allowed them to compare the level of expression of more than 1,000 genes between humans, chimps, orangutans and rhesus macaques – representing about 70 million years of evolution. To make the samples comparable, the researchers studied tissue from the liver -- one of the most homogeneous sources -- from five adult males from each of the four species.

They focused their search on expression levels of two sets of genes, those that remained largely unchanged across all four species, suggesting that there was little room -- or need -- for improvement, and those that changed most dramatically, usually in the human lineage -- an indication of powerful incentives to adapt to a changing environment.

Of the 1,056 genes from all four species, 60 percent had fairly consistent expression levels across all four species. "The expression levels of these genes seem to have remained constant for about 70 million years," the authors wrote, "suggesting that their regulation is under evolutionary constraint."

Many of these genes are involved in basic cellular processes. The authors suggest that altering the regulation of these fundamental and ancient genes may be harmful. In fact, five of the 100 most stable genes have altered expression levels in liver cancer.

When they also looked for human genes with significantly higher or lower expression levels, they found 14 genes with increased expression and five with decreased expression. While only ten percent of the genes in the total array were transcription factors, 42 percent of those with increased expression in humans were. None of those with lower expression were transcription factors. This pattern, the authors note, is consistent with "directional selection."

Previous studies have found that many of these same genes have also evolved rapidly in humans, accumulating changes in their coding sequence as well as in expression rates. "Together," they add, "these findings raise the possibility that the function and regulation of transcription factors have been substantially modified in the human lineage."

This is a very efficient way to make big changes with very little effort, according to Gilad. By altering transcription factors, the entire regulatory network can change with very few mutations, increasing the impact and minimizing the risk.

"The big question," he said, "is why are humans so different? What sort of changes in the environment or lifestyle would drive such a rapid shift in the expression of genes -- in this case in the liver -- in humans and in no other primate?"

Part of the answer, he suspects, is rapid alterations in diet, probably related to the acquisition of fire and the emerging preference for cooked food. "No other animal relies on cooked food," he said. "Perhaps something in the cooking process altered the biochemical requirements for maximal access to nutrients as well as the need to process the natural toxins found in plant and animal foods."

This is just the first of a series of similar studies, said Gilad, that will look at changes in gene expression over evolutionary time. The next steps are to look at larger arrays of genes and to focus on other tissue types.

Instead, they believe God created humans at one time "as is," the survey showed.

About 31 percent of respondents said they believe humans evolved, but God guided the process. Only 1.2 percent said they believe the scientific theory of evolution and "God had no part."

Researchers said people with lower levels of education, those who attend church regularly, those who are 65 or older and those who identify with the Republican Party are more likely to believe in the biblical story of the origin of humans.

The poll was conducted in September but no margin of error figures or other information was available.

The bodies were dressed in animal skins decorated with the teeth of wild animals and wrapped in tree bark. The remains were then placed in tombs lined with pine logs, sprinkled with powdered red ochre to symbolise blood and burned.

The burnt-out graves where then likely covered to create small mounds.

'We've been digging for 9 years, but there are still unanswered questions,' Marciniak told Rzeczpospolita of puzzling half-circles made of small bonfires researchers found near the graves.

The neatly chiselled walls and roofs, the big pillars and stone stairs, indicate that the caves were dug by men. Yet nobody knows for what purpose the ancient people excavated them. Not a single word about the caves has ever been found among China's numerous ancient records although their size has already ranked them as the biggest ever discovered so far in China.

Altogether, 36 caves have been found among the rolling Huashan hills, near the crystal-clear Xin'an River. Two of the caves are now open to visitors. The rest are still being cleaned of the mud that has accumulated inside. According to the excavation workers, there is a high possibility that the 36 caves may be connected to one another.

Huanxi cave, with a length of 140 metres and a size of 4,800 square metres, is one of the two now open to public. After a walk of 100 metres, you find a grand hall inside the cave, with pools, pillars and small rooms on each side.

A most mysterious discovery is the slope of the cave. The inclined plane of the walls has exactly the same slope as the outside hill. Yet according to the technology of that time, how could the ancient people have managed that?

Of all the 36 caves, the biggest is the Qingliang Cave, which is known as the "Underground Palace" due to its scale and magnificent layout. With a total length of 170 metres, the cave covers a space of 12,600 square metres. The original digging-out of the cave could have produced at least 50,000 cubic metres of stone.

Inside the cave there is a stone bridge above an underground river and with stone paths leading to different halls. A two-storey stone structure is nearby where visitors have a bird's eye view of the huge cave from a balcony. No food remains were found in the cave, nor any smoking or signs of fire. But without fire how could the ancient diggers have produced light in the cave?

Wild guesses

As there are no historical records telling why the ancient people dug the caves, a variety of guesses are made by tourists as well as by experts.

Some people hold that the ancient people dug the caves just to produce stone as, at that time, a large quantity of stone was needed to build the town. But if it was only for stone, why did they leave exquisite smoothed chisel marks on the walls and roofs?

Another hypothesis is that the caves were used to station troops. According to history texts, a large-scale peasant uprising occurred near the caves in 1120. The caves could have been the place to station soldiers.

Yet as mentioned before, the stone tests showed that the caves have a history as long as 1,500 years, so the caves were already there before the peasant uprising.

Some hold that the caves were not the project of one dynasty or one period. They might have been dug out over hundreds of years. During the initial period, they were excavated just for the stone. But later people found the caves and after further digging, they made them bigger and longer for hiding in, stationing troops or simply as stock houses. This hypothethis well explains why even the same cave has different patterns of calving and different chisel marks.

Apart from all these hypotheses, there are many other guesses - for instance the caves might have been imperial tombs. But, later for whatever reason, the caves were abandoned.

All these unanswered questions place a shroud of mystery over the caves, as well as adding more fun to the trip.

The team, led by Joachim Saur at the University of Cologne, found the anti-planetary electrons, as they are called, using the instruments on NASA's Cassini spacecraft, including the Low Energy Magnetospheric Measurement System, or LEMMS.

Cassini's rotation helped the researchers determine the direction, number and strength of the electrons. They compared the results with recordings of the auroras in the polar region and a global model of Saturn's magnetic field. They found that the weakest auroras, or their absence, matched up very well with the lowest point of the magnetic field lines in which electron rays were measured.

Auroras occur on Earth when electrons above the atmosphere accelerate downward toward the poles. They emit visible light - usually vivid shades of red, green, blue and yellow - when they hit the planet's upper atmosphere.

Some years ago, scientists discovered that some electrons in the polar region accelerate away from Earth - or backwards. These anti-planetary electrons do not cause the sky to light up, and scientists have been puzzled about how they originate.

Until recently it also has been unclear whether anti-planetary electrons occur elsewhere in the solar system. They have been discovered in Jupiter's powerful magnetic field, and now Saur's team has discovered them on Saturn.

The backward electrons tend to be strongly focused, with an angle of beam spread less than 10 degrees, so the researchers were able to determine the location of their source: somewhere above the polar region, but inside a maximum distance of five radii of Saturn.

Because the electron beams have been measured on Earth, Jupiter and Saturn, and because they display similar characteristics, scientists now think they must share some fundamental underlying process - something that must be researched further.

Team members Norbert Krupp, and colleagues Andreas Lagg and Elias Roussos at the Max Planck Institute for Solar System Research in Katlenburg-Lindau, worked closely with scientists from the Institute for Geophysics and Meteorology at the University of Cologne, and the Applied Physics Laboratory of Johns Hopkins University in Baltimore. The APS team, led by Tom Krimigis, service and coordinate the LEMMS on Cassini.

Pulsars are dense, highly magnetized neutron stars born in supernovas. They act like cosmic lighthouses because they project rotating beams of radio waves.

"Pulsars are a physicist's dream come true, said team leader Michael Kramer. "They are made of the most extreme matter that we know of in the universe, and their highly stable rotation makes them super-precise cosmic clocks - but, embarrassingly, we do not know how these clocks work. This discovery goes a long way towards solving this problem."

Reporting Feb. 23 in Science Express, an online service of the journal Science, Kramer and colleagues said the pulsar appears normal for about a week, then "switches off" for about one month before emitting pulses again. The pulsar, called PSR B1931+24, is unique in this behavior. Because it is quiet most of the time, it has been difficult to detect -which suggests there may be many other similar objects in the universe.

"After the discovery of pulsars, theoreticians proposed that strong electric fields rip particles out of the neutron star surface into a surrounding magnetized cloud of plasma called the magnetosphere," said team member Andrew Lyne, "but for nearly 40 years, there had been no way to test whether our basic understanding was correct."

The astronomers said they were delighted when they discovered that PSR B1931+24 slows down rapidly when it is transmitting. "We can clearly see that something hits the brakes when the pulsar is on," said team member Christine Jordan.

The astronomers think the braking mechanism must be related to the radio emission and the processes creating it – such as the rotational energy carried by the wind of particles leaving the pulsar's magnetosphere. "Such a braking effect of the pulsar wind was expected but now, finally, we have observational evidence for it," said Duncan Lorimer, another team member.

Kramer said the amount of braking could be related to the number of charges leaving the pulsar magnetosphere – something that theorists had proposed 37 years ago, and the new observations matched within 2 percent. "We were really shocked when we saw these numbers on our screens," Kramer said. "Given the pulsar's complexity, we never really expected the magnetospheric theory to work so well."

Lyne called the finding "amazing," and added that, "after almost 40 years, we have not only found a new, unusual, pulsar phenomenon but also a very unexpected way to confirm some fundamental theories about the nature of pulsars."

CG4 is a star-forming region within the Milky Way with enough material to produce several stars the size of the Sun. Its head is about 1.5 light years wide and has been sculpted into the shape of an open mouth by radiation from hot, nearby stars, whose scattered light also causes CG4 to glow.

The eel appears on the verge of devouring a spiral galaxy called ESO 257-19. But fortunately, that galaxy is safely out of reach, actually lying more than 100 million light years farther away than CG4.

The image was taken by a 64-megapixel camera on the US National Science Foundation's 4-metre Victor M. Blanco telescope at Cerro Tololo Inter-American Observatory. It is a composite of four "colours" – blue, green, near-infrared and hydrogen-alpha, a wavelength of red light produced by warm hydrogen gas.

The composite is the 1000th image posted in the US National Optical Astronomy Observatory's online image gallery.

The phenomena also may explain how astrophysical entities like solar flares maintain their extreme temperatures.

The very high radiation output also creates new experimental environments to help validate computer codes responsible for maintaining a reliable nuclear weapons stockpile safely and securely -- the principle mission of the Z facility.

"At first, we were disbelieving," says Sandia project lead Chris Deeney. "We repeated the experiment many times to make sure we had a true result and not an 'Ooops'!"

The results, recorded by spectrometers and confirmed by computer models created by John Apruzese and colleagues at Naval Research Laboratory, have held up over 14 months of additional tests.

A description of the achievement, as well as a possible explanation by Sandia consultant Malcolm Haines, well-known for his work in Z pinches at the Imperial College in London, appeared in the Feb. 24 Physical Review Letters.

Sandia is a National Nuclear Security Administration laboratory.

What happened and why?

Z's energies in these experiments raised several questions.

First, the radiated x-ray output was as much as four times the expected kinetic energy input.

Ordinarily, in non-nuclear reactions, output energies are less -- not greater -- than the total input energies. More energy had to be getting in to balance the books, but from where could it come?

Second, and more unusually, high ion temperatures were sustained after the plasma had stagnated -- that is, after its ions had presumably lost motion and therefore energy and therefore heat -- as though yet again some unknown agent was providing an additional energy source to the ions.

Sandia's Z machine normally works like this: 20 million amps of electricity pass through a small core of vertical tungsten wires finer than human hairs. The core is about the size of a spool of thread. The wires dissolve instantly into a cloud of charged particles called a plasma.

The plasma, caught in the grip of the very strong magnetic field accompanying the electrical current, is compressed to the thickness of a pencil lead. This happens very rapidly, at a velocity that would fly a plane from New York to San Francisco in several seconds.

At that point, the ions and electrons have nowhere further to go. Like a speeding car hitting a brick wall, they stop suddenly, releasing energy in the form of X-rays that reach temperatures of several million degrees -- the temperature of solar flares.

The new achievement -- temperatures of billions of degrees -- was obtained in part by substituting steel wires in cylindrical arrays 55 mm to 80 mm in diameter for the more typical tungsten wire arrays, approximately only 20 mm in diameter. The higher velocities achieved over these longer distances were part of the reason for the higher temperatures.

(The use of steel allowed for detailed spectroscopic measurements of these temperatures impossible to obtain with tungsten.)

Haines theorized that the rapid conversion of magnetic energy to a very high ion plasma temperature was achieved by unexpected instabilities at the point of ordinary stagnation: that is, the point at which ions and electrons should have been unable to travel further. The plasma should have collapsed, its internal energy radiated away. But for approximately 10 nanoseconds, some unknown energy was still pushing back against the magnetic field.

Haines' explanation theorizes that Z's magnetic energies create microturbulences that increase the kinetic energies of ions caught in the field's grip. Already hot, the extra jolt of kinetic energy then produces increased heat, as ions and their accompanying electrons release energy through friction-like viscous mixing even after they should have been exhausted.

High temperatures previously had been assumed to be produced entirely by the kinetic flight and intersection of ions and electrons, unaided by accompanying microturbulent fields.

Z is housed in a flat-roofed building about the size and shape of an aging high-school gymnasium.

This work has already prompted other studies at Sandia and at the University of Nevada at Reno.