Paleoanthropology Migration

Global Positioning

New fossils revise the time when humans colonized the earth

Scientists have long known that hominids arose in Africa, and for the first few million years they stayed there. But at some point our ancestors began to move out of their motherland, marking the start of global colonization. Determining why and when they left, however, has proved difficult because of the scarcity of early human fossils. Now two ancient skulls from the Republic of Georgia provide the strongest evidence yet of the first humans to journey out of Africa. According to a report in the May 12 Science, they appear to have accomplished this far earlier—and with a much more modest technology—than many investigators had expected.

Researchers unearthed the skulls in Dmanisi, about 85 kilometers southwest of the Georgian capital, Tbilisi. Based on radiomet-ric dating of the volcanic layer underlying the fossils, paleomag-

ATAPUERCA, SPAIN T 0.78 MYA

ATAPUERCA, SPAIN T 0.78 MYA

DMANISI, GEORGIA 1.7 MYA

DMANISI, GEORGIA 1.7 MYA

, UBEIDIYA,ISRAEL 1 0-1.4 MYA

GONGWANGLING, CHINA !

1.1 MYA

TURKANA, KENYA 1.6-1.9 MYA

GONGWANGLING, CHINA !

1.1 MYA

OLDUVAI GORGE, TANZANIA 2-1.8 MYA

JAVA, INDONESIA 1.8 MYA? MYA = MILLION YEARS AGO

HUMANS LEFT AFRICA EARLY, according to two new Georgian fossils, one of which is shown here (inset). Previous estimates based on ages of known fossils (map) had suggested a much later dispersal.

netic measurements and the presence of animal species whose age has been documented elsewhere, the team dated the skulls to around 1.7 million years ago—at least 300,000 years older than stone tools from a site in Israel called 'Ubeidiya that were considered the oldest undisputed traces of humans outside Africa.

The finding—coupled with previously known fossils from Dmanisi whose antiquity was originally doubted—overturns a popular theory aimed at explaining what prompted the first colonizers to venture out of Africa. The stone tools from 'Ubeidiya represent an advanced industry known as Acheulean, which includes carefully crafted hand axes and other double-edged tools well suited to carving meat. The earliest Acheulean tools come from Africa and date to about 1.6 million years ago. Prior to that, hominids were using a more primitive technology dubbed Oldowan. Re searchers thus proposed that the development of the Acheulean enabled early humans to finally leave Africa, because the tools gave them a better means of scavenging and hunting. Dmanisi, however, has yielded Oldowan, not Acheulean, tools.

Taking that into consideration, a more viable explanation for the dispersal stems from anatomical shifts rather than new technology, according to team member David Lordkipanidze of the Georgia State Museum. The Dmanisi hominids most closely resemble an early member of our genus that some researchers call Homo ergaster (others prefer the designation early African H. erectus, and still others call it early H. sapiens). With the emergence of this form around two million years ago, says University of Michigan paleoanthropologist Milford H. Wolpoff, "we get someone who is three times the weight and twice the height of all australopithecines, with really long legs." The only way to maintain this body size, he notes, is through a higher-

quality diet than that of the australopithecines. Higher quality, in this case, probably meant including meat. With long legs, Homo was well equipped to patrol the larger home range that car-nivory requires. After adopting this hunter-gatherer subsistence strategy, it was only a matter of time before these ancient humans expanded into Eurasia.

Indeed, researchers will most likely uncover Eurasian remains even older than Dmanisi, surmises Susan C. Antón, a paleoanthropologist at the University of Florida and member of the Dmanisi research team. Remains from Java hint at human occupation as early as 1.8 million years ago, and getting there would have required moving through Eurasia. Although many scholars regard the date assigned to these fossils with a great deal of skepticism, early Homo certainly could have reached Southeast Asia within that time frame, according to Harvard University archaeologist Ofer Bar-Yosef. In fact, he estimates that such a dispersal would have taken hunter-gatherers only a few thousand years. (Importantly, as with Dmanisi, the only tools known from the earliest East Asian sites are of the Oldowan variety.)

Early dates for Java aside, humans had reached eastern China by 1.1 million years ago. Yet the earliest accepted Europeans are 780,000-year-old fossils from Spain. Why they appear to have taken so long to reach western Europe, which is closer to the exit route from Africa than is East Asia, remains unclear. One theory posits that large-jawed carnivores, which left little for scavengers, prevented humans from establishing a foothold there. Others imagine that inhospitable climate and geography thwarted early European colonization. But Bar-Yosef suspects that older European sites will turn up, demonstrating that some of the emigrating groups headed from Africa into Mediterranean Europe. A more conservative view comes from Antón, who doubts that any older fossils will come from that region. Then again, she remarks, "Dmanisi really shows us how little we know about the potential sites that are out there." —Kate Wong

^ PSYCHOLOGY GROUP DYNAMICS

More Than the Best Medicine

^^ Hear the one about the baboon with the wooden leg? Laughing to make friends and influence others

ITHACA, N.Y.—Psychologist Jo-Anne Bachorowski of Van-derbilt University has learned an important lesson from her research on laughter: "I know now to snort and grunt only with friends but never around men I want to impress." Bachorowski, her Vanderbilt colleague Moria Smoski and Michael J. Owren of Cornell University have tested how men and women respond to and use laughter. They have discovered that the quality of a laugh can make someone more or less attractive. More interesting, other people in the room affect how much, and in what form, someone laughs. Women laugh more wildly around male strangers, but men laugh most with their buddies. And these differences, the researchers suggest, make evolutionary sense.

In one experiment, subjects listened to recorded laughs and were asked to "rate" the sound: Would they like to meet the laugher? Unvoiced laughs—like that of your friend who opens his mouth, rocks back and forth, and pants like a hyena—failed to attract any interest. Snorters and grunters, especially women,

CHUCKLEFEST: A scene from Monty Python and the Holy Grail was used to determine how men and women laugh in particular social situations. Hint: to be attractive, avoid snorting.

were also not high on anybody's list. But the woman with the singsong laugh, well, she could have a date every night. Such women were rated as even friendlier and sexier than men with the same kind of laugh.

To get at exactly how laughing influences a social situation, the investigators then asked the subjects, alone or paired with a friend or with a stranger, to watch film clips. Among them were the fake orgasm scene from When Harry Met Sally and the "Bring out your dead" skit from Monty Python and the Holy Grail. Who wouldn't laugh?

These people certainly did, but in unexpected ways. Women laughed more with male friends than with female friends. More interesting, their laughs were more highly pitched—that is, more extreme—when they were with a male they had never met. Alone or with other women, they were more subdued. The men, in contrast, laughed more, and more extremely, with their male friends.

Laughing obviously is not just an emotional reaction but also a social signal. Just what the signal is all about is unclear. "After all, there's no necessary reason to produce a laugh," comments Bachorowski, chuckling softly. Humans are the only creatures that laugh (stupid pet tricks aside). Clearly, other animals seem to feel happy—just watch two monkeys groom each other and see the body language of bliss—but they never laugh. Some, like chimpanzees, might smile occasionally, but it demonstrates submission and has nothing to do with feeling good or hearing a funny joke. Young chimps open their mouths and puff air when they play, and their behavior could be considered a precursor to human laughing. But it isn't close to the way humans of all ages laugh.

Owren and Bachorowski speculate that human laughter evolved as a unique way to make and break alliances. First came the smile, which must have communicated a positive emotional state to someone else; our ancient ancestors probably used those smiles to reassure one another and build alliances. But of course, smiles can be faked, and so what evolved as an honest signal was probably soon corrupted. Enter laughing, a much more complex signal. Laughing involves more neural systems, the use of vocal apparatus and lots of energy. "You have to be a much better actor to fake a laugh convincingly than fake a smile convincingly," Owren says. And so laughing probably replaced smiling at some point in human history as an honest signal in coalition building.

And the right laugh at the right time can even manipulate others. When the women in this study laughed more wildly with male strangers, they may have been unconsciously arousing the men. Not in a sexual way, but enough to make the guy feel positive. That's a good idea, because unfamiliar males pose a physical and sexual threat to women. "When women have men in this state—in a good mood and ever hopeful [for sex]—they are more malleable," Owren theorizes. In the same way, when the men in the experiment laughed the most with other men, they were probably honoring the age-old tradition of the buddy system, reinforcing those male bonds with a good guffaw.

To test their hypothesis further, the researchers are now looking at how laughing affects more complex social situations, such as game playing, and they hope to use medical imaging techniques to follow the path of laughter through the brain. Meanwhile remember this: the next time you laugh, avoid the snort and make a cheery noise, unless you're alone or want to be.

—Meredith F. Small

MEREDTH F. SMALL is a writer and a professor of anthropology at Cornell University. Her latest book is Our Babies, Ourselves: How Biology and Culture Shape the Way We Parent (Dell, 1999).

^ GROWTH POPULATION

" The U.S. Population Race

In the standard demographic scheme, population change results from three forces: births, deaths and migration. In the period 1970-1999 the U.S. saw about 110 million births and 63 million deaths, a natural increase of 47 million. Domestic migration was far greater: there were 425 million occasions in which Americans moved to another county in the same state or to a different state altogether. (The more than 750 million occasions in which Americans moved within counties are not reflected in the map.) The 38 million who migrated to the U.S. from abroad had a small effect overall on the redistribution of population, except in a few areas such as New York City.

Technology and the economy, of course, largely govern regional migration. The long-term decline of population in the Buffalo and Pittsburgh regions traces mostly to the crisis in heavy manufacturing of the 1980s. Because other industries could not absorb the laid-off workers, many job seekers relocated, particularly the young. Those who stayed, being older, had fewer children. The demographic shock was so great that populations in these areas are still about 15 percent below 1970 levels.

Other regions suffered similar shocks in the 1980s yet recovered. The Min-neapolis-St. Paul region, for example, successfully rebounded after its mainframe-computer business collapsed precipitously. Attracting new industry has long been the goal of municipal boosters, but the Minneapolis-St. Paul region, with its high taxes and daunting winter climate, expanded primarily by developing a diversified homegrown industrial base, mainly in medical technology built from local expertise in health care.

High-tech, of course, has driven the spectacular growth apparent in many areas, notably in Silicon Valley and Seattle, but an older technology was perhaps just as important for the South. The spread of air-conditioning after World War II made Southern living tolerable. This, together with the growth of the interstate high

City Populations Map

Change in population by county, 1970 □ Loss □ 0 - 24.9 □ 25 - 49.9

- 1999 (percent) 150 or more

SOURCE: U.S. Bureau of the Census way system and long-distance trucking, low labor costs, and weak unions, allowed the South to compete aggressively with Northern manufacturers. Technology had the opposite effect in agricultural areas in the Great Plains. Although these places are generally prosperous, population has been declining since the 1930s because farms have been consolidating and becoming increasingly more productive, and so opportunities for young people there have declined.

If diversity and wealth beget a growing population, lack of diversity and poverty beget population decline, as happened in the Mississippi Delta, which has been losing people for most of the past 60 years. The delta, which runs from southern Missouri to Vicksburg, Miss., and northern Louisiana and includes counties in four states, has one of the poorest, least educated populations in the U.S., a major deterrent to modern industry. The delta is traditionally a land of sharecroppers, but since 1950 technology has reduced the need for unskilled field labor. So young people, particularly those with some education, went elsewhere.

High costs of doing business, including high taxes, may depress population size, as happened in New York City, which was a leading manufacturing center as recently as the 1960s. Low-cost areas such as the Atlanta region have benefited, although that city has also prospered because of its diversified economy, access to air and ground transportation, skilled workforce, and early abandonment of retrogressive racial attitudes.

Rising affluence has led a growing number of people to spend more on recreation and second homes. That has fueled population increases not only in places such as Florida and the Southwest but also in the Ozark Plateau of eastern Oklahoma-northern Arkansas-southern Missouri, the northern part of the lower Michigan peninsula and most of the nation's coastal areas.

—Rodger Doyle ([email protected])

MEDICINE

<u DNAJunk and Lupus

hen the trash collector doesn't come, the waste may become dangerous to health. A similar negligence might cause the severe autoimmune disease systemic lupus erythematosus, which affects more than one million people in the U.S. When a body cell dies, a crew of proteins quickly chops it up and clears the remnants. But if molecules such as DNA are left behind, antibodies can develop against them and lead to inflammation.

To test if failure to remove the DNA from dead cells can alone elicit lupus, researchers from the universities of Essen and Bochum in Germany, led by TarikMoroy, created mice lacking the DNA-clearing enzyme called Dnase-1. In the June issue of Nature Genetics they report that after six to eight months, some of these genetically engineered mice had indeed developed antibodies against DNA and a form of kidney inflammation common in lupus. Because Dnase-1 activity is also low in lupus patients, treating them with the enzyme might improve their condition. — Julia Karow

PSYCHOLOGY

Size Doesn't Matter

^ ince the mid-1970s psychologists have maintained that children in large families tend to score lower on IQ tests. But data appearing in the June American Psychologist now show that birth order and family size have no bearing on a kid's IQ. Over a six-year period, investigators led by Joseph Lee Rodgers of the University of Oklahoma gave IQ tests to 5,107 children born to participants ofthe National Longitudinal Survey ofYouth, a random sample of families started in 1972. IQ scores were then compared within families, not just between families—something earlier studies had not done. The researchers failed to find any correlation between family size, birth order and IQ. Instead they found that women with lower IQ scores tend to have larger families and discovered a link between the mother's IQ and those of her children, no matter how many there are. Parents should now feel comfortable about having more than 1.85 kids. —Diane Martindale

GALAXY MAPPING

Cosmic Cartography

osmologists have a reputation for thinking about ridiculously large things (the universe) or ridiculously small things (particles). But one of their greatest challenges has been to unravel what happens on medium scales— at cosmic distances where matter goes from being clumpy on small scales to being comparatively smooth on larger ones. Now an ongoing galaxy-mapping effort has seen the transition: it begins to occur at around 300 million light-years. The arrangement of matter on such scales reflects the overall density ofthe universe, and the results agree with the current consensus among cosmologists. The findings come from the Two-Degree Field (2dF) galaxy red-shift survey. It ultimately intends to plot the positions of 250,000 galaxies in two slices ofthe sky, each about 75 degrees across, eight to 15 degrees thick, and four billion light-years deep—more than twice as deep as the previous record-holder. The survey team, led by Matthew Colless

AS BIG AS IT GETS: Galaxies belong to clusters, which belong to superclusters, which belong to "walls," which belong to ... nothing. The walls in this map of 106,000 galaxies are not part of any larger subunit.

ofthe Australian National University and John A. Peacock ofthe University of Edinburgh, described its progress at the June American Astronomical Society meeting. — George Musser

OCEANOGRAPHY

Sea Change for Tides C

^ta» omputer models that mimic the circulation of the world's oceans, the primary engine of climate change, are programmed to ignore tides. That's because the moon's gravity tugs the oceans back and forth but doesn't mix them up and down, which is the way the ocean absorbs and releases heat. But now a report in the June 15 Nature, based on sea-level measurements by the TOPEX/ Poseidon satellite, suggests that energy dispersed from lunar tides could drive some of the vertical mixing. Friction between the water and shallow coastlines diffuses most tidal energy but does not account for about 30 percent of it. That energy is being rerouted by underwater mountain chains and other rough spots, such as the Mid-Atlantic Ridge. Globally, these rough spots scatter about a trillion watts of energy-half the power needed to return deep waters to the surface. —Sarah Simpson

HIGH TIDE (pink)

LOW TIDE (blue)

HIGH TIDE (pink)

LOW TIDE (blue)

DATA POINTS

The Need for Zzz's

Average number of hours a day a U.S. adult sleeps today: 7 Number of hours in 1910: 9

Percentage of adults who sleep 6 1/2 hours or less: 33

Percentage of employees who would nap at work if allowed: 33 Percentage of employers who allow napping: 16

Percentage of adults who admit to driving while sleepy: 51 Percentage of adults who admit to driving faster while sleepy: 12 Number of accidents caused by drowsy driving each year: 200,000 ^

Number of milligrams of caffeine in eight ounces of:

Brewed drip coffee: 100 Starbucks coffee: 200 Espresso (one ounce): 40 Brewed U.S. teas: 40 Green tea: 33 Pepsi-Cola: 25 Coca-Cola Classic: 31

SOURCES: National Sleep Foundation; U.S. Food and Drug Administration; International Food Information Council; Starbucks; Mayo Clinic; Pepsico; Coca-Cola Company

Percentage of adults who admit to driving while sleepy: 51 Percentage of adults who admit to driving faster while sleepy: 12 Number of accidents caused by drowsy driving each year: 200,000 ^

SOURCES: National Sleep Foundation; U.S. Food and Drug Administration; International Food Information Council; Starbucks; Mayo Clinic; Pepsico; Coca-Cola Company

BIOLOGY

Atomic-Force Geckos

ow can a gecko climb up a glass wall and hang from one toe? In the June 8 Nature scientists offer a solution to this long-standing mystery. A gecko foot

bears about half a million hairs, or setae, each of which splits into hundreds of ends, like a brush (top photograph). The maximum adhesive force of a single seta reaches about 200 micronewtons, nearly 10 times higher than previously estimated from studies of whole animals. This means that if all its setae operated at once and at full force, the gecko could carry 40 kilograms. The setae let go when tipped at 30 degrees, explaining the gecko's "toe-peeling" walking style. Van derWaals forces, the weak attractive forces between atoms and molecules, most likely explain the adhesion; they require a distance between foot and surface of no more than one atom (also see www.sciam. com/explorations/ 2000/061900 Gecko). —J.K.

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