XIME W6 of the week

Fossil Skull Diversifies Farnilv Tree Anthropologists have long held that

the earliest members of the human evolu- tionary family consisted of a group of closely related species known as australo- pithecines. A 3.5million-year-old skull un- earthed in Kenya now suggests that the australopithecines had a set of evolution- ary companions.

west of Kenya’s Lake Turkana. Dating of volcanic rock from below and above the finds-based on measures of potassium and argon isotopes in the rock-places them at about 3.5 million years old.

K. platyops and A. afarensis may have evolved in substantially different habi- tats, the investigators theorize. Other

theresearchers have assigned two Newly discovered skull of Kenyanthropus to K. platyops. platyops (left) flanks a skull of Homo

If anthropologists accept Kenyan- rudolfensis, which may be reassigned to the thropus into the evolutionary fold, it genus Kenyanthropus. will. change their thinking about early hominids. Consider the new skull’s unusual anatomy. Like Australopithecus afarensis-a species that existed from 4 million to 3 million years ago and in- cludes the partial skeleton named Lucy-K. platyops has a small brain and thickly enameled cheek teeth. Moreover, its small ear holes resemble those of both chimpanzees and an earlier ho- minid, Australopithecus anamensis.

In other respects, though, K. platyops looks like a 2-million-year-old skull previ- ously found in Kenya. Many researchers attribute that specimen to Homo rudolfen- sis, an extinct species in our own genus. Leakey’s group reassigns the skull to Kenyanthropus based on such shared traits as a flat, sloping lower face, raised cheeks, and flattened brow ridges.

If K. platyops had deeper evolutionary roots than A. afarensis, as well as a unique relationship to H. rudolfensis, a species that emerged much later, it rais- es doubts about Lucy’s legacy, Leakey’s team contends. Contrary to the most in- fluential current view, her kind might not have given rise to all ensuing hominids, the team says.

Whether or not the new skull repre- sents a unique genus, it indicates that a distinct line of hominids existed along- side A. afarensis, remarks William H. Kim- be1 of the Institute of Human Origins in Tempe, Ariz. Further study of Leakey’s finds may resolve whether A. afarensis truly served as an ancestor to all later hominids, says Kimbel, who directs A. afarensis excavations in Ethiopia.

Leakey and her colleagues unearthed the new skull and associated fossil frag- ments in August 1999 at a site located just

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ancient animals whose remains have been found at the Kenyan site appear to have been suited to a wetter, more vegetated habitat than that frequented

J by Lucy’s kind, the researchers say.

The new find’s surprising mix of anatomical features indicates that some parts of the skull can change in striking ways without affecting the shape of near- by areas, Leakey’s group adds. For exam- ple, K. platyops combined a forwardly positioned cheekbone with small cheek teeth. However, Paranthropus-a ho- minid genus that lived from around 2 million to 1 million years ago-blended a comparable cheek bone with large, peg- like molars.

“Many of the skeletal features of early hominids may have been acquired piece- meal, not as large anatomical complex- es,” Kimbel proposes.

Another approach holds that the evo- lution of crucial parts of the skeleton in various hominids triggered many other bony alterations (SN: 11/25/00, p. 346).

The position of K. platyops in the hu- man evolutionary tree will remain uncer- tain for some time, according to Daniel E. Lieberman of George Washington Univer- sity in Washington, D.C. “There’s no sim- ple way to figure out who’s related to whom,” he says. -B. Bower

New nanosize detector picks through DNA Researchers have developed a new between two volumes of a salt solution

technology for rapidly distinguishing be- and added DNA molecules with a sin- tween almost identical DNA molecules. gle, known base sequence to one side.

The highly sensitive device, called a Applying a voltage across the mem- nanopore detector, might eventually brane drew hairpin DNA molecules into be able to sort through DNA and iden- the pore one at a time. Initially, each tify a small variation that predisposes molecule got stuck in the pore, which a person to some disease. The tech- narrows from 2.5 nanometers in diame- nique might even permit DNA sequenc- ter to 1.5 nm. But then the hairpin ing at unprecedented speeds, report spontaneously untwisted into a single Wenonah Vercoutere and her col- strand, thin enough to zip farther into leagues at the University of California, the channel.

cules of so-called hairpin DNA, in Nanopore detector (left) pulls in a hairpin DNA which a single strand doubles molecule, which gets stuck (center). Once it back onto itself to create a tiny uncoils, the molecule can go farther into the loop at one end. narmwing passage (right). A characteristic current

In each molecule, the four change indicates which molecule is in the detector Y

types of nucleotide bases-the chemical units that code for genetic in- formation in DNA-followed a sequence chosen by the researchers. Along the in- tertwined stem of each hairpin, the bases paired up, while the loop at the top con- tained four unpaired bases.

The researchers placed a membrane

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Each DNA molecule created a charac- teristic electrical signal as it blocked the pore and then moved on, says team member David Deamer. The researchers created a computer program that learned these signatures.

“We’re pulling [the molecules] into the

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pore and tasting them,” Deamer says. The computer program can differenti-

ate the DNA molecules in a solution of many different types, adds team member Mark Akeson. “We can tell eight to nine different guys apart in one set,” he says. The device can differentiate between hairpin molecules that vary by as little as one base pair in their stem or one un- paired base in their loop, he adds.

Although scientists have been experi- menting with such detectors for several years, “this is the first time that nanopore technology has demonstrated this kind of resolution,” comments Daniel Branton, whose team at Harvard University also experiments with the technique.

Such sensitivity is an important step toward eventually using nanopore de- tectors to rapidly sequence DNA, says Branton. Researchers should now also work toward building stronger, longer- lasting devices, he says, since the cur- rent structures are relatively delicate.

In the current design, DNA molecules move through the pore too quickly to allow identification of individual bases, says Deamer. The team is looking for ways to slow the hairpin molecules, he says. --J. Gorman

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Study reveals male link to preeclampsia Women who suffer a pregnancy com-

plication called preeclampsia seem to pass on the tendency to their daughters, research shows. A new study suggests that women who bear sons after having preeclampsia also convey some risk to their future daughters-in-law.

This seemingly odd conclusion stems from research at the University of Utah School of Medicine in Salt Lake City. There, scientists have found that men who were born of mothers with preeclampsia are twice as likely to father children through preeclamptic pregnancies as are men born of normal pregnancies.

A man can pass genetic flaws on to his offspring at conception. It appears that some still-unidentified genetic traits can contribute to preeclampsia in his mate, says study coauthor M. Sean Esplin, an obstetrician at Utah. The work reinforces the notion that the condition-at least some of the time-is triggered by charac- teristics of the fetus, not the mother, he says. The study appears in the March 22 NEW ENGLAND JOURNAL OF MEDICINE.

“This is a very interesting and poten- tially useful study that provides evi-

dence that males contribute to preeclampsia,” says James L. Mills, a pediatrician and epidemiologist at the National Institute of Child Health and Hu- man Development in Bethesda, Md. By reviewing the medical records of three generations within families, he says, the researchers avoid the imprecision of personal recall.

Preeclampsia, which usually strikes in the third trimester of a pregnancy, is marked by high blood pressure, swelling, and protein in the urine. It sometimes leads to eclampsia, which can include seizures, coma, and death. For preeclamp sia, physicians often prescribe rest and blood pressure medication. In severe cas- es, they will deliver the baby by cesarean section to end the pregnancy, which halts the preeclampsia.

To find a hereditary link between par- ents and offspring, the researchers iden- tified 298 men and 237 women in Utah born of mothers who had preeclampsia. The scientists matched these people with a control group of 596 men and 474 women born of normal pregnancies.

Next, they compared offspring of the men and women in each group. Only 1.3 percent of children in the male control group were born of preeclamptic preg- nancies, compared with 2.7 percent of children fathered by men born of preeclamptic women, the researchers report. Nearly 5 percent of pregnancies among women born of preeclamptic mothers were themselves plagued by preeclampsia, more than triple the control group’s rate. That finding con- firms earlier studies.

Researchers have sought the source of preeclampsia for more than 100 years without success. Some studies have hint- ed that certain genes could play a role, particularly if both parents carry the same recessive gene, Esplin says.

Other research suggests that several gene variations could combine to predis- pose a person to preeclampsia, says Carl A. Hubel, a physiologist at Magee- Womens Research Institute at the Uni- versity of Pittsburgh Medical Center.

Preeclampsia is most common in first pregnancies, with less risk in later preg- nancies. However, when a women changes partners, the risk rises again, says Mills. Also, a 1998 study in Norway tracked men whose mates had preeclamp tic pregnancies. Even with a new partner, these men had nearly twice the average chance of fathering a child through a preeclamptic pregnancy. These factors are all consistent with a paternal link to preeclampsia, Mills says.

Preeclampsia affects about 1 in 20 pregnancies and appears more common in black women than white. The low inci- dences in the new study reflect the large- ly white Utah population. -N Seppa

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