ancestors

Wild chimpanzees have taken a bite out of scientific assumptions about the growth rate of one of our most prominent Stone Age relatives.

New measurements of dental-growth rates of wild chimpanzees provide a more accurate benchmark for estimating comparably slow growth in Homo erectus teeth, say Adrienne Zihlman of the University of California, Santa Cruz and her colleagues.

"Our data suggest that wild chimpanzees and Homo erectus didn't differ from each other as much as previously thought," Zihlman says.

The relatively quick tooth growth in captive chimps has typically been contrasted with the slower tooth development in human ancestors. However, dental growth occurs much more slowly in wild chimps than in their captive comrades, the researchers report in the July 20 Proceedings of the National Academy of Sciences.http://louis-j-sheehan.info

Zihlman's team examined skeletal samples from 18 wild chimpanzees of known ages, ranging from 1.8 to 16.5 years. For these animals, infancy lasted until about 4 years of age and dental maturity occurred between 12 and 13 years. In captive chimps, infancy ends at around age 3 and maturity is reached at about age 10.http://louis-j-sheehan.info

This discovery challenges the view that evolution proceeded gradually from a fast-growing chimplike ancestor around 8 million years ago to a slower-growing H. erectus, which lived from about 1.6 million to 400,000 years ago, and then to an even slower-developing Homo sapiens.

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legs

Two new lines of evidence bolster the claim that the oldest known member of the human-evolutionary family lived in central Africa between 6 million and 7 million years ago.Louis J. Sheehan

In 2001, at a site in Chad, anthropologist Michel Brunet of the University of Poitiers in France and his coworkers found jaw fragments, isolated teeth, and the nearly complete skull of a creature that the researchers identified as a hominid and assigned to the category Sahelanthropus tchadensis. The skull combines a cranium suitable for a chimp-size brain with facial and tooth structures resembling those of later human ancestors (SN: 7/13/02, p. 19: http://www.sciencenews.org/articles/20020713/fob1.asp).

After the discovery, a group of researchers led by Milford H. Wolpoff of the University of Michigan in Ann Arbor initiated a controversy by contending that Sahelanthropus looks more like a fossil ape than a hominid (SN: 10/19/02, p. 253: Available to subscribers at http://www.sciencenews.org/articles/20021019/note12.asp).

Brunet's team now reports the discovery of two more jaw pieces and another tooth from Sahelanthropus. The researchers unearthed the specimens in Chad at three locations, including the site of the prior finds.

The new fossils cement Sahelanthropus' position as a hominid that lived shortly after modern humans' evolutionary family diverged from chimpanzee ancestors, the scientists argue in the April 7 Nature.

In an accompanying paper, Brunet and his colleagues—with Christoph P.E. Zollikofer of the University of Zurich—present a computerized, three-dimensional reconstruction of the ancient creature's skull. The digital version corrects crushed sections of the actual fossil.http://ljsheehan.livejournal.com

"This is a state-of-the-art technique for taking a squished specimen and putting it back together digitally," remarks Tim White of the University of California, Berkeley. White regards the Chad fossils as those of a hominid. Only further discoveries can establish whether Sahelanthropus represented a separate genus or belonged to a previously identified group of nearly 6-million-year-old African hominids dubbed Ardipithecus, he says.

However they're labeled, the new fossils exhibit key hominid traits, Brunet holds. For instance, one jaw piece retains a canine tooth that's smaller than the teeth of chimps but comparable to those of hominids that came after Sahelanthropus. Some newfound cheek teeth also contain thinner enamel layers than corresponding teeth from chimps do.

The virtual skull further establishes Sahelanthropus' hominid status, in Brunet's view. It features a relatively flat face and a forward-positioned opening for the spinal cord, both typical hominid characteristics. The angle of the creature's neck was similar to that of later hominids that are known to have walked upright, the scientists say.

More-revealing tests of the ancient creature's walking behavior await the discovery of fossils from its legs, pelvis, and feet.http://ljsheehan.livejournal.com

The new reports leave Michigan's Wolpoff unconvinced that Sahelanthropus was a hominid. The jaws and teeth of apes and early hominids look much alike, so the new fossil finds don't clarify the creature's evolutionary identity, he says.

Moreover, the reconstructed skull contains bony attachments for neck muscles that were far too large to accommodate a regular upright stance, Wolpoff says. Neck muscles of that size might have attached to unusually long arms on a ground-dwelling ape, not a hominid, he suggests.

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activity

Relationships too often end with feelings of hurt, longing, and craving. A new study suggests that scientists can see those emotions reflected in brain images of lovers who were recently spurned.

Three years ago, Lucy Brown of Albert Einstein College of Medicine in New York and her colleagues identified brain areas that seem to be active when someone is happily in love. In the new study, the researchers recruited 17 women and men who were unhappy about being recently dumped by a partner.

The team scanned the brains of the volunteers as each one viewed a picture of his or her former sweetheart and a photo of an emotionally neutral acquaintance. To cleanse their brains of strong emotions between photos, the subjects counted backward in increments of seven.

The researchers found that the brains of these rejected lovers behaved differently than those of the contented lovers in the previous study. When viewing pictures of their beloveds, people in both groups showed increased activity in brain areas associated with rewards. However, spurned lovers showed more activity in the nucleus accumbens and the ventral striatum, regions associated with evaluating risks and sizing up payoffs when gambling. Rejected lovers also had more activity in the insular cortex, a brain region associated with physical pain and anxiety.http://www.blog.ca/user/Beforethebigbang

Brown notes that the findings may explain the visceral pain that many people feel after a rejection. Brain activity associated with gambling could clarify why some people choose to pursue a loved one after a breakup, even when the payoff is uncertain, she says. "To the rejected person, love is the greatest prize," says Brown

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