Monday, October 29, 2007

Some Neanderthals Had Red Hair

Neanderthals, those beetle-browed cousins of ancestral humans who went mysteriously extinct 30,000 years ago, are often depicted as dark-haired and swarthy. Now a study of ancient DNA indicates that at least some of them had fair skin and red hair.

The findings are consistent with the idea that as early humans migrated north from Africa, they had less need for sun-protective dark pigments and may have benefited from light skin's enhanced ability to make vitamin D from sunlight.

Michael Hofreiter of the Max Planck Institute in Leipzig and colleagues isolated DNA from the bones of two Neanderthals whose remains were found in Italy and Spain. They analyzed the MC1R gene, which affects the balance between red-yellow and black-brown pigments in skin. People who inherit a faulty version of the MC1R gene from both parents tend to have pale skin and reddish hair.

The two Neanderthal specimens harbored identical mutations in their MC1R genes, which tests indicated would have led to light skin and red hair if inherited from both parents. And that mutation is different than any ever seen in modern humans, so it appears to have arisen independently from those in today's human lineage.

It is impossible to tell if either of the two Neanderthals inherited the mutated version of MC1R from both parents. But the team's statistical analysis concluded that, since two out of two specimens they looked at had at least one redhead gene each, the odds are that at least 1 percent of Neanderthals did carry mutated copies from both parents and would have had "classically Irish looking red hair and pale skin," they reported last week in the journal Science.

-- Rick Weiss

Red Fall Color Linked to Poor Soil

The splendor of fall color -- just beginning to take hold in the capital region -- may have as much to do with soil composition as with trees themselves.

As the season turns, cooler temperatures and shorter days inhibit production of chlorophyll, the molecule that enables plants to absorb energy from the sun and gives leaves their green color. As the chlorophyll dwindles, the yellow pigments that it masked become apparent to the eye.

But some trees also appear to produce more red pigments, known as anthocyanins, in their leaves when their roots are in soil that is relatively low in nitrogen and other nutrients, according to research to be presented today at the Geological Society of America's annual meeting in Denver.

That finding was made by researcher Emily Habinck, then an undergraduate at the University of North Carolina, who surveyed and analyzed the fall foliage of sweet gum and red maple trees in a nature preserve in Charlotte.

Scientists believe anthocyanins and the red color they produce protect the leaves, delaying their decay and allowing the tree to harvest more nutrients from the leaves before winter. Trees in poor soil therefore would be expected to produce more red leaves.

"For species that don't turn red, they are probably adapted to higher nutrient conditions," said Habinck, now an interpretive ranger at McDowell Mountain Regional Park near Phoenix.

Habinck's findings are in line with research in 2003 by William Hoch, a plant physiologist at Montana State University. Hoch blocked anthocyanin production in red-leafed plants and found that the resulting leaves sent fewer nutrients to the roots.

-- Christopher Lee

Stress Makes Birds More Daring

Birds bred to have higher levels of stress hormones are bolder -- not more scared and retiring -- when faced with a potentially hazardous new situation, a surprising study has found. The "stressed" birds were more willing to visit a feeder in a new cage and to return to it after being startled, than were their more laid-back brethren.

Like other animals -- humans included -- the birds respond to stresses such as the presence of a predator or a new environment by producing a hormone, which in birds is called corticosterone. But some birds have naturally higher levels of the hormone than others, which allowed researchers at the University of Exeter in England to breed and group zebra finches they studied according to whether their levels were relatively high or low.

"It initially seems counterintuitive that birds with higher levels of the stress hormone showed bolder behavior, normally associated with confidence," said Thais Martins, lead author of the study, published last week in the journal Hormones and Behaviour. "However, corticosterone is released to help tackle stress by encouraging the animal to adopt key survival behaviors like seeking food. So on reflection, perhaps it is not surprising that these birds are more likely to explore the environment and look for food."

-- Marc Kaufman

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