Old Age a Boon to Human Race

Humanity may have its grandparents to thank for enabling it to make a big jump toward modernity. A new study has found that it wasn't until people started living to old age that humans gained a competitive advantage to ensure their evolutionary success.

Rachel Caspari of the University of Michigan at Ann Arbor and Sang-Hee Lee of the University of California at Riverside analyzed more than 750 fossilized teeth from successive periods in early human history to see whether there was a relationship between longevity and evolution.

The researchers found that the ratio of old to young individuals increased steadily until the Upper Paleolithic period, about 30,000 years ago. At that point there was a dramatic jump in longevity -- the number of people surviving to older age more than quadrupled, the researchers found. That corresponds with a sudden explosion in more modern behavior.

"We believe this trend contributed importantly to population expansions and cultural innovations that are associated with modernity," the researchers wrote last week in the Proceedings of the National Academy of Sciences.

Part of the reason, the researchers speculated, is that there were more grandparents to help care for children, increasing survival rates and freeing adults to explore other activities and pass on knowledge to new generations.

"There has been a lot of speculation about what gave modern humans their evolutionary advantage," Caspari wrote. "This research provides a simple explanation for which there is now concrete evidence: modern humans were older and wiser."

-- Rob Stein

Find Disproves Bird's Demise

A team of field biologists has sighted the Cozumel thrasher, a bird not seen in nearly a decade that many thought had gone extinct, the American Bird Conservancy and Conservation International announced Friday. Its rediscovery last month makes it the single most threatened bird in Mexico.

The thrasher, a bird found only on the island of Cozumel off Mexico's Yucatan Peninsula, suffered a serious decline after Hurricane Gilbert ripped through the island in 1988. While increasingly rare, it continued to be sighted occasionally until 1995, the year Hurricane Roxanne tore through Cozumel.

As many as 10,000 Cozumel thrashers once lived on the island, scientists said.

Past expeditions that sought to spot the thrasher failed, but last month a team of biologists working with Villanova University and the Mexican counterpart of the Island Endemics Institute spotted a single bird, proving it was not extinct.

The thrasher is similar to a mockingbird, a medium-size brown-and-white bird with a long, curved bill. Its song is described as "a complex scratchy warbling," said the two conservation groups.

"The rediscovery of the Cozumel Thrasher is a reminder of two key things: the importance of tropical islands for biodiversity conservation, and the importance of never giving up on a species, no matter how rare," said Russell Mittermeier, Conservation International's president.

-- Juliet Eilperin

Smoking Out New Plant Life

The seeds of many trees, flowers and other plants germinate especially well after exposure to smoke -- a natural mechanism for ensuring rapid botanical recovery after a forest or prairie fire.

Scientists have been in the dark, however, about what it is in smoke that makes these seeds wake up.

Now Gavin Flematti of the University of Western Australia and his colleagues have identified at least one such compound.

The team set fire to filter paper -- which is made primarily of cellulose, the main ingredient in plants -- and extracted various chemical compounds from the smoke. Then they tested the ability of those compounds to enhance the germination rates of seeds from two Australian plants: Conostylis aculeata, a yellow wildflower, and Stylidium affine, or Queen trigger plant, which bears delicate four-petaled, purple-pink flowers.

They found that one compound in particular, a chemical in the butenolide family that remains nameless but whose structure the team was able to identify, was the key to seed germination in smoke-sensitive plants. When they synthesized the chemical from scratch, it worked as well -- not only on the Australian plants, but also on smoke-sensitive plants from North America and South Africa.

The chemical fulfills all the ecological requirements one would expect, the team reports in the July 8 online version of the journal Science. It is stable at temperatures as high as 244 degrees Fahrenheit, for example, and it is soluble in water, so it can soak into seeds.

The chemical could become a useful tool for ecologists seeking to speed restoration of environments denuded by agriculture, mining or other disturbances, the team concludes. Next up are studies to see how it works.

-- Rick Weiss

The Cozumel thrasher, indigenous to Mexico, was thought to be extinct, but one has been sighted.