Fewer Genes to Make a Person

In another blow to humanity's collective ego, it turns out that it takes far fewer genes than scientists thought to make a person.

When geneticists started mapping the human genetic blueprint, known as the genome, about a decade ago, they estimated that it took perhaps 100,000 genes to make a human being. But since a draft of the genome was completed, that number has been steadily dropping. A recent estimate had put the number at about 35,000.

But the number fell even lower last week, when the International Human Genome Sequencing Consortium, a collaboration of scientists from 20 institutions in the United States, Europe and Asia, published a final version of the map of the 3 billion building blocks that make up the entire genetic code in the Oct. 21 issue of Nature. The final version reduced the estimated number of genes that actually carry instructions for the production of proteins, the fundamental components of life, to between 20,000 and 25,000. That is about the same number as for a lowly roundworm often studied by scientists called Caenorhabditis elegans and a small flowering plant in the mustard family called arabidopsis.

"This new analysis reduces the number even further and provides us with the clearest picture yet of our genome," said Francis S. Collins, director of the National Human Genome Research Institute at the National Institutes of Health.

The number makes it clear that it is not simply the number of genes that leads to the complexity of an organism, but what those genes do and how they interact, scientists said.

"The availability of the highly accurate genome sequence in free public databases enables researchers around the world to conduct even more precise studies of our genetic instruction book and how it influences health and disease," Collins said.

-- Rob Stein

Breast Milk's Staying Power

Human breast milk that is frozen or stored for longer than 48 hours loses a significant amount of its antioxidant content, making it less able to help infants fight off free radicals that play a role in allowing infections and other diseases.

Previous studies of the staying power of mother's milk had found that many of its benefits are not affected by refrigeration, and that bacteriological, nutritional and immunological advantages for infants continue after the milk is expressed and stored. However, researchers at the Robert Wood Johnson Medical School found that the combination of vitamins, uric acid, carotenoids and enzymes that seems to make breast milk rich in antioxidants is degraded with storage.

The study found that the same decline did not occur with formula. But even after it has been refrigerated for seven days, breast milk contains more antioxidant capacity than infant formula.

The antioxidant content of mother's milk has been linked to reduced levels of gastrointestinal and lung disease in breast-fed infants, both term and pre-term, when compared with those fed infant formula. Antioxidant capacity is a measure of how well the blood can neutralize the oxidizing effects of free radicals.

The new study, published in the Archives of Disease in Childhood, sampled milk from eight mothers who delivered prematurely and eight who delivered at term. The antioxidant capacities of the two samples were the same.

-- Marc Kaufman

Hurricanes and Global Warming

Several researchers now say that this year's intense hurricane season shows that global warming is disrupting weather patterns more drastically than scientists had previously believed.

National Atmospheric and Oceanic Administration research scientist Thomas R. Knutson and Old Dominion University professor Robert E. Tuleya published a paper last month saying that mathematical models indicate hurricanes will be slightly more intense a century from now. Last week, Paul R. Epstein, associate director of the Center for Health and the Global Environment at Harvard Medical School, said we are seeing what Knutson and Tuleya "are predicting 80 years out."

In addition to recent hurricanes, he said, other intense weather disruptions include Europe's heat wave in 2003, the six feet of rain in three days that accompanied Hurricane Mitch in 1998 and the five feet of rain Haiti experienced over 36 hours in May.

Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research, said rising sea surface temperatures are creating more water vapor in the lower atmosphere, which is connected to more severe weather events.

"There is a much larger pattern going on," Trenberth said. "This is a real risk, and it's something we're going to have to deal with as we move into the future."

But University of Virginia professor and Cato Institute senior fellow Patrick Michaels questioned the analysis, saying that over the past 100 years, rising sea surface temperatures have accounted for just 10 percent of hurricane variability.

"The relationship between sea surface temperatures and hurricane activity in the Atlantic is not as strong as one might initially think," he said.

-- Juliet Eilperin

Humans may have more in common with a roundworm than they had thought.