Some chickens appear to be male on one side of the body and female on the other, and researchers writing in Nature this week say they know why.

It was previously thought that sex chromosomes in birds control whether a testis or ovary forms, with sexual traits then being determined by hormones.

The authors of the new study, however, identified differences between male and female cells that control the development of sexual traits. The scientists have named the phenomenon, cell autonomous sex identity (CASI).

The findings may also be relevant to why males and females differ in behavior and in susceptibility to disease.

An analysis in Nature of more than 70,000 galaxies by a team of physicists suggests that the universe – at least up to a distance of 3.5 billion light years from Earth – plays by the rules set out 95 years ago by Albert Einstein in his General Theory of Relativity. But that's not all. They also conclude that the existence of ill-defined 'dark matter' is the most likely explanation for the observation that galaxies and galaxy clusters move as if under the influence of some unseen mass, in addition to the stars astronomers observe.

The 'war on cancer' has led to a reduction in the rate of cancer deaths whether measured against baseline rates in 1970 or in 1990, reports a new study by the American Cancer Society.

According to the study, the downturn in cancer deaths since 1990 is due mostly to reductions in tobacco use, increased screening allowing early detection of several cancers, and modest to large improvements in treatment for specific cancers. The study was published today in PLoS One.

Researchers used nationwide cancer mortality data for the years 1970 through 2006 from the SEER*Stat database, which defines major cancer sites consistently over time in order to facilitate reporting of long term mortality trends.

Spring training is just getting underway for Major League Baseball, and that means it's time for Bruce Bukiet, associate professor of Mathematics at the New Jersey Institute of Technology, to make his annual predictions about the outcome of the season.

Bukiet bases his predictions on a mathematical model he developed in 2000. His model computes the probability of a team winning a game against another team with given hitters, bench, starting pitcher, relievers and home field advantage. For this season, he incorporated a more realistic runner advancement model into the algorithm. Operations Research published Bukiet's mathematical model several years ago.

Researchers studying populations of numerous moth and butterfly species across Papua New Guinea have developed a new technique to study the spread and diet of insect pests--DNA barcoding, which involves the identification of species from a short DNA sequence.

DNA barcodes showed that migratory patterns and caterpillar diets are very dynamic. In one case, a tiny moth that is distributed from Taiwan to Australia, had recently crossed thousands of miles of Pacific Ocean.

The research is detailed in this week's edition of PNAS.

Sonic hedgehog, a gene that plays a crucial rule in the positioning and growth of limbs, fingers and toes, has been found in the ectoderm - the cell layer that gives rise to the skin - in the embryos of developing mice. The gene was previously thought to be exclusively present in the cell layer that builds bone and muscle, called the mesoderm.

The discovery, detailed in PNAS, suggests that Sonic hedgehog's role in the growth of appendages is far more complex than originally thought. Developmental biologists may have to rethink established theories about how limbs are patterned in vertebrates — an effort that could provide insight into human birth defects.