Digest this

cellulose, a carbohydrate, is a common constituent of all plants. Despite its widespread prevalence, most animals are unable to directly digest it in their own stomachs, because they lack a key gene to enable them to do so. Now, a study conducted in the uk has found genes that can break down cellulose are far more common among animals than believed. Angus Davison of the University of Nottingham and Mark Blaxter at the University of Edinburgh have jointly identified such genes in several creatures including earthworms, sea urchins, lobsters and bees.

Until now, only a tiny number of animals -- termites, a type of sea mollusk called abalone and sea squirts -- have been known to possess the gene -- called a cellulase gene -- that allows them to digest cellulose. Instead, scientists have believed for decades that most animals rely on bacteria living in their gut to break down the cellulose so it can be converted into 'fuel' for the body. Humans fall into this category.

"We found that not only are cellulases common and widespread in animals, but they can also be traced back to the last common ancestor of all animals -- including Homo sapiens -- more than 600 million years ago," says Davison, who works in the university's Institute of Genetics. The study was recently published online in Molecular Biology and Evolution (Vol 22, No 2). "Cellulases are not rare at all -- and they have not been acquired from bacteria," he adds.

The findings suggest the distant ancestors of modern humans were also able to break down cellulose. But later, we mysteriously lost the ability to do so.

The surprising findings of the study could mean a radical overhaul for much current scientific thinking about cellulose. Davison looked through the genetic data on hundreds of species in search of cellulase genes. He then traced the evolutionary history of those creatures to show that the genes must have originally evolved in one of the earliest animal species.