Key to Human Complexity Is Not Number of Genes

In a blow to human vanity, researchers now say that people have about the same number of genes as a small flowering plant or a tiny worm. The new estimate is down sharply from just three years ago.

“We [humans] don’t look very impressive in the competition,” said Dr. Francis Collins, co-author of the new analysis by the international group that decoded the human genome.

The new estimate is 20,000 to 25,000 genes, a drop from the 30,000 to 40,000 the same group of scientists estimated in 2001.

By comparison, C. elegans, a worm that is a favorite research subject, has about 19,500 genes. Another lab favorite, a plant in the mustard family called arabidopsis, has about 27,000.

So how can humans be so complex with relatively few genes?

Collins, director of the National Human Genome Research Institute, said that in comparison with simpler organisms, humans benefit more from genes that turn out multiple proteins rather than one, and from complex proteins that do more than one job.

And lots of biological complexity is based not on individual proteins but on combinations, which can create lots of variety from the proteins found in people.

“It’s not just the number of genes that matters,” said another co-author, Eric Lander of the Broad Institute in Cambridge, Mass. “It really is how nature uses these genes.”

The new estimate deals only with genes that tell cells how to make proteins.

The findings were reported in Thursday’s issue of the journal Nature by the International Human Genome Sequencing Consortium, which had determined the sequence of nearly all of the more than 3 billion chemical building blocks that make up the human DNA code.