U.K. researchers say a genetic "mistake" 500 million years ago triggered an evolutionary pathway that eventually led to humans and many other animals.

It happened when a spineless creature on the ocean floor experienced two successive doublings in the amount of its DNA, a major genomic event that eventually led to the evolution of humans and other vertebrates, the researchers said.

The results have been both good and bad, researchers said. Good because the DNA doublings boosted cellular communication so that our body cells are better at integrating information; bad because breakdowns in that communication, traced back to the same genome duplications, can cause diabetes, cancer and neurological disorders.

"Organisms that reproduce sexually usually have two copies of their entire genome, one inherited from each of the two parents," researcher Carol MacKintosh told Discovery News.

"What happened over 500 million years ago is that this process 'went wrong' in an invertebrate animal, which somehow inherited twice the usual number of genes," said MacKintosh, a professor in the College of Life Sciences at the University of Dundee.

"In a later generation, the fault recurred, doubling the number of copies of each gene once again."

"The duplications were not stable, however, and most of the resulting gene duplicates were lost quickly -- long before humans evolved," she said.

But some did survive, MacKintosh and her team said.

They studied several hundred proteins that work in human cells to coordinate responses to growth factors and to the hormone insulin.

A biochemical analysis of the proteins found they date back to the genome duplications 500,000 years ago.