Human evolution slower than thought

The genetic code comprises six billion nucleotides, or building blocks of DNA, half of which come from each parent.

Until now, the conventional theory among scientists was that parents each contribute between 100 and 200 changes in these nucleotides.

But the new study says that far fewer changes occur. Each parent hands on 30 on average.

"In principle, evolution is happening a third as slowly as previous thought,"said Philip Awadalla of the University of Montreal, who led the study by the CARTaGENE group.

The discovery came from a painstaking look at the genomes of two families, each comprising a mother, a father and their child.

The study breaks new ground although its sample size is very small.

If confirmed on a wider scale, it will have a bearing on the chronology of evolution. It would change the way we calculate the number of generations that separate Homo sapiens from a primate forebear who is also the ancestor of the apes.

The study also challenged thinking about whether DNA changes are more likely to be handed on by the father or by the mother.