By the numbers, geneticists thought about mutations like this: There are six billion pieces (nucleotides) of genetic information in the genome. Three billion provided by the mother and three billion from the father. Based on evolutionary studies, previous estimates reckoned about 100-200 mutations would be passed on to each child. It was assumed that because the male genome is copied millions of times during the creation of sperm, compared to the tiny number of eggs produced by the female, most of the mutations would be coming from the father. Apparently not.

Research by Philip Awadalla, University of Montreal (Canada) and Matt Hurles, Wellcome Trust Sanger Institute (Cambridge, UK) and published in Nature Science [12 June 2011, paywalled, Variation in genome-wide mutation rates within and between human families], indicates that the actual number of mutations we receive from our parents is about 60 – roughly a third of the original estimate. That means, among other things, that the rate of evolution based on genetically inheritable mutations is much slower than thought.

The research also indicates that the number of mutations provided by the mother and father varies. In one case the father provided 92 percent of the mutations, in another case the mother provided 64 percent. Note, however, that these two cases were the only cases in the study. This significant limitation was imposed by the difficulty and cost of sequencing and sorting the genetic information. While these findings are extremely interesting and point to factors based on family or environment, this study must be considered preliminary to hopefully much larger studies in the future.