Mutations

By sequencing the complete genomes of a family of four, researchers have estimated the number of new mutations that each parent passed on to the children: about 30. When you consider that the human genome contains around 3 billion base pairs, that's an error rate of about 1 in 50 million. Which is, I would say, remarkably accurate. And it is a lot less than the error rate you would estimate by exposing human DNA to a generation's worth of radiation and chemical assault and counting how many errors creep in. Most of those errors are screened out somewhere in the course of replication and reproduction.