Mutations can cause genetic diseases and the vast majority of these have no effective treatment. They raise some difficult questions on the boundaries of science and social science. Selective breeding to "improve" the human race (eugenics) is often regarded as a Victorian relic or Nazi fantasy. Yet, three fetuses with Down syndrome are aborted each day in the UK. Recent research suggests that the average human has around 60 mutations in their DNA; it seems that we are all mutants. A better understanding of the science will help us make better decisions about these difficult issues.