I have posted on this before but it is worth a re-read.Many mammals, including elephants and naked mole rats (above) appear to have successful defences against the formation of tumours. These defences may have something to do with the number of times the p53 gene appears in the genome – the more, the better. Humans only have one copy of the gene and have a high risk of developing tumours. Maybe more copies of the gene could be engineered into the human genome? Why not?