Every time a cell divides, there is a chance for a mutation (mistake) to occur in the DNA - the substance that carries genetic information in all living organisms. These mutations can lead to cancer.
If all cells have a similar chance of developing cancer-causing mutations, then very large and long-lived animals with more cells undergoing more cell divisions should develop cancer at a higher rate than smaller, short-lived animals with fewer cells dividing over less time.
But in 1977, Sir Richard Peto noted that humans develop cancer at a rate similar to mice. This is despite