Elephants have extra copies of a gene that fights tumour cells, which could explain why they rarely develop cancer.

Joshua Schiffman at the University of Utah in Salt Lake City and his colleagues studied elephant white blood cells and found that they have 20 copies of a tumour-suppressor gene called TP53 in their genome — humans and other mammals have only one. The cells also underwent TP53-mediated apoptosis — programmed cell death — more frequently than human cells do when exposed to DNA-damaging radiation. This suggests that elephant cells kill themselves to avoid the risk of uncontrolled growth.

In a separate study, Vincent Lynch at the University of Chicago in Illinois and his co-workers report similar results. They also discovered more than a dozen TP53 copies in two extinct species of mammoth, but just one copy in manatees and in small furry mammals called hyraxes — both close living relatives of elephants. The extra copies may have evolved as the animals in the elephant lineage expanded in size, says the team.

J. Am. Med. Assoc. http://doi.org/772 (2015); Preprint at bioRxiv http://doi.org/773 (2015)