The role of p53 as a tumour suppressor is generally attributed to its ability to stop the proliferation of precancerous cells by inducing cell-cycle arrest or apoptosis. The relatives and evolutionary predecessors of p53 - p63 and p73 - share the tumour-suppressor activity of p53 to some extent, but also have essential functions in embryonic development and differentiation control. Recent evidence indicates that these ancestral functions in differentiation control contribute to the tumour-suppressor activity that the p53 family is famous for.