Based on the comprehensive picture of the biological role of senescent cells, it seems likely that an evolutionary trend resulting in deletion of incipient cancer cells by ‘gatekeeper’ tumour suppressor functions such as p53/p21 and pRB/p16 [3] would be sufficient to safeguard a species against pathological propagation of somatic mutations – with cancer as a major outcome. The gene discussed is RB1; the disease is cancer.