The Elephant and the Spandrel

Comparative oncology has made great strides in identifying patterns of cancer prevalence and risk across the tree of life. Such studies have often centered on elucidating the evolution of cancer suppression mechanisms, especially in large and/or long-lived animals such as elephants, in which cancer risk is assumed to exert a strong selective pressure. There is a worry, however, that we are overinterpreting these conclusions, as the deep evolutionary origins of these mechanisms and their involvement in cancer-unrelated functions suggest that the preeminent functions of the identified mechanisms may be unrelated to cancer. Instead, cancer suppression may be an evolutionary byproduct, or “spandrel”, of selection acting on development and somatic maintenance. Here, we highlight the importance of development and somatic maintenance as the underlying axis of natural selection. We argue that by shifting the focus of study from cancer suppression to development and somatic maintenance as the ultimate cause, we can gain a deeper understanding of the evolutionary pressures that shaped the mechanisms responsible for the observed variation in cancer prevalence across species.