Cellular clocks help explain why elephants are bigger than mice

Biologists are uncovering how tiny ‘clocks’ in our cells might help govern body size, lifespan and ageing. (Mouse cells seem to run faster than human cells, which tick faster than whale cells.) A wave of research is starting to yield answers for one such timepiece: the ‘segmentation clock’. It helps developing embryos to form repeating body segments, such as vertebrae. Researchers want to understand how differences in developmental pace give rise to organisms with such different bodies and behaviours.