For the microscopic lab worm C. elegans, life equates to just a few short weeks on Earth. The bowhead whale, on the other hand, can live over two hundred years. Why are these lifespans so different? And what does it really mean to ‘age' anyway? Joao Pedro de Magalhaes explains why the pace of aging varies greatly across animals. Lesson by Joao Pedro de Magalhaes, animation by Sharon Colman.