With all of the recent successes of genetics, it has become commonplace to think of biological patterns as arising from reaction-diffusion mechanisms controlled by genes. However, the crocodile has something to add to this.
Michael Milinkovitch of the University of Geneva and colleagues studied the patterns of crocodile-head scales and found that they are driven by physical processes. As crocodiles grow, their keratinized skin cracks in random ways, with no symmetry between one side of their head and the other – in contrast to what happens with the scales of snakes. So even a crocodile’s genome has no say in how its scales will turn out. They will be distributed by physics with some randomness, rather than by information in genes.