Gömböc

A gömböc is a geometric form with the particularity that it has only two equilibrium states: one stable and one inestable. When you leave the gömböc in the unstable equilibrium, this form will tend by itself tu torn around onto the stable equilibrium.

This geometrical property has been evolutionary selected by some turtoises, adopting turtoises' shells a gömböc-like shape, so if a turtoise with this forms fells into the unstable equilibrium, the shell will be favored to arrange itself to the stable equilibrium. Turtoises with this adaptation may survive more than the ones without, and this characteristic is likely to pass through the offspring, according to Darwin's evolution of species theory.