[Retra]

A long time ago, I was trying to imagine how complex structures could evolve out of randomness, I came up with something I called "hinge evolution." Let the relevant behavior of a system be a function of the contact area between the two planes of the hinge, and the genetic variation be represented by the action of hinge. You can vary the hinge angle a lot while only causing minor shifts in the contact area, but if you close the hinge, there will be a giant discontinuous spike in the contact area. So I believed it wasn't absurd to think that things didn't have to evolve in continuous fashion: you could have 'silent' evolution happening in the background, but when certain conditions are met, a major shift in structure could happen all at once.

This article elucidates a much better explanation.