Tick

This explains a lot. Or at least why my shoe laces keep unraveling.

Guardian Unlimited | Life | The final countdown: "The quiet periods in the fossil record where evolution seems to stagnate are a big problem for natural selection: evolution can't just switch on and off. Over 20 years ago the late Stephen Jay Gould suggested internal genetic mechanisms could regulate these quiet evolutionary periods but until now no-one could explain how it would work."