Thus, and because the adaptation to the peculiar conditions on Socorro may even have accelerated not only morphological but also molecular evolution – see also founder effect -, it cannot be said with any certainty whether or not among "Mimus", the Socorro species is a quite recent island offshoot of either of the mainland species. In any case, the three taxa are very close relatives. This serves to show that evolution does not move on at a constant speed; certainly not on a morphological level, and often neither on a molecular level either. Rather, the rate of evolutionary change varies, sometimes considerably, depending on the circumstances and the strength with which natural selection acts upon a founding population.