I'm sorry, you are mistaken. Genetic diversity does not lead to stagnation, it leads to evolution.<quoted text>
My point was that genetic diversity leads to stagnation. A species will never evolve and improve upon itself unless it is through isolated small populations. That is how evolution works and how new species come into being.
After one of those mass extinction events there is always a scramble where the surviving species compete to fill all the new ecological niches. Evolution is intelligent design. Nothing random about it. It is all about nature modifying creatures to match the environmental conditions.
Evolution = gene frequency change in gene pools.
Increased genetic diversity = gene frequency change in gene pools.
Yes, it's true that smaller populations are more likely to experience stronger selective forces. But that is not true all the time. The human species has populations of it that are not biologically isolated who are undergoing intense selection pressure (the poor, those with allergies to industrial pollution, those living in areas of poor nutrition, poor calories and high disease).
Humans have massive population numbers, and it turns out we are undergoing rapid evolution in our 1) immune systems and 2) brains.
Smaller populations = increased genetic drift and susceptibility to selection pressure.
Larger populations = increased gene flow, wider diversity of environmental pressures.
Growing populations = increased and increasing genetic variety, wider diversity of environmental pressures
So, yes, a large population is not going to have an adaptive radiation unless it gets separated into isolated populations. However, a large population is going to be experiencing high mutation rates, new genetic variety, and will evolve via gradualism rather than speciation - and this can happy quickly.