Scientists have noticed that there are certain periods in the evolution of life on earth where numerous organisms suddenly became very diverse as it something was ushering in evolutionary mutations and developments. Nobody has any clue what sort of genetic or environmental factors could trigger such an event, and i would like to propose what i think could be a large contributing factor.
Instead of trying to fathom what new factors could initiate such change, try and fathom in what ways the removal of existing factors which perhaps were suppressing change could disappear and allow radical diversification to take place.
For example when the vast majority of dinosaurs died our (possibly due to a meteor strike) everything further down in the food chain which survived no longer was constrained by the predatory habits of a dinosaurs which had previously driven large factors of natural selection.
Significant changes in environment in terms of available resources, available plants, predators, prey etc…, could be responsible for destroying finely tuned evolutionary balances and drives which would trigger a new phase of evolution with new selective forces…
Another interesting question would be, assuming that we, humans, will eventually become extinct, how will the subsequent continued evolution be altered because of our presence? How significant of an impact would we will have made on the course of evolution?
Sure, that is why the Cambrian explosion happened, for example. With the dramatic increase in atmospheric oxygen, a whole slew of new niches appeared. Along with those niches, a whole slew of new organisms appeared. That is, until the resolution narrowed as niches were filled and balance reinstated itself.