David Marnajovic wrote:
"I don't completely understand this... anyway, there probably were no suitable empty niches at that time, I'd say."
Well, for a species to turn into another that occupies a different ecological niche, adaptive evolution directed by natural selection is required. But a creature living differently from its ancestors can't evolve, if all of the intermediates aren't favoured by nature. So, I meant that the earliest intermediates didn't spread their alleles better than their fellow beings, and as such a new, different kind of being and a species consisted of many individuals of it couldn't evolve.