Right. I think the argument was more along the lines of the Niche Exclusion Principle[1]. Once the existing complex organisms have had time to adapt "perfectly"

Right. I think the argument was more along the lines of the Niche Exclusion Principle[1]. Once the existing complex organisms have had time to adapt "perfectly" and fill "all" of the low-level ecological niches, the barrier to entry becomes dramatically higher. The odds of evolving complexity were already abysmal. The presence of an additional barrier makes it almost impossible, since the new, unoptimized design would have to compete with the established species. It's a debatable argument, with obvious parallels in the startup world. [1] http://en.wikipedia.org/wiki/Competitive_exclusion_principle http://en.wikipedia.org/wiki/Competitive_exclusion_principle In ecology, the competitive exclusion principle is a proposition which states that two species competing for the same resources cannot coexist if other ecological factors are constant. When one species has even the slightest advantage or edge over another, then the one with the advantage will dominate in the long term. One of the two competitors will always overcome the other, leading to either the extinction of this competitor or an evolutionary or behavioral shift towards a different ecological niche. The principle has been paraphrased into the maxim "complete competitors cannot coexist".