Is it Darwinism as positivism ? if it is ; why ICC regards Darwinism as “the scientific achievements of mankind”
You would have to specify what you mean by "positivism" and why it is antithetical to scientific achievement.
I too don't get what you mean by "positivism" in this respect but in regard to his importance to the ICC specifically, and to the workers' movement generally, the analyses of Charles Darwin and Alfred Russel Wallace, I insist, end up being a profound denunciation of bourgeois society and its capitalist system.
The method that Darwin and Wallace use to reach their revolutionary conclusions - because they accurately describe a pre-historical revolution - is similar to that of Marx and Engels and they certainly come to the same conclusions of that period. And further they show that society, or rather a society way beyond anything that existed in the animal kingdom, was responsible for the advance of mankind. There's nothing deterministic about this analysis which rejects both the ideas of "evolution" on one hand and "the survival of the fittest" on the other. The basis of this advance was the overturning of natural selection which plays such a dominant role in the animal kingdom, and replaced by the, fairly rapid if not instantaneous I imagine, development of a certain consciousness, morality and solidarity.