And this invalidates the theory of evolution in which way?
History changes with human convenience, don't you know. It would be awful if we came from apes. It might even make us totally lawless if we knew. Therefore, we didn't.
Are we in agreement that evil exists and that Stalin embraced it?
If you believe that good and evil exist, that right and wrong are absolutes, and that the spiritual is ultimately far more important than the material; you will be suspicious of ideas which lead to evil.
But I agree, that Stalin's deeds don't invalidate the science of Darwin. It is a huge warning, however, that we should not use science as a basis for morality or put scientific thinking above moral thinking.