Marxism is both atheistic and Darwinistic. While Stalin did play for a while with an anti-Darwinian theory, he eventually gave up on it and joined the rest of the atheists. Also, the fact that Stalin killed Darwinists for a while is proof of nothing. He killed Communists, he killed Georgians where he was born, he killed those who fought with him, in short he killed anybody. He was an equal-opportunity mass murderer.