They thought that non-Aryans were inferior, specially Jews. They thought that only the strongest of the race will survive and others will perish. They thought that for Aryans, it was necessary to kill all non-Aryans. This concept was borrowed from the scientific theory that says something like this about species of animals. It is important to note that the theory never mentions "human races". They misunderstood the theory (or acted like they misunderstood the theory). They thought that Aryans were the best "race".
