The Naturalistic Fallacy is the tendency to think that because something is, it ought to be. The fallacy is that something being natural or part of human nature doesn’t make it right. The rage you’d get filled with thinking of your partner with someone else might be biologically influenced, but that doesn’t justify acting on it. Human morality doesn’t care if nature “allowed” something, only that it doesn’t approve of that behavior now.
The Moralistic Fallacy is the opposite–it says that since something is wrong, it couldn’t possibly be natural. Often it implies that these things are societal creations and “if we would all get along” they would go away. You might find it really sad that people go to war, but obfuscating the influence doesn’t change anything. People lie, cheat and steal everyday and have benefited from the behavior since the beginning of human history. If morality is to be more than words, it has to understand where the resistance comes from.
The Naturalistic Fallacy is a rationalization and the Moralistic is a delusion–both are stupid. And they both need to be avoided.