Common arguments against morality

An argument commonly used to "prove" that morality was caused by evolution:

1. Evolution caused the human mind.
2. The human mind has moral beliefs. (For example, "Rape is evil")
3. Therefore, evolution caused moral beliefs.

While this argument shows that evolution caused your moral beliefs, it does not follow that moral facts are caused by evolution. Consider this parallel version:

1. Evolution caused the human mind.
2. The human mind has arithmetic beliefs. (For example, 2+2=4)
3. Therefore, evolution caused arithmetic beliefs.

The conclusion is true, but no one believes that arithmetic facts are controlled by evolution. All the argument says is that evolution has allowed us to know about arithmetic facts. The same goes for moral facts.

Notice that the word "evolution" does not really affect the logic of the argument: You could replace the word "evolution" with "mad scientists" or "breeding by the Nazis" or "a random explosion". The point is, we cannot show that the thing which caused the human brain has any power to actually affect the truths believed by the human mind. It can only affect whether the human mind believes them.

Some have used the fact that psychopaths exist to suggest that moral truths don't exist. Again, this seems to me like suggesting that, since there are people ignorant of the ten times table, the ten times table does not exist.

Some have pointed to varying moral beliefs to suggest that moral statements are not objectively true. This is a bit like suggesting that the law of gravity is not objectively true since it is different on the earth and the moon. Suppose both of us are nurses: you believe the green bottle of medicine would cure a patient, and I believe the blue bottle would cure him. Clearly we don't disagree on whether it is right to cure the patient: We only disagree about which methods are effective. That some cultures believe a man should have five wives and other cultures believe he should have only one is not a difference in morality: All cultures believe the man should not have anyone he likes. They merely believe different methods are effective for achieving that aim.


It seems to me that if evolution were able to make you believe whichever moral belief happened to be convenient, it would have done so a lot more than what it has. For example, when I stole my classmates' sweets at school, I never did so because I felt morally obliged to do so. Quite the opposite: I did so despite feeling morally obliged not to. If evolution has the power to make us believe any moral statement, it has not exercised this power as effectively as it could.