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One can argue for moral nihilism by claiming that all of our fundamental moral beliefs are explained by the theory of evolution (e.g. early human tribe of liars more likely to fight amongst each other than a more honest tribe, so honest tribe will survive and pass down honest genes), concluding that there exist no objective moral properties.

What are some objections to this kind of argument?

  • I object to your argument on the grounds that you're asking this question, thereby proving that human thought is capable of transcending our amoral inate and inherited impulses. – Richard May 9 '17 at 8:50
  • Responses are mostly defensive along the "it can still be true" lines:"Even if it is granted that crude versions of our concepts of fairness or guilt originated through evolutionary processes in our hominin ancestors, independently of any connection to moral truths, it remains possible that through cultural evolution we have developed refined conceptions of fairness or guilt", see SEP survey. But you are confusing rejection of moral realism with moral nihilism, morality need not be "objective" to be morality. – Conifold May 10 '17 at 1:07
  • you'll find the this book interesting- "Liars and Outliers: Enabling the Trust that Society Needs to Thrive" by Bruce Schneier. Also, I think you need to be more exact in your terminology. There is natural - biological - evolution and there is cultural evolution. – Swami Vishwananda May 10 '17 at 5:24
  • I agree with Conifold, you need to decide if you really are referring to rejection of moral realism (which it sounds like you are), or actually trying to make an argument for moral nihilism by reference to evolution. If the latter, some explanation of how you made that link or what makes you think there might be one might help. – Isaacson May 10 '17 at 6:15
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The sorts of arguments you refer to have come to be known as evolutionary debunking arguments.

One such argument would go something like this:

  1. Our moral beliefs can be fully explained by our evolutionary history.
  2. If so, then moral facts play no role in our moral beliefs.
  3. Therefore, we should be skeptical about the existence of moral facts, or our ability to know them.

The actual arguments are more subtle than this, but I'm using it just to make the issue clearer. How can we respond to such arguments? A comparison with mathematics may be useful. Substitute 'moral' with 'mathematical', and we get:

  1. Our mathematical beliefs can be fully explained by our evolutionary history.
  2. If so, then mathematical facts play no role in our mathematical beliefs.
  3. Therefore, we should be skeptical about the existence of mathematical facts, or our ability to know them.

And we would not want to say that, since skepticism about mathematics is much less plausible than skepticism about morality. So, is this a good objection?

First, it highlights the fact that evolutionary explanations by themselves do not suffice for skepticism (unless you go for a much more global skepticism, which is another issue), which is an important point. Second, it probably does not refute the moral argument. The moral skeptic can reply as follows: there is (at least) one important difference between the case of mathematics and that of morality: in morality we rely heavily on moral intuitions, which are shaped by evolution, whereas in mathematics intuitions play a far less significant role.

(On a related note, there have been attempts to argue for moral realism by imitating indispensability arguments for mathematical realism. E.g. here.)

There are other arguments that try and argue that moral facts somehow do play a role in our beliefs, and so we should remain confident about them. The issue is complex. I suggest that you read the SEP entry on this.

  • Arguments of the form reductio ad absurdum can lead to false conclusions if the wrong assumption is negated. Try substituting 'fairy dust' for 'evolutionary history.' We might, in fact, agree that all mathematical beliefs can, in theory, be fully explained by fairy dust, but it would be incorrect to assume that the fullness of such an explanation establishes fairy dust as being the true source of mathematical certainty. – user3017 May 9 '17 at 15:34
  • The ethico-mathematical analogy seems to work for the argument rather than against it. To believe in existence of mathematical facts is some form of platonism, and that is not very popular nowadays. And if mathematical facts reduce to conventions and/or customs of using concepts and manipulating symbols (a la Wittgenstein and empiricists) and the analogy works then moral objectivism is equally dubious. – Conifold May 9 '17 at 21:42

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