It is true that “organisms do not act according to ethical fitnessism”, but that is not what I stated. What is true is that organisms tend to act according to ethical fitnessism, which is what I stated. It is true by definition. I believe that a strong argument for a moral theory is that it is being practiced more than other moral theories.
As a consequentialist it is hard to predict which actions in fact will maximize the intrinsic value and in retrospect a behaviour that might have been seen as favourable at the time can have been a huge mistake in the long run and such behaviour will not be favoured by natural selection. Natural selection might seem short-sighted but it is not.
What is true is that organisms tend to act according to ethical fitnessism, which is what I stated. It is true by definition.
This might be a language issue, but no, this is not true because it flips the causation.
Saying that A (organisms) tend to act according to B (ethical fitnessism) implies that B came first and is the cause of A's behaviour. This is not true in this case. Here A's behaviour came first and you just stuck a label on it which says "B".
I noticed that there has been some earlier discussion about Sam Harris’s Moral Landscape Challenge here at LW. As a writer on the Swedish politico-philosophical blog The Inverted Fable of Reality, I would like to share a response to the challenge, written by our main contributor, which I believe is interesting to read even if you are not familiar with The Moral Landscape or its content. See this link for the response and a short explanation of the challenge.
The response takes a different approach to most responses to the challenge. It is divided into four parts and starts by asking which ethic is most compatible with science and reality and finally tries to answer this question.