Survival of the fittest (or most ethical)?

"Life is flight, and the strongest wins. All civilization does is hide the blood and cover up the hate with pretty words!"
"Your civilization, perhaps. Ours hides nothing. It is all plain . . . We follow one law, only one, the law of human evolution."
"The law of evolution is that the strongest survives!"
"Yes; and the strongest, in the existence of any social species, are those who are most social. In human terms, most ethical. You see, we have neither prey nor enemy, on Anarres. We only have one another. There is no strength to be gained from hurting one another. Only weakness."

- Ursula Le Guin, The Dispossessed, pg 185

I've always enjoyed well written science fiction that explores issues of philosophy, religion, and what it means to be human. Ursula Le Guin's The Dispossessed is a novel about two civilisations: the planet of Urras, a society based on democracy and capitalism, and the planet Anarres, a society that functions successfully without laws or government. The quoted passage above, a debate between two people from each of these worlds, tackles the creationist argument that the theory of evolution teaches that "might makes right" and that the only correct way to behave as human beings is to trample on the weak.

Not only is such an argument an example of the naturalistic fallacy, but as the quote above clearly shows, the fittest are not necessarily those who are the most violent or domineering. As far as I understand, those organisms that are the strongest (or fittest), in the context of evolutionary theory, are those who are the most successful in passing along their genes to the next generation. And what better environment to successfully bear children than in a stable, peaceful society based on a common code of ethics.