Evolution of the Moral Code
"Morality is the herding instinct of the individual." -Nietzsche
Within the depths of your imagination, two tribes exist. Peaceful hunter-gatherers, they are exactly equal in every respect. All of the variables in their environment are the same or cancel each other out. Their birth and death rates coincide exactly, their resources and location are so similar that they could be the same tribe.
They remain in this state of equality, completely unaware of each others' existence, until one day a fight erupts in both tribes at the same time which heats to the point where one member of the tribe kills another in anger. Amidst this, something unusual happens: for the first time, a split occurs in the behavior of the tribes. The first tribe frowns upon the behavior, convenes a meeting of tribal elders, and decides to punish the individual. The punishment is severe and public, the individual justly reprimanded for his heinous crime.
In the second tribe, the action is seen as natural. The argument exploded into anger, a perfectly natural emotion, and escalated to the point where it was a life-or-death situation. No punishment is handed down, and the tribe continues to live.
As time passes, the tribe which punished the murder sees few further murders, instead keeping its strict standard and severely punishing any such transgression. The looser tribe sees more murders, as it is perfectly accepted, a part of their moral code. Or rather, an accepted standard not mentioned in their moral code. Time passes. The difference does not cause the end or severe decline of either tribe.
At some point, the tribes become aware of each other, and find it necessary for the purposes of this illustration to go to war. The war is bloody and final, a matter of extermination of one or both tribes. Who wins?
The tribe which did not punish the murder has fewer numbers. The members of the tribe may distrust each other slightly out of fear, and therefore not work as efficiently as a team. For any number of reasons related to the higher rate of murders, the strict tribe, which punished the murders, would come out the victor in the war, destroying or assimilating the other tribe.
The same would likely be true if the crime had been theft, for many of the same reasons. Theft breeds distrust and may eventually lead to murder. Certain actions lead to anger, these action all lead to weakening within the structure of the tribe. Certainly, these negative actions may not be enough to threaten the survival of the tribe against the elements of its surroundings, but it does make it weaker than otherwise comparable tribes. In some cases the tribe may be stronger in other respects due to surroundings, but statistics would hold that the same could be true for any other tribe. The realism of the previous example is shaky at best, but on the whole, about as many situational things could happen to either tribe, so it is useful to...