I recently read about a tribe in my Antropology class (can't remember the name, but I better find it soon for the exam), anyway, they have a very strict taboo against sex the first year after having a baby. They would consider sex before that year was up as shocking and immoral. Why?
Well they eat an very low protein diet. Infants really need protien their first 2 years to help their survival. So in this groups history they found that when babies were born too close and weaned too early, they often died. They didn't understand about protein. They didn't have birth control. So the natural option became to simply not have sex for one year after giving birth. This spaced the children and gave them a much better chance at survival.
Their morals are based on their diet! With globalization, they may come to learn about protein and supplement their diets. They may start using modern birth control methods and space their children that way. Will the taboo disappear? Probably not right away. So these people may for years to come consider sex within a year of birth to be immoral, even though the original reason for practicing abstinence is long gone. That will be their moral code. Maybe they would think the punishment for breaking the taboo was dead children.
NC