The story of "Abraham's Sacrifice" is frequently cited as evidence for why the Bible should not be used as a moral guide. (Not to mention the slightly-less-popular story of Jephthah where the Lord required a father to actually go through with the sacrifice of his child.)
Today, however, I think it would be interesting to look at these stories in a little more context. Like last time, I'm using the word adaptive only to describe things that get one's genes successfully into the next generation -- I don't mean to imply any value judgment.
The thing is this: I understand that human sacrifice was more common in prehistoric societies than modern people realize -- and there was an adaptive reason for it.
Starvation/malnutrition was a major cause of death, if not the major cause of death. Often there would be lean seasons when there won't be enough food in your area for your entire clan/tribe to survive until the next season of plenty. And humans -- being capable of planning for the future -- can identify a dangerously lean season. Ultimately, your clan may have more/healthier survivors if some people make the ultimate sacrifice as soon as you see the crisis coming, rather than having everyone eat what they can until the day they starve to death.
Naturally, this is where religion comes in. Religion is famous for the grand moral re-direction (or cop-out). People can do unethical (even horrific) things -- and feel good about it -- by sincerely believing the simple formula: "it's not my will, it's God's." (See here for a recent example.)
In the case of human sacrifice -- even if it rationally benefits the tribe's survival -- it would be extremely difficult to put it into practice using objective reason alone. Thus, there is adaptive value in believing that the seasons and the plants are controlled by (unseen) intelligent beings that have thoughts and intentions. If you believe that it's the God of the seasons who demands a sacrifice in order to make the plants come into fruit again, then killing one's own child can go from being an unthinkable horror to being a pious duty, perhaps even an honor, that a parent would be willing to carry out.
Anyway, that's just a thought as to why religion may have been adaptive in the past, even if it's not always relevant or helpful in our modern society.