Q. In your case, you stayed close.
A. We do remain very close. And that's not to say it's remotely ideal. But the relationships remain extraordinarily powerful.
Q. What have you learned from your interactions with your half-siblings and stepsiblings?
A. My stepsiblings were an unfortunate aberration. The relationship was so deeply dysfunctional between the two parents [Kluger's mother and his stepfather] and the time we all had in each other's company was so brief. When their marriage ended, after 15 months, our relationships with those kids pretty much ended. One of the unfortunate things I learned is that those stepsibling relationships are so easily destructible — and what a waste that was.
Q. But your relationships with your father's son and daughter from his second marriage turned out better.
A. We overcame so much adversity. I didn't really know them at all till they were in their mid-20s and I was in my mid-30s. We were so hostile to their mother; she was so hostile to us; we were so deeply resentful that they had gotten a reasonably good upbringing from our father. All of that spelled almost certain hopelessness for those relationships. And the fact that we made so much of the relationships since then — that was entirely improbable. The real love that's developed in 20 years has really taken us by surprise.
Q. What is the value of sibling relationships in adulthood?
A. Siblings can be sources of real physical and mental health for one another in ways that we didn't always fully appreciate. We all thrive more when we're part of a supportive social network, when there's somebody double-checking on us, making us accountable. We also stay more alert emotionally. All of these things are making siblings more valuable to each other as life spans extend.
Q. Yet stresses also arise over issues such as aging parents and inheritance. Do you have any advice in these areas?
A. When it comes to caring for aging parents, to the degree you can do it, the best approach is what's in the best interest of the parents. In terms of inheritance, the gold standard is, what will it take to make everybody feel reasonably whole?
Q. What messages would you like readers to take from the book?
A. There are two things. Siblings are not the sine qua non of a happy life. But having siblings and not making the most of them is like having 1,000 acres of incredibly fertile farm land and never planting a single seed.
Q. The other?
A. Never assume your relationship is irreparable because, first of all, your life circumstances may change. Or [a relationship may improve] simply because you make an effort. The power of a sibling who knows everything about you, who knows the family you grew up in, who carries half your genes — there's nothing quite like that.
Julia M. Klein is a cultural reporter and critic in Philadelphia and a contributing editor at Columbia Journalism Review.