There is a poignant scene deep in this book in which Jeffrey Kluger describes a breaking-and-entering incident at his suburban Baltimore home when he was 7 years old. The intruder turns out to be his father, who — “windblown and looking furious” — has put his fist through a kitchen window to gain entry and has made his way upstairs. There’s shouting, and doors slam.

Kluger’s parents are going through an ugly divorce, following a volatile 11-year marriage, and his father is there to serve his wife with legal papers. When the yelling subsides, his father appears in the doorway of the bedroom Jeffrey shares with his older brother, Steve, and barks, “I love you, boys!” The brothers are paralyzed and speechless. Jeffrey, who has recently developed a passionate interest in nature, reaches for a plastic model he has made of a marsh bird called a hoopoe. In the only act of appeasement he can think of, the 7-year-old asks his father, “Do you like my hoopoe?”

Anyone who has ever experienced a once-hopeful family’s dissolution, from any perspective, has to be moved by this raw emotional narrative. As readers — and as brothers and sisters and fathers and mothers — our hearts go out to Steve and Jeffrey and to their two younger brothers, Garry and Bruce, who are cowering in their own room down the hall. We want them to know they will endure this wrenching storm.

And they do. They have their share of rough strife, which we witness in snatches throughout “The Sibling Effect.” But as we share the travails of Jeffrey and Steve and Garry and Bruce, we also get to witness their deep and primal bond as they are forged into “a loud, messy, brawling, loyal, loving, lasting unit.”

That’s what this volume is about: the unchosen yet powerful intertwined relationships that make up the unit commonly called “sibs.” Our husbands and wives come relatively late into our lives, as do our own children, but siblings are witness to the whole, shared journey. Kluger, a science writer at Time magazine, describes both the ups and downs of the sibling experience, because along with the unique bonds come the hostilities, the favoritism and jealousies, the shifting allegiances and duties as families grow and break up and blend with other families.

"The Sibling Effect: What the Bonds Among Brothers and Sisters Reveal About Us" by Jeffrey Kluger (Riverhead. 3908 pp. $26.95) (Riverhead/Riverhead)

Unhappily, Kluger’s personal narrative is much more compelling than the science writing in “The Sibling Effect.” That’s not entirely the author’s fault. The science itself is thin, lacking in rigor and mostly inconclusive. Sibling relationships are complex and nuanced and varied, perhaps beyond social scientists’ powers of description and analysis.

But Kluger has to share the blame. Where the science is lacking, he substitutes anecdotes and stories and unwarranted leaps of interpretation. Consider the chapter on birth-order effects, which everyone seems to find fascinating: Is the first-born consistently the intellectual superstar of the family? Is the youngest really the wildest? How about all the middle children, like the author himself? Is it true that these siblings are aimless and undirected? The historical anecdotes that Kluger supplies are entertaining, but they are in the end just stories. The problem is that no scientist has proven anything firm about these effects. There are as many exceptions as there are rules.

The frustrating thing is that Kluger knows this, and says so elsewhere, then forges ahead with wild over-interpretations of the data. In a particularly egregious example, he refers (without citation) to studies in the Philippines which show that later-born siblings tend to be shorter and weigh less than earlier-born sibs. It’s impossible to assess this study without more information, but let’s assume it’s true, and not just for Filipinos. This still does not support this dizzying leap of logic: “Think the slight height advantage of Peyton Manning, the six-foot five-inch quarterback of the Indianapolis Colts, has over Eli, his six-four little brother, who plays the same position for the New York Giants, doesn’t help when they’re trying to throw over the outstretched arms of a leaping lineman? The brothers’ lifetime stats certainly say it does.” Certainly? Really? How did he possibly get from here to there? There are so many flaws in this reasoning — and so many variables ignored — that it’s hard to know where to begin. And this is not the only example of bad science writing here.

This is more than a quibble, but I want to end on a positive note, because I came away liking the authorial voice in this very personal book. Kluger comes across as honest and vulnerable and caring toward his brothers, Steve, Garry and Bruce. I’m glad they still gather at Joe Allen’s bar in New York when they can, because it’s evidence of what we want to believe — that sibling bonds are special and enduring and a source of strength in our untidy lives.

Wray Herbert ’s book, “On Second Thought: Outsmarting Your Mind’s Hard-Wired Habits,” has just been published in paperback.


Brothers, Sisters, and the Bonds That Define Us

By Jeffrey Kluger

Riverhead. 308 pp. $26.95