In this meticulously researched and masterfully written book, Pulitzer Prize-winner Deborah Blum examines the history of love through the lens of its strangest unsung hero: a brilliant, fearless, alcoholic psychologist named Harry Frederick Harlow. Pursuing the idea that human affection could be understood, studied, and even measured, Harlow (1905-1981) arrived at his conclusions by conducting research—sometimes beautiful, sometimes horrible—on the primates in his University of Wisconsin laboratory. Paradoxically, his darkest experiments may have the brightest legacy, for by studying neglect and its life-altering consequences, Harlow confirmed love’s central role in shaping not only how we feel but also how we think. His work sparked a psychological revolution. The more children experience affection, he discovered, the more curious they become about the world: love makes people smarter. The biography of both a man and an idea, The Measure of Love is a powerful and at times disturbing narrative that will forever alter our understanding of human relationships.