A life-changing mistake took place at a Colombian hospital in 1988: two sets of identical twins were switched at birth, splitting up the siblings and sending one of each set to a completely different family as the supposed fraternal twin of another. The error was discovered in 2014, when the boys were 25. In what should be required reading for all who study nature and nurture, Segal (psychology & director, Twin Studies Ctr., California State Univ., Fullerton) and Montoya (associate director of advising, Columbia Univ. Sch. of Social Work) reveal how the boys' families could not have been more different—one, urban, well educated and well connected; the other, hardworking and living in a rural area, where the house lacked electricity and running water. Each mother believed her twins to be fraternal. Lucky for readers, there are many pictures of the twins, parents, siblings, and other relatives, plus charts and maps to help keep track of everyone. The authors delve deeply into the boys' abilities, personalities, religions, goals, and behaviors. There are only seven known cases of identical twins switched at birth, so this research is new and thorough. VERDICT Essential for psychology and sociology students; fascinating for lay readers. [See Prepub Alert, 10/22/17.]—Linda Beck, Indian Valley P.L., Telford, PA