Born Together-Reared Apart: The Landmark Minnesota Twin Study

by Nancy L. Segal

Overview

The identical “Jim twins” were raised in separate families and met for the first time at age thirty-nine, only to discover that they both suffered tension headaches, bit their fingernails, smoked Salems, enjoyed woodworking, and vacationed on the same Florida beach. This example of the potential power of genetics captured widespread media attention in 1979 and inspired the Minnesota Study of Twins Reared Apart. This landmark investigation into the nature-nurture debate shook the scientific community by demonstrating, across a number of traits, that twins reared separately are as alike as those raised together.

As a postdoctoral fellow and then as assistant director of the Minnesota Study, Nancy L. Segal provides an eagerly anticipated overview of its scientific contributions and their effect on public consciousness. The study’s evidence of genetic influence on individual differences in traits such as personality (50%) and intelligence (70%) overturned conventional ideas about parenting and teaching. Treating children differently and nurturing their inherent talents suddenly seemed to be a fairer approach than treating them all the same. Findings of genetic influence on physiological characteristics such as cardiac and immunologic function have led to more targeted approaches to disease prevention and treatment. And indications of a stronger genetic influence on male than female homosexuality have furthered debate regarding sexual orientation.

Product Details

ISBN-13:	9780674055469
Publisher:	Harvard University Press
Publication date:	06/18/2012
Pages:	416
Product dimensions:	6.50(w) x 9.30(h) x 1.30(d)

About the Author

Nancy L. Segal is Distinguished Professor in Humanities and Social Sciences and Director of the Twin Studies Center at California State University, Fullerton.

Table of Contents

Introduction 1

1 The Jim Twins (February-March 1979) 17

2 15,000 Questions x 137 Pairs 32

3 Early Findings (1979-1983) 65

4 Sexual Orientation, Cognition, and Medical Traits (1984-1987) 82

5 Pivotal Papers: Personality and IQ (1988 and 1990) 97

6 Job Satisfaction, Cardiac Characteristics, and More (1989-1990) 116

7 Psychopathology and Religiosity (1990) 136

8 Dental Traits, Allergies, and Vocational Interests (1991-1992) 153

9 Creativity, Work Values, and Evolution (1992-1993) 171

10 Family Environments, Happiness, Sensation Seeking, and the MMPI (1994-1997) 195

11 "Larks" and "Owls," Ego Development, and Authoritarianism (1998-2002) 221

12 Twin Relationships, Social Attitudes, and Mental Abilities (2003-2005) 246

13 Sexual Development, Fluctuating Asymmetry, Body Size, and the Structure of Intelligence (2006 and Beyond) 266

14 Questions, Answers, and Twin Studies of the Future 298

Appendix A Funding Sources 329

Appendix B Glossary 333

Notes 339

Acknowledgments 397

Index 401

What People are Saying About This

Matt Ridley

This is a vivid and intimate account of one of the classic episodes in the history of the nature-nurture debate by somebody who was part of the team. The Minnesota Study of Twins Reared Apart made a vital difference, against often entrenched conventional wisdom, to the understanding of human development. Nancy Segal tells the story of the project superbly.
— Matt Ridley, author of Nature via Nurture

Steven Pinker

Twins separated at birth are endlessly fascinating and give us some of the best scientific insights into nature and nurture. No one can tell this story better than Nancy Segal, gifted scientist, raconteur, and wise observer of human nature.
— Steven Pinker, author of The Better Angels of Our Nature

Robert Plomin

Born Together-Reared Apart is a tour-de-force in the history of psychology and twin research. Describing the twins' life stories as well as the scientific data, Segal gives us a compelling account of the findings, implications, and controversies from the world famous Minnesota Study of Twins Reared Apart. The book will be essential for anyone seriously interested in the genetic and environmental influences affecting human health and behavior.
— Robert Plomin, Professor of Behavioral Genetics, King's College London

Editorial Reviews

Segal has provided a thorough history and detailed analysis of the Minnesota Study of Twins Reared Apart (MISTRA), a multi-decade investigation that, she convincingly argues, influenced a paradigm shift in U.S. psychology.

Choice - J. Mercer

No study of twins has generated as much publicity, media attention, and discussion in the field of behavior genetics as the Minnesota Study of Twins Reared Apart (MISTRA)… All readers will find Born Together—Reared Apart a highly valuable account of the entire project.

Science - Dorret I. Boomsma

In Born Together—Reared Apart, [Segal] has written a meticulous and fascinating account of the study that involved a total of 137 pairs of twins, including 81 identicals raised apart, mainly from the USA and the UK. It wasn’t the first study of its kind, but it was the largest and certainly the most influential.

Tim Spector

Twins separated at birth are endlessly fascinating and give us some of the best scientific insights into nature and nurture. No one can tell this story better than Nancy Segal, gifted scientist, raconteur, and wise observer of human nature.

Steven Pinker

Born Together—Reared Apart is a tour-de-force in the history of psychology and twin research. Describing the twins’ life stories as well as the scientific data, Segal gives us a compelling account of the findings, implications, and controversies from the world famous Minnesota Study of Twins Reared Apart. The book will be essential for anyone seriously interested in the genetic and environmental influences affecting human health and behavior.

Robert Plomin

It is an important book because many of the study’s findings were serious contributions to our bed of knowledge and the book explains why… An important read for anyone seriously interested in genetics or the debate… If you are a professional associated with genetics you will find this book of interest and of value. For those engaged in the Nature–Nurture debate it may be crucial in understanding what traits may be more influenced by nature and which by nurture, and for the layperson it will be of interest for the anecdotes about the twins themselves and how a major study evolved and fared.

Twin Research and Human Genetics - Milton Diamond

This is a vivid and intimate account of one of the classic episodes in the history of the nature–nurture debate by somebody who was part of the team. The Minnesota Study of Twins Reared Apart made a vital difference, against often entrenched conventional wisdom, to the understanding of human development. Nancy Segal tells the story of the project superbly.

Matt Ridley

In this inclusive overview, Nancy Segal…examines the study that turned ideas on parenting, teaching, health and sexual orientation upside down.

Nature

If you harbor any curiosity about why people turn out the way they do, Segal’s topic will fascinate. How big are the effects of nature, nurture and everything else?… A joy to read when she describes the awe of reuniting twins—and the joy of seeing many become soul mates before her eyes.

Wall Street Journal - Bryan Caplan

In this inclusive overview, Nancy Segal…examines the study that turned ideas on parenting, teaching, health and sexual orientation upside down.

Nature Lib

In Born Together—Reared Apart, [Segal] has written a meticulous and fascinating account of the study that involved a total of 137 pairs of twins, including 81 identicals raised apart, mainly from the USA and the UK. It wasn't the first study of its kind, but it was the largest and certainly the most influential.

Lancet - Tim Spector

No study of twins has generated as much publicity, media attention, and discussion in the field of behavior genetics as the Minnesota Study of Twins Reared Apart (MISTRA)… All readers will find Born Together—Reared Apart a highly valuable account of the entire project.
— Dorret I. Boomsma

Science

If you harbor any curiosity about why people turn out the way they do, Segal's topic will fascinate. How big are the effects of nature, nurture and everything else? ...A joy to read when she describes the awe of reuniting twins—and the joy of seeing many become soul mates before her eyes.
— Bryan Caplan

Wall Street Journal

The Minnesota Study of Twins Reared Apart (MISTRA) was initiated in 1979 to help disentangle the effects of environment and genetics on behavior. By studying identical twins reared apart—siblings with 100 percent of their genes in common—any similarities in behavior would be explained by shared genes. Segal (humanities & social sciences, director, Twin Studies Ctr., California State Univ., Fullerton; Someone Else's Twin: The True Story of Babies Switched at Birth) and her fellow MISTRA colleagues examined a range of factors from IQ to sex life, religiosity to psychopathology. The study ended in 1999 after tracking 137 twin pairs. In most of the areas they studied, MISTRA's researchers concluded that genes play an important role in behavior, sometimes even more important than environment. VERDICT With this book, Segal wants to clarify misconceptions about MISTRA, a controversial but popular study that weighted nature as more important than nurture. She responds to criticism by carefully describing MISTRA's tests, methodology, and results. This abundance of hard data will discourage lay readers and, in the end, might not satisfy the critics of the study's original methodology. Recommended for readers interested in behavioral genetics.—Maryse Breton, Bibliothèque et Archives Nationales du Québec, Montreal

Library Journal