Twin Studies

The Trouble with Twin Studies questions popular genetic explanations of human behavioral differences based upon the existing body of twin research. Psychologist Jay Joseph outlines the fallacies of twin studies in the context of the ongoing decades-long failure to discover genes for human behavioral differences, including IQ, personality, and the major psychiatric disorders. This volume critically examines twin research, with a special emphasis on reared-apart twin studies, and incorporates new and updated perspectives, analyses, arguments, and evidence.

Twin Research: Biology, Health, Epigenetics, and Psychology is a comprehensive, applied resource in twinning and twin studies that is grounded in the most impactful findings from twin research in recent years. While targeted to undergraduate and graduate students, this compendium will prove a valuable resource for scholars already familiar with twin studies, as well as those coming to the field for the first time. Here, more than forty experts across an array of disciplines examine twinning and twin research methodologies from the perspectives of biology, medicine, genetic and epigenetic influences, and neuroscience. Chapters provide clear instruction in both basic and advanced research methods, family and parenting aspects of twinning, twin studies as applied across various disease areas and medical specialties, genetic and epigenetic determinants of differentiation, and academic, neurological and cognitive development. The presentation of existing studies and methods instruction empowers students and researchers to apply twin-based research and advance new studies across a range of biomedical and behavioral fields, highlighting current research trends and future directions. Offers unique insights into twinning rates, mechanisms and factors surrounding twinship Provides clear instruction on both basic and advanced twin research methods and study design Features leading international experts in twin biology, genetics, health and psychology Examines findings from recent twin studies across a broad array of health and behavioral studies

Few would dispute the truth of the statement `People are Different', but there is much controversy over why. This book authoritatively explains the methods used to understand human variation, and extends them far beyond the primary `nature or nurture' question. After chapters on basic statistics, biometrical genetics, matrix algebra and path analysis, there is a state-of-the-art account of how to fit genetic models using the LISREL package. The authors explain not only the assumptions of the twin method, but how to test them. The elementary model is expanded to cover sex limitation, sibling interaction, multivariate and longitudinal data, observer ratings, and twin-family studies. Throughout, the methods are illustrated by applications to diverse areas such as obesity, major depression, alcohol comsumption, delinquency, allergies, and common fears.

This volume is about an ongoing long-term research initiative led by researchers from the School of Dentistry at the University of Adelaide. The aim of this book is to provide an overview of the studies of the teeth and faces of Australian twins and their families that have extended over more than thirty years.

The Minnesota Study of Twins Reared Apart startled scientists by demonstrating that twins reared apart are as alike, across a number of personality traits and other measures, as those raised together, suggesting that genetic influence is pervasive. Segal offers an overview of the study’s scientific contributions and effect on public consciousness.

A 2022 Choice Reviews Outstanding Academic Title Takes the first in-depth look at the New York City adoption agency that separated twins and triplets in the 1960s, and the controversial and disturbing study that tracked the children’s development while never telling their adoptive parents that they were raising a “singleton twin.” In the early 1960s, the head of a prominent New York City Child Development Center and a psychiatrist from Columbia University launched a study designed to track the development of twins and triplets given up for adoption and raised by different families. The controversial and disturbing catch? None of the adoptive parents had been told that they were raising a twin—the study’s investigators insisted that the separation be kept secret. Here, Nancy Segal reveals the inside stories of the agency that separated the twins, and the collaborating psychiatrists who, along with their cadre of colleagues, observed the twins until they turned twelve. This study, far outside the mainstream of scientific twin research, was not widely known to scholars or the general public until it caught the attention of documentary filmmakers whose recent films, Three Identical Strangers and The Twinning Reaction,left viewers shocked, angered, saddened and wanting to know more. Interviews with colleagues, friends and family members of the agency’s psychiatric consultant and the study’s principal investigator, as well as a former agency administrator, research assistants, journalists, ethicists, attorneys, and—most importantly--the twins and their families who were unwitting participants in this controversial study, are riveting. Through records, letters and other documents, Segal further discloses the investigators’ attempts to engage other agencies in separating twins, their efforts to avoid media exposure, their worries over informed consent issues in the 1970s and the steps taken toward avoiding lawsuits while hoping to enjoy the fruits of publication. Segal's spellbinding stories of the twins’ separation, loss and reunion offers readers the behind-the-scenes details that, until now, have been lost to the archives of history.

Research today demands the application of sophisticated and powerful research tools. Fulfilling this need, The Oxford Handbook of Quantitative Methods is the complete tool box to deliver the most valid and generalizable answers to todays complex research questions. It is a one-stop source for learning and reviewing current best-practices in quantitative methods as practiced in the social, behavioral, and educational sciences. Comprising two volumes, this handbook covers a wealth of topics related to quantitative research methods. It begins with essential philosophical and ethical issues related to science and quantitative research. It then addresses core measurement topics before delving into the design of studies. Principal issues related to modern estimation and mathematical modeling are also detailed. Topics in the handbook then segway into the realm of statistical inference and modeling with chapters dedicated to classical approaches as well as modern latent variable approaches. Numerous chapters associated with longitudinal data and more specialized techniques round out this broad selection of topics. Comprehensive, authoritative, and user-friendly, this two-volume set will be an indispensable resource for serious researchers across the social, behavioral, and educational sciences.

The Trouble with Twin Studies questions popular genetic explanations of human behavioral differences based upon the existing body of twin research. Psychologist Jay Joseph outlines the fallacies of twin studies in the context of the ongoing decades-long failure to discover genes for human behavioral differences, including IQ, personality, and the major psychiatric disorders. This volume critically examines twin research, with a special emphasis on reared-apart twin studies, and incorporates new and updated perspectives, analyses, arguments, and evidence.

A leading expert on twins delves into the stories behind her research to reveal the profound joys and real-life traumas of 12 remarkable sets of twins, triplets, and quadruplets. Segal unravels these moving stories with an eye for the challenges that life as a twin (or triplet or quadruplet) can pose to parents, friends, and spouses, as well as the twins themselves.

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.