Born Together―Reared Apart: The Landmark Minnesota Twin Study

by Nancy L. Segal

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.

Genres: Psychology, Science, Nonfiction, Genetics, Anthropology

416 pages, Hardcover

First published June 18, 2012

About the author

I am a Psychology Professor at California State University, Fullerton, with a special interest in twin studies--I am a fraternal twin myself! I have always been fascinated with the differences between my sister and myself, as well as the similarities and differences between identical twins. My career has been informative, and so much fun! And I am very excited about my recent books.

When I am not being an academic you can find me swing dancing or watching old films.

Reviews

[Christopher Litsinger · Rating 1 out of 5]

This tried to be 3 books at once.
It is one part pleasant stories about the twins that were studied. This was probably the most interesting part, but it was also the sparsest.
Next was a sort of personal reminiscence about being a scientist on the MISTRA study. This was less interesting and frequently got quite defensive (about things like funding, or critical articles written about the study).
Finally we had study results in more or less scientific journal form. Here you get fun stuff like:

The information processing data were organized into three components: overall speed of response (29.8 percent), speed of information processing (20.8 percent), and speed of spatial processing (16.7 percent); the percentages reflect the proportion of variation in information processing explained by these components. Overall speed of response correlated significantly with the general cognitive ability measures (r = -0.31), verbal reasoning (r = -0.18), and perceptual speed and accuracy (r = -0.20). The negative correlations mean that faster responding was associated with higher test scores. Speed was associated with both general and specific mental abilities, supporting the view that processing speed is a major part of intelligence. Speed of information (memory) processing correlated significantly with general cognitive ability (r = -0.32) and with verbal reasoning (r = -0.27). Speed of spatial processing correlated mostly with spatial processing measures (r = -0.32).

Any one of these parts by themselves probably would have made a nicely readable book (although the last one would have probably taken me a long time to read). All of the mixed up together following more or less chronological order was just a mess.
Very disappointing; I'll need to go back to searching for a good book about twins.

[Dawn · Rating 5 out of 5]

Highly impressed with this huge reared apart-raised together twin studies as I am really interested in twins. This study involving identical and fraternal twins made many discoveries of what we now know are inherited traits. While I am sure that there are many new, current twin studies that can use brain imaging and DNA studies, this was a huge study for the times that ran close to 30 years involving many professionals and grad students.

So interesting the meetings between identical twins that may not even have known they had a twin. So amazing the similarities between the twins that are inherited since they were not raised together. I found the entire book both fascinating and challenging to read.

[Michelle]

"Full siblings (and DZ twins) have a 50 percent chance, on average, of sharing the same gene at a given locus. Some siblings (and DZ twins) will share over 50 percent of the same genes, and some will share less." 56
See!! It is possible (though statistically extremely unlikely) to be totally genetically different from your sibling. (at least in terms of inheriting these genes from the same place)

"Heritability is the proportion of population differences in intelligence, height, or running speed that is associated with genetic differences among the members of a population. To say that running speed has a 33 percent heritability in ten-year-old females means that about one-third of the population differences in that trait are explained by the genetic differences among the young female members. It does not mean that one-third of a particular young girl's running speed is associated with her genes." (61)

Stopped on page 70

[Susan · Rating 4 out of 5]

I've always been interested in nature vs. nurture. It was interesting to learn that separated twins can turn out to be extraordinarily alike in their adult lives, even if there younger years were substantially different. Very scientific with a lot of data, but still very interesting and readable.

[Mills College Library]

306.875 S4543 2012