Separate Lives: Why Siblings Are So Different by Judy Dunn and Robert Plomin, Basic Books, 1990, $19.95

Reviewed by John A. Speyrer

Oftentimes parents insist that in spite of treating their children the same they have turned out to be quite different. Does this prove the overbearing influence of genetics on personality? The authors of Separate Lives make a convincing argument that the answer to that question is that it does not. As one's first child develops, it `s easy to point out the effects of environment. But since subsequent children are so different from the first born and from each other, the proponents of nurture become converts to genetic determinism. Identical twin studies have shown the importance of heredity, but the authors claim that it also shows the importance of environment since even though those twins have 100% genetic similarity, they are only about 50% similar in personality. This source of dissimilarity, they believe, can only have one origin and that has to be the environment.

But are not these siblings brought up in the same environment? The authors' thesis is that the environment only seems the same. To each sibling the perception is different which explains why they turn out so remarkably different. The book is based on many studies of differences in characteristics of siblings as well as accounts of famous authors of their perceptions of their own early childhood. An interesting background in Mendelian genetics is given as well as the results of genetic research since Mendel. All of this serves as a background to support the author's contention that environmental factors are the origin of differences in siblings.

Dunn and Plomin contend that what runs in families is DNA and not shared experiences. Viewing the problem from many different angles, the authors continuously reassert throughout the book that a shared environment should make siblings the same but in fact they are not the same. Similarities between siblings can be completely explained by heredity, but what about their differences? The environment can be the only possible source they say. Furthermore, the correlation in similarity of adopted siblings is nearly zero. This means that environmental factors which are non-shared account for all of the differences between such siblings.

When I arrived at chapter 4, entitled ``The Impact of Parents,'' I thought, ``This is it!'' But I was disappointed in its contents. Beginning with comments from famous sibling authors, the duo conclude that mothers are quite consistent in their treatment of their children of the same age. This, suggests, according to our two authors that, children are influenced by how they perceive their parents relating to their siblings, so it becomes important to look at the child as a member of a family unit and not the directly relationship between the parent and the child. In other words, it is claimed that it is the perceived differences in treatment which makes the difference, not the treatment itself. This conclusion is repeated ad nauseam by the authors. They claim that this holds true for ``normal'' family units and not those where child abuse is present. It is almost as though they believe that child abuse cannot happen in a ``normal'' family.

The rest of the book deals with sibling influences, and outside the family influences such as school, peers, later childhood development and the importance of chance factors in development. The authors of Separate Lives conclude by saying that their study sends a ``strong message about the importance of non-genetic factors on development.'' This is in spite of the current fad in biological determinism which is so prevalent in the study of psychopathology today. It is felt that by understanding how the environment affects children, we can properly restore a balance between research of heredity and environment.

Hey, Judy and Robert, primal theory has a lot of correct answers to some of the problems and questions you posed! When will researchers wake up to the truths uncovered during over two decades of experiences by deep feeling regression therapists and their patients throughout the world?

But in spite of my frustration, it's reassuring to have such a study support the premise of the importance of one's childhood environment in determining personality. Even though it is incomplete, this book goes a long way in emphasizing the important of nurture in personality determination. However, we in primal therapy know that the influences of one's upbringing goes back much further in time than even the authors suspect.

Note: An important omission from this discussion was the effects of birth trauma. Pre- and perinatal traumas can set biological and neurological "templates" which will be with a person for life. It can also make an infant and child more needy and thereby exacerbate the results of slight hurts which would not be detrimental to an infant born without such earlier experiences in his background.