Identical Twins Separated at Birth

The psycho world is fully informed, but has not quite incorporated the research. It appears to answer the old question of what counts more: nature or nurture? How much of human development is written into a child's DNA and how much of it is influenced or produced by parental intervention.

How can you study such an issue? Easy. You need to examine the cases of identical twins separated at birth. That is, identical twins who were put up for adoption and raised by different parents in different places… and who have not met each other.

The first case study involved two men, named Jim Springer and Jim Lewis. You will see that their similarities go well beyond appearance and personality. Some of the coincidences are downright uncanny.

The case dates to several decades ago. Henrik Dyneson reports:

Springer and Lewis were identical twins, separated just four weeks after they were born. They had grown up in separate families, 40 kilometers apart, and only met one another for the first time at the age of 39. Astonishingly, they shared many uncanny similarities: both had married women named Linda, followed by women named Betty; both had named their son James Allen; both were diligent amateur carpenters; both were heavy smokers; their favorite beer was Miller Light; both bit theirs nails; both encountered heart problems in their 30s; and both had suffered from migraine attacks at the same age.

Dyneson continues:

The Jim twins provided an almost perfect control experiment; they were genetically identical but raised in separate environments, so any differences between the two men could be attributed to environmental influence and separated from the influence of their shared genetic inheritance.

Researcher Thomas Bouchard explained that these studies threaten much received psychological wisdom. After all, psycho professionals have persuaded parents that they are responsible for whatever happens to their children. And they have persuaded said parents that they must follow the counsel of developmental psychologists, the better to avoid ruining their children. If the twin studies point away from nurture and toward nature, many of said psycho professionals will see their theories go up in smoke. They will also see their influence diminished significantly. And their businesses will become far less viable.

In Bouchard’s words:

This kind of finding, though, it seems to me, threatens a great deal of psychological theory. There is a lot of theorizing in psychology about the tremendous importance of the family situation, the peculiar things that happen when you are growing up. And we turn around and we look at these twins that have been reared in entirely different families and they are just as similar as twins reared in the same family!

And, of course, these studies relieve parents of responsibility for everything that happens to their children:

Twin studies have uncovered the enormous importance of genetics. They have laid to rest the notion that parents are omnipotent sculptors, and a child is a piece of clay. They have hammered another nail into the coffin of the Freudian guilt complex, where everything that goes wrong in an individual’s life may be attributable to poor parenting.

This is not to say that the twins grow up to be identical in all ways. Yet, the researchers suggest that if family matters less than we think, then perhaps social and cultural environment matter more than we imagine. Consider researcher Judith Harris’s argument about the importance of peer influence:

… the effect of being raised in the same family is smaller than the effect of genes. Judith Harris called attention to this theory in her 1998 book The Nurture Assumption, and was subsequently defended by Harvard psychologist Steven Pinker in The Blank Slate. Pinker encouraged parents to stop fretting about what they had or had not done in order to turn their offspring into wonderful individuals. Parents, he argued, do not hold their children’s future in their hands, only their present. Pinker emphasized that parenthood remains an awesome ethical responsibility, and that it is important to give one’s child a childhood worth remembering. But parents cannot shape a child’s personalities and IQ as a sculptor fashions clay. As Dr. Nancy Segal has put it, homes do matter, but they do not make people alike.

In other words, while about 50 percent of the variation is due to the environment, this environmental effect does not come from the family. Instead, it may be produced by the wider culture, society, the neighborhood, school, peer-groups and friends, but also simply chance: random encounters or openings in the social hierarchy, cosmic rays that damage a piece of DNA, neurons that go zig instead of zag, and so on.

Of course, the twin studies assume that the children were brought up in environments that were roughly similar. We do not, to my knowledge, have studies about twins brought up in widely divergent environments, receiving completely different levels of care and/or neglect.

Within the field of psychology these twin studies have now been widely accepted. If they cure us of the notion that human beings are born as blank slates, or as lumps of clay, to be fashioned entirely by parental influence they will be providing a great service.