Nature VS Nurture and Twin Studies


First, sorry for the first post, it’s gone. I’ve just learned something about ‘Link’ posts.


This isn’t the most comprehensive article about all the separated twin studies that have been done, but it’s new, and typical enough. Here’s an excerpt, a link to the article and the author’s data, then my comments:


“To explain this close bond, psychologists frequently look to environmental factors: Identical twins, growing up in lock step, share most of the same experiences (they are often even treated the same by others) and therefore develop their unusually strong connection. But my research on reunited twins challenges this theory. I have found, for example, that reunited identical twins report feeling greater closeness to each other than do reunited fraternal twins. And I have found that a reunited twin generally reports feeling closer to the twin he only recently met than to a genetically unrelated sibling with whom he was raised.

Given that reunited twins were not reared in the same environment, genetic factors are surely relevant to these bonds. But how do shared genes result in an immediate sense of connection?”


Nancy L. Segal, a professor of developmental psychology at California State University, Fullerton, is the author of “Born Together — Reared Apart: The Landmark Minnesota Twin Study.”


How different are the environments really? Don’t we all raise our kids the same way, with the same methods? And even in the case of these ladies, isn’t American culture and therefore American child-rearing simply a continiuation of the British version? Aren’t the apparent differences from household to household superficial? For this, I offer the relative ubiquity of parenting books and discussions where the basic premises are nearly universal while only the details of how and when parental control is exercised differ.

Which makes me wonder that we are not looking at the correlation of genes in interaction with different environments, but genes in correlation to environments that are actually also very similar. Again, within a given culture, how different are the environments provided for children? This idea would have to extend to the sorts of personality tests that the twins do so similarly at: are the described personality traits and types not also visible only in contrast with a fairly uniform background? If so, the power of our genes, and so of the Nature over Nurture argument, is going to win every time, considering that there really be very little variation in the environment children are raised in anyway.