"Much of the critical evidence has emerged through the study of twins. Identical twins share all their DNA, while fraternal twins share only half - they are no more closely related on a genetic level than are ordinary siblings. Both kinds of twins, however, share a womb, a family and a cultural environment. Comparisons between the two types can thus tease out the extent to which inheritance is important."
Except that different kids have different experiences growing up. The same family does not mean exactly the same life. It's just not true that genes are the only difference between fraternal twins.
This can all be better explained by interactions between culture and genes, than by just genes. But the studies tend to ignore those, because they're too hard to deal with.
(If anyone knows a twin study which does adequately deal with gene/culture interactions, please post it.)
Identical twins reared apart are much more similar than fraternal twins reared together.
And to me at least it makes a lot of sense. If you share almost 100% of your DNA with someone else, I'd expect you to look the same on the outside - that's a given. In the same way I'd expect your brain to be highly similar and therefore it makes sense that you will behave similarly in a lot of situations even though you were reared in completely different environments. I mean you're not gonna get a different color hair just because of environmental differences, so applying this to brain development is not such a stretch.
But why do you think the structure of one's brain affects personality?
We have these things called universal computers. Differently structured CPUs run the same programs. It doesn't matter so much which CPU you have, they all have the same capabilities.
Why should it be different with brains? I think brains are universal knowledge creation devices, and universal means universal, structural changes won't alter the feature set.
The brain is not a general purpose computer running the "me" program. The brain _is_ the "me" program - the software is in the structure of the hardware. Different software yields different results. IANAN(...euroscientist) though, I just like reading Oliver Sacks et al., so take that opinion with a pinch of salt.
There's lots of research that shows that the structure of the brain IS very important in how it works and how we use it. For a good overview see Steven Pinker's How the Mind Works.
Many of these studies include individuals that had isolated damage to one small part of the brain and how that affects them. They show that specific parts of the brain are involved in highly specialized activities and that the brain is not just a big, nebulous general purpose calculator.
"The concordance between identical twins, however, is rarely 100 percent - their IQ scores, for example, tend to be around 70 percent similar, compared with around 50per cent for non-identical pairs. By definition, inheritance therefore cannot be the only factor involved: if it were, identical twins would always turn out the same."
Surely "percent" is the wrong term here, which is puzzling, because why wouldn't the author of the submitted article, who is also the author of the book the article is based on, use the correct term?
Take a regression correlation, multiply by 100, and you have a crude sort of "percent". People intuit percent better than more complex (yet probably more mathematically rigorous) comparisons. If the book is written for a lay audience, this seems like an appropriate term.
That probably is where his "percent" is coming from, but I'm so used to reading even popular literature that doesn't dumb things down like that (preferring to explain typical ranges of correlations) that it was jarring to read that in the newspaper article. Maybe the newspaper editors imposed that on an author who does better in his book.
But what exactly does it MEAN to say "their IQ scores, for example, tend to be around 70 percent similar" when IQ scores have their own scale?
What I find more interesting than nature and nurture here is the censorship of scientific research.
Many of us would like to base our cultural views, morals and laws on the findings of scientific research. It seems more reasonable than the flying spaghetti monster. But are we really prepared to change our views where the science doesn't match up?
On the other hand, I don't think anyone expects science to always be "squeaky clean", free of all political influence.
>Nature works through nurture, and nurture through nature, to shape our personalities, aptitudes, health and behaviour. The question should not be which is the dominant influence, but how they fit together.
Of course, when discussing "nature" in this context, it is always between two humans. Why, how's the nature/nurture debate between humans and skunk cabbage going? Of course, nature is highly determinant there. When you compare a very stupid human, and a very intelligent human, you are in an absolute sense comparing two extraordinary creatures whose extraordinariness is wholly genetic. Their itty-bitty differences (auto mechanic vs. auto engineer) are how we measure ourselves in a power-spectrum and skew our perceptions.
It doesn't matter: Private sector eugenics is already emerging and will settle all bets.
Except that different kids have different experiences growing up. The same family does not mean exactly the same life. It's just not true that genes are the only difference between fraternal twins.