Holmes asked me to open a new thread on this in
A great article about reproductive freedom. I'll respond to his and EZScience's messages here.
I wrote:
The fact that behaviour is roughly 50% genetic (technically 50% hereditary, I suppose) is well known.
EZScience responded:
would have to take issue with your phraseology here.
The fact is, it is the *potential* for particular behavioral traits that has a large genetic component - not their actual expression. That would be genetic determinism and is not accepted in mainstream thinking on the the heritability of behavior.
My initial phrasing was sloppy, I honestly thought this was a well known fact, I shall phrase it more carefully. 50% of the variation in measurable behavioural traits is accounted for by genetic variation (on average, it varies among traits). Here a measurable behavioural trait can be almost anything you can think of a way to measure: e.g. extroversion/introversion, thrill seeking behaviour, addictive behaviour, hours of television watched a day, number of sexual partners or speed while driving.
Note that this isn't a theoretical claim about
how genetics influences behaviour; it's an empirical claim about the observable facts of how genetics and behaviour interact. It's also absurd to claim that this is genetic determinism: it
can't be - in order to be determinism you'd have to 100% genetic influence; that's not the case.
Closer to home, I have to say that I credit a great deal of my own academic accomplishment to the fact I had educated parents who provided me with a highly enriched learning environment from a very early age. My father used to bring home Voltaire, Shakespeare, Sir Arthur Conan Doyle etc. from the time I was in second grade. I consider my wife to be just as intrinsically intelligent as I am, but her intellectual development (and academic accomplishment) lags far behind my own for the simple reason she was severely limited by her environment during childhood and adolescence. Neither of her parents were educated and she had no opportunity for higher education until much later in life. We have often reflected on just what she might have accomplished with more intellectual opportunity earlier in life.
This is a nice story, and I'm glad your parents took such an interest in you. But the evidence suggests that the current vogue for assigning intellectual development to "enriched environments" is simply wrong. It's based both on the notion of a "development window" which has never had any support (excepting specific areas of development such as hearing and vision) and misinterpretation of experiments that show that children tend to be like their parents (a fact far better explained by genetics than any environmental differences).
There are two strong pieces of evidence that point this way: the first is that adoptive children of the same age and sex adopted at the same time are no more similar in intelligence than random strangers. The second is that the correlation between genetics and IQ actually
increases as you grow older not decreases.
On to Holmes:
Sorry to ask you to do some leg work but could you point to any particular study or meta analysis which states this?
I don't have any to hand but I will attempt to locate some for you over the weekend. All of the results I have mentioned so far can be found in
The Blank Slate by Stephen Pinker, which does include an extensive set of references.
But you might be interested by a short read I located:
The three laws of behavioural genetics
To recap lightly: Our brain which controls automated nervous activity, was unquestionably formed by evolution. The apparent evolutionary trend was toward greater autonomous, or noninherently hardwired activity.
This means that brains slowly gained capacities for adaptation to events within a lifetime, rather than instincts passed on and so adapted over generations.
Yes, this is the popular assumption. The trouble is that the evidence strongly suggests it's not true. While humans (and other higher animals) undoubtably do have much greater abilities to learn and adapt to their environments, these abilities are guided by instinct - the way in which we learn is, itself, instinctual and underneath the learning layers we are still strongly instinct driven.
Have a look over
Brown's list of human universals and observe how many seemingly higher behavours have emerged in
every human culture from thumb sucking to rape and incest adversion. Then there's Chomskian universal grammar and the nature of language acquisition. Then there's the genetic causes of homosexual behaviour that I've seen you refer to before. I also refer you once again to the 50% genetics result that has been repeated so often.
If you think about, the notion that human behaviour is entirely learned and does not involve genetics is absurd. Do you really think that you learned to have the same set of emotions as everyone around you? That you learned to be sexually aroused by breasts? That you learned that sexual arousal should cause an erection? That every mother needs to learn to love her child? That every single language on earth uses the same set of categories to divide up the world by chance? It's just not credible.
(Always forget we're supposed to say were it is to go: Is It Science? I imagine)
This message has been edited by Mr Jack, 06-17-2005 06:51 AM
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