Personality & Intelligence: The 50-50 Rule

[Pythagorean]

In these lectures on Human Behavioral Biology (which I've posted here:)

https://www.physicsforums.com/showthread.php?t=475074

the "behavioral genetics" portion of the lectures goes into the details of how they measure "% contribution" and talks about the criticisms with it (and there are many)

They basically set up a 2x2 grid. In each grid, they choose a trait that an adopted person exhibits, then they compare to adopted and biological parents.

So basically, if the subject has schizophrenia, there's a x% chance their biological parent (the yes-no square of the grid) has it, a y% chance their adopted parent does (the no-yes square of the grid, and z% chance (where z can be greater than x+y) both your adopted and biological parent had it (implying a synergistic effect) (yes-yes). And of course, some (no-no) chance.

Criticism: now you have all the environmental effects of adoption (and the intentional effects; adoption clinics try to match kids with parents)

But also you haven't subtracted the environmental effects in the womb.

The above research method is now conducted with twin separated at birth, for a better genetic "control" but there still can be problems with considering the environmental effects even in the womb, especially if the twins don't share a placenta.

 

[DanP]

Unfortunately this is the old "nature versus nurture" argument made by racists and eugenicists that argue that IQ is primarily genetic in order to push their agendas to wipe out races and people of "lower IQ" that are incapable of producing intelligent offspring, in their opinion.

Neried and I fought this battle for at least 2 years here against those that were pushing this train of thought. We won.

How exactly did you won ?

In the first place there is not nature vs nurture. You simply cannot talk the effect of a gene in general, in any environment. What you can say is: expression of gene X in environment Y leads to blah blah blah. Expression of gene X in environment Z leads to bal bla bleh

The right way is to talk about how different factors modulate behaviors. You say that 50-0-50 is a nature vs nurture. False. How can be nature vs nurture when in this theory 50% is attributed to social influences (peers) ?

It is somehow disturbing that anyone which talks about genes in the context of behaviors is labeled a nazi, an anti-woman, an instigator to genocide.

Humans seems to harbor some irrational fears about discovering the truth behind human nature. There is a blind will to see humans as either blank slates on which our golden society can write anything , either as innately and fundamentally good or moral creatures. Wrong. We are apes. With a highly sophisticated social structure , but nevertheless, just apes. With genes whose expression can make us strong and fearless, or as anxious and fearful as a rabbit in front of a fox.

I wouldn't go as far to say that parental influences worth 0. But they are also way less important then credited for IMO. I think the best way for a parent to shape the development of a child is to fork enough money to put him in very good schools and universities. Places where he is forced to find his way in a hierarchy of what are usually highly educated, highly competitive individuals. Money for a Ivy league education will make your kid successful. Or at least, help making strides in that direction.

 

[DanP]

That much does seem clear--whether the kid has a preference for a certain color or type of music or scores 112 on an IQ test seem far less important than how successfully the kid navigates the world and applies/reigns in certain hardwired predilictions is more on point in understanding ourselves and how best to maximize human potential.

And where do you think someone is most likely to learn to navigate the social world ? In the confines of a home and from interaction with his mother, or from immersion in the environment and continuous effort to adapt and navigate (that would be his peers).

And a point which must never be forgotten, is that navigating the social world is ultimately done by a biological formation, mainly the PFC. While PFC matures very late in the life of an individual, around the age of 25, suggesting that is the least constrained genetically part of the human brain, but that doesn't mean that it is free from genetic constraints. Navigation of social world doesn't happen by magic, it is biologically mediated. What if your neurobiology of PFC is heritable ? Less receptors for a certain neurotransmitter. Less activation in the pathways which allow PFC to control the dopaminergic receptors in mid-brain What then ? Doesn't the modulation on social behavior , modulation which may be traced in expression of ceratin genes, become as powerful as the predisposition toward a certain color or the 112 IQ ? It is not something that can be neglected.