[Alex3917]

Not sure if this is true, but I heard recently that the best predictor of IQ is actually the gene that controls determines the size of your mom's vagina, because that is what mediates the risk of brain cell loss due to lack of oxygen at birth. Kind of a funny, but also quite telling about the state of genetics.

[tokenadult]

Not sure if this is true

That's definitely NOT a well replicated finding. In general, no study has ever shown any single-gene allele variation with strong effect on IQ across the general population. There are rare genes (but, really, mostly rare chromosome abnormalities) that have devastating effect on IQ, resulting in mental retardation, but the variance in IQ in the general population above and below the population median is still quite mysterious as to whatever genetic basis it has, as the references I've already shared in this thread will make clear.

After edit: has anyone got a contrary example to the general statement I'm making here? I gather someone disagrees with the statement, but I'm not seeing any citations posted in reply. Feel free to check the citations I've already posted in other replies in this rapidly ramifying thread if you disagree with me and would like to look up facts on the matter.

[goodside]

The two tables here identify specific polymorphic genes and linkage regions predictive of IQ: http://www.psy.ed.ac.uk/people/iand/Deary%20(2009)%20Hum%20G...

[tokenadult]

You didn't speak about the amount and reliability of prediction of IQ in your kind reply. I have referred to that publication. The publication by Deary and Johnson you link to was published in 2009. I was quoting a more recent publication by Wendy Johnson, a frequent co-author with Deary at Edinburgh, in one of my other replies in this thread. Here are a couple of publications by Deary, Johnson, and various co-authors with more recent publication dates than what you have kindly linked:

The review article "The neuroscience of human intelligence differences" by Deary and Johnson and Penke (2010)

http://www.larspenke.eu/pdfs/Deary_Penke_Johnson_2010_-_Neur...

"At this point, it seems unlikely that single genetic loci have major effects on normal-range intelligence. For example, a modestly sized genome-wide study of the general intelligence factor derived from ten separate test scores in the cAnTAB cognitive test battery did not find any important genome-wide single nucleotide polymorphisms or copy number variants, and did not replicate genetic variants that had previously been associated with cognitive ability[note 48]."

Johnson, Penke, and Spinath (2011) "Understanding Heritability: What it is and What it is Not"

http://www.larspenke.eu/pdfs/Johnson_Penke_Spinath_2011_-_He...

"Presuming this is correct and, as Visscher and Keller appear to have implied, applicable to most behavioural traits, this indicates that literally thousands of genes are likely involved in each trait, with no single polymorphism having substantial effect, which is the quasi-infinite model to which Munafo and Flint refer. Whatever would we as psychologists do with such information?"

There are more publications on the issue where these came from. I am familiar with the current literature on the subject, both from an online discussion group hosted by the Behavior Genetics Association and from a weekly "journal club" during the school year (at which I met Wendy Johson, the co-author of the publication you linked to, and of other more recent publications I am linking to in this thread). The hope of many behavior genetics researchers was finding a simple genetic model of normal allele variation in just a few genes having a large and consistent influence on IQ in the normal range. That hope has been dashed by the data as further studies have been conducted, and as researchers attempt to replicate the studies of earlier authors in new data sets.

[goodside]

Conceded and upvoted.

[rada]

Given the prevalence of c-sections and episiotomies, highly unlikely. In 2010, a full third of US babies were not born through the vagina.

[sp332]

That is funny, but babies "breathe" through the umbilical up to several minutes after birth, so I'm sure it has nothing to do with "brain cell loss" or oxygen.

[Alex3917]

That's assuming the birth goes correctly though. If the umbilical cord is wrapped around your neck and you're coming out breech then that's another story. My understanding is that it has a large effect in a small number of cases.

[sp332]

We're talking about "the best predictor of IQ" which is not the same thing as having a large, negative effect in a small number of cases.