Thursday, February 4, 2016

Brain Size, Orbital volume, and National Intelligence

It is well established that populations differ in brain size. The explanation of why is more controversial. This post is going to look at two possible answers to this question.

Some have proposed that populations differ in brain size because some populations have evolved to be smarter than others, and one biological mechanism by which a population can become smarter is to increase its brain size. Others have said that some populations evolved to have larger orbital volumes that others in order to see better, and this increased their over all brain size.

One paper making this argument is Pearce and Dunbar (2011). In this paper, Pearce and Dunbar find a strong correlation between a population's mean orbital volume and the latitude in which that population evolved. The authors theorize that populations distant from the equator evolved large vision related brain areas because of the lower levels of ambient light in such areas. The lead author of the study, when speaking to the press, concluded “we argue that having bigger brains doesn’t mean that high-latitude humans are necessarily smarter. It’s just they need bigger eyes and brains to be able to see well where they live.”

Wolf (2011) wrote a reply in which he took Peace and Dunbar's data set and combined it with national IQ data. He showed that the correlation between total cortical capacity and national IQ is larger than the correlation between orbital volume and cranial capacity. He took this to mean that population differences in orbital volume alone cannot explanation the relationship between national IQ and cranial capacity.

I decided to take this data set and produce a correlation matrix as well as a multiple regression in which orbital volume and cranial capacity are independent variables predicting latitude. I took national IQ data from Lynn and Vanhnnen (2012) and data on the IQ of Native Americans from Lynn (2015). Scandinavia's IQ was calculated by averaging the IQs of Sweden, Denmark, and Norway.

The most surprising finding here is that population IQ correlates more strongly with orbital volume than it does with cortex capacity. However, this may just be due to how well orbital volume correlates with latitude.

Here we see that cranial capacity does continue to predict latitude holding orbital volume constant, but the association has a P value of .14. Given the small sample size of nations being used in this analysis, and the fact that a P value of .14 isn't that far off from conventional significance thresholds, I am inclined to view this as support for the view that brain size is associated with latitude independent of variation in orbital volume.

1 comment:

  1. I would be overjoyed if you could go into greater depth about Asian IQ and the validity of Lynn's data with regard to it, in particular the Northeast variety often said to outpace whites taken as a large whole. Reading discussions on TheRightStuff's disqus board has created a lot of confusion for me lately as to whether Lynn made unsupported inferences about the average IQs of Asian countries in instances where data was actually absent or insufficient from sources he drew from, or ignored sample biases (vis-a-vis self-selected immigrant groups or elite groups of nationals in Asian countries) altogether.
    I would like to stress that I am not at all averse to white ethnic pride (or any other form of ethnic pride, for that matter), but I often find myself having to doubt many of the dismissive and simplistic claims about about Asian intelligence and achievement emanating from the WN side of the fence, as they usually seem tainted by an emotionality and unwarranted sense of personal ego investment that should be beneath the alt-right's dignity.
    I have come to really respect and trust your input on HBD-related subjects the longer I've been reading your blog/watching your videos, so I'm certain you have greater insights than I have been able to glean from my limited reading and comprehension.
    I apologize if I give the appearance of seeming pushy, since I am fully aware that you have a life of your own and can't just write an essay for any person who asks you a question.
    Genuine thanks for your stimulating blog.