Morgan Worthy explains (in I Have Known the Eyes Already) some independent research done at Pennsylvania State University by people he had never met:
They tested the reactivity hypothesis with human subjects by studying eye color and reaction time in a laboratory setting. They first found that simple reaction time is not related to skin color, but it is related to eye color. They found that dark-eyed blacks and dark-eyed whites have faster reaction times than do light-eyed whites. They then focused just on comparing dark-eyed Caucasians to light-eyed Caucasians on how quickly they could react to a visual or auditory stimulus. They did a number of well-controlled laboratory studies, and then did a meta-analysis of all those studies. Read this quotation which reports the results:
Thus, the findings across studies have consistently shown that dark-eyed subjects have shorter pre-motor time and simple RT latencies than light-eyed subjects. Considering that Worthy’s hypothesis has been experimentally tested seven times with seven different samples … a combined probability value would more accurately reflect the reliability of the eye color phenomenon. Using a z-transformation procedure … a z value was obtained that could not occur by chance any more than one time in 10 million. Worthy’s hypothesis, therefore, reliably predicts RT differences between eye color groups from one study to the next (Hale, et al. 1980, p. 61).
I can live with a probability of one in ten million that my hypothesis is wrong. I wanted you to read that in order to make it clear that the association between dark eyes and quick reactions is very well established in humans.
He concedes that the differences not large in absolute terms:
I had reached the same conclusion by studying performance records of professional and college athletes. Even small differences in the general population can matter when looking at a heavily selected group like professional athletes.
The interesting question in my mind is what has been driving the proliferation of blue eye genes in Northern Europe these last few thousand years. Poor reaction time is probably not it.
Some theories:
1. The hit to reaction time comes with a better sense of timing as per Morgan Worthy. Based on his positions/eye color correlations I would guess this would select to some percentage of the population and then we would have an equilibrium. His correlations generally show the few having blue eyes – leaders, QBs, and so forth.
2. Also from Morgan Worthy, blue eyes are better suited for the lower light conditions of northern foggy areas. Might have something to do with circadian rhythm entrainment, or not.
3. Sexual selection under strict monogamous conditions from Peter Frost. The idea being that females have to stand out from other females in some obvious way. This theory would also lead to mixed equilibriums as the competitive advantage of colorful eyes diminishes when more and more women have them.
There was a huge sex slave trade for most of human history. That’s bound to affect the last few thousand years of evolution.
Where Worthy says ‘hunting’ maybe try ‘sex’? Stalking, Skulking, and Speed/Power.
It all depends on the population that was studied; because simple reaction times correlate with “g” – general intelligence (measured by IQ testing).
If the population studied was, for example, college students from a particular university; then this is essentially selecting a relatively narrow band of IQ – and therefore narrowing the range of reaction times to Much less than the IQ range across the world.
i.e. IQ of student subjects would be high enough to get into that college – so that probably all the subjects in the study had above average IQ for that country.
Also, in most colleges except the most-selective ones, the IQ of subjects tends not to include the highest levels – because these students would usually have chosen to attend more-selective colleges.
Anyway, IF the studies were done on US students at a particular college or a few colleges, this is not representative of the situation across the world.
I say this, because it is well established that simple reaction times (like IQ) have large average differences between races – shortest sRTs in East Asians, longer sRTs in white Europeans, longer again again in Sub-Saharan Bantu Africans and so forth.
Given that races often have different skin (and eye) colours on average, there is almost-certain to be differences in simple Reaction times based on skin colour, IF the sample studied has not been pre-selected (as with college students) to exclude the extremes of slowest (fastest) RT subjects.
Of course I haven’t read the methodology of the studies cited by Morgan Worthy, and it may be that the samples were other than I am assuming!
I just mention this as a very common and very misleading error made in many thousands of published psychology experiments: i.e. by the sampling method used, accidentally controlling away almost all of the variation that is being sought. And ending up measuring something else, a confounder!
Yes, I had many of the same concerns about non-representative samples and range restriction.
(It’s good to see you back, Dr. Charlton. I hope this means you find this a blog worth reading.)