I should be sleeping because I have a long day at work tomorrow and a huge weekend of drunken partying, but I am so excited about this post that I must write it right now.
I’ve posted about the IQ of Homo Erectus before, but in this post, I will refine my analysis in light of better understanding.
Technological IQ 55
Experiments suggest that it’s not until a child is seven that she has the mental capacity to create the kind of stone tools Homo erectus created. In other words, Homo erectus may have had the intelligence of a Western seven-year-old. On the WISC-R IQ test, an incipient adult (age 16.9) who performs like a seven-year-old on the spatial construction subtest scores lower than 99.5% of biologically normal members of his generation. In other words, an IQ of about 60.
But we should keep in mind that the research on seven-year-old tool making ability was published in 1979. Probably because of better nutrition/health,truly culture reduced spatial skill has been improved by about 0.2 points a year until 2006 (when U.S. nutrition gains seem to have ended). So Homo erectus probably had an IQ around 55 on the most recent culture reduced Western norms (U.S. white norms).
Draw a man IQ 6
In 1.9 million years, H erectus was too stupid to draw anything, let alone a man, so on the on the Draw a Man IQ test he would have scored a bit fat goose egg: zero.
What IQ does zero equate to?
On the Goodenough-Harris Draw-A-Man test, the mean and standard deviation for U.S. 15-year-olds (considered adult level for the purpose of this test) is 46.3 and 9.1 respectively, so zero equates to an IQ of 24 (U.S. norms) or 19 (U.S. white norms). But because these norms were published in 1963, and norms on this test became inflated at a rate of 3 IQ points per decade (Lynn, 2006) until at least 2006, we must reduce this IQ to 6 on modern white norms.
Correcting for culture bias, Draw-A-Man test suggests an IQ of 26
Because even the Draw-a-man test is culturally biased, we must do our best to adjust for the stone age environment H erectus lived in. It’s well known that on typical IQ tests, dropping out of school causes IQ scores (though perhaps not real intelligence) to drop by 2 points per missed year, and research on adopted kids shows that each extra year of education in the rearing parent raises a child’s IQ score by 1.17 points. Although such cultural biases fade by adulthood, as scholars Dickens and Flynn brilliantly noted, this is only true within generations. Between generations these environmental effects are permanent.
So considering the average H erectus had about 13 years less schooling than today’s average white, this would artificially depress his IQ by 26 points. Further, being raised by parents with 12 less years schooling than today’s average white would artificially depress his IQ by another 14 points. So these two cultural biases together should artificially depress his IQ by 40 points on a typical IQ test, but because the Draw-A-Man test is only about half as culturally biased as a typical IQ test, we’ll say it’s depressed by only 20 points.
You might ask, why, if the Draw-A-Man test is only half as culturally biased as a typical IQ test, does it show the full 3 point a decade Flynn effect. The answer is because the Flynn effect is not entirely cultural, it’s also biological (nutrition) and Performance IQ tests like Draw-a-man are sensitive to nutrition (which H. erectus had plenty of).
So adding 20 IQ points to their IQ of 6, to compensate for the test’s cultural bias, raises them to IQ 26.
I realize such corrections are very simplistic, but it seems to give believable results.
Assuming a technological IQ of 55 and an artistic IQ of 26, and assuming only a 0.35 correlation between the two, Homo erectus had an overall IQ of 29!
Brain size of Homo erectus
According to Wikipedia:
H. erectus fossils show a cranial capacity greater than that of Homo habilis (although the Dmanisi specimens have distinctively small crania): the earliest fossils show a cranial capacity of 850 cm³, while later Javan specimens measure up to 1100 cm³, overlapping that of H. sapiens
The below chart shows a line of best fit for the average genetic brain size and the average genetic IQ for contemporary human races (based on controversial estimates many would consider pseudoscience).
If we extend the trend line to extinct Homo species like Erectus, and if we assume Erectus reached their genetic potential for brain size and IQ (early hunter/gatherers living their natural life style seemed to have far better nutrition than all but the most recent First World agriculturalists and Erectus eventually learned to cook its food, digesting even more nutrients) then we can estimate from their brain size that they had an IQ of about 5 when they first appeared, and 40 by the time they went extinct. Averaging the two estimates, gives an IQ of about 23, not that different from the 29 we got based on a historiometric analysis of their technological and artistic talent.