A while back I had estimated that H. Erectus had an average IQ of 55 based on the fact that they had the tool making ability of a 1979 Western seven-year-old, but more recently I had down graded them to an IQ of 40, based on my assumption that they had the symbolic IQ of 40.
My logic was that their tool making ability only represented their spatial IQ, but a symbolic IQ of 40 dragged down their COMPOSITE IQ to 40.
Brief comment on composite IQs
Statistically naïve readers might be wondering why a spatial IQ of 55 and a symbolic IQ of 40 equals a composite IQ of 40, and not a composite IQ of 48 (the average of 55 and 40). The answer is that IQ is just a measure of where you rank compared to neurologically normal Northwest Europeans and ranks CAN NOT be averaged to give composite rank, unless the two sub-rankings correlate perfectly. So if you rank super low in BOTH cognitive domains, then your rank order in the COMPOSITE of both domains will be LOWER than the average of the two, because impairment at BOTH domains is so rare that it pushes your composite way down in the pecking order. The opposite is true for people who excel in BOTH domains; their composite IQs are HIGHER than the average of each subscale.
Why the apology?
So why am I apologizing to H. erectus? Because I was wrong to assume their symbolic IQ was only 40. That assumption was based on the fact that they couldn’t draw AT ALL, thus suggesting they had extremely impaired understanding of symbols or representations. People who can’t draw ANYTHING obtain an IQ of only 19 on the Draw-a-man test (corrected for old norms), however correcting for culture bias (H. erectus lived in the wild), I raised it to about IQ 40.
How did I know they couldn’t draw? Because as far as we know, they never drew a single thing in the nearly 1.9 million years they walked the Earth. However a friend suggested that perhaps they could draw, they just never had the IDEA of drawing. Inventing the idea of drawing is much more difficult than drawing, so if they never had the idea in the first place, I can’t assume they were too dumb to execute the idea.
Thus there’s no evidence that H. erectus had a symbolic IQ as low as 40, and the only hard evidence of their IQ remains their tool making ability which equates to an IQ of 55. Since this is the only data point, I have no choice but to tentatively accept it as their IQ. And frankly it makes a lot more sense than IQ 40, which is getting into chimpanzee territory.
How much IQ is needed to have the IDEA of drawing?
So while it takes an IQ of only 40 TO draw, how much IQ is needed to come up with IDEA of drawing, if it never existed in your world before? If you believe in the controversial field of HBD, then perhaps the lowest IQ people in the World are the Bushmen with a genetic IQ of perhaps 72. Yet even they appear to have come up with the idea of drawing as evidenced by their ancient rock art, so unless a more advanced people taught them this skill, then a population with a mean IQ of 72 is capable of inventing drawing.
What about Neanderthals?
So what about Neanderthals who also never drew? Earlier I wrongly suggested this implied they too had a symbolic IQ of only 40 (commenter Melo to his credit strongly disagreed) and yet I also speculated that they must have had a much higher spatial IQ to have survived in Northern Europe. Overall I pegged their mean IQ to be 62.
I still roughly agree with this estimate, but my logic was wrong. Better logic is as follows: They were more technologically advanced, more evolved, and bigger brained than H. erectus, so they probably an overall IQ above 55 (H. erectus level); yet they apparently never had the IDEA of drawing, so they were probably lower than Bushmen (perhaps genetic IQ 72 if you take HBD seriously). Thus, splitting the difference gives an IQ of 64.