Commenter and blogger destructure recently wrote on this blog:

…People from different groups who may have an individual IQ of 70 are not the same because different groups have different averages. The further away from the average one gets, the more likely it is to be the result of a defect. For example, a person with an IQ of 85 from a group that averages 100 is still within 1 stdv. There’s probably nothing functionally wrong with them or at least nothing serious. They’re just not very bright. If you go 2 stdv’s to 70 then it’s no longer an issue of being not bright. The deviation from the norm is so great that there is something wrong with them. However, a person with an IQ of 70 from a group that averages 85 is still only 1 stdv frm average. There’s nothing functionally wrong with them either. They’re similarly not very bright for their group. But you’d have to go lower, perhaps 60 or so, before you started to see the same kind of functional problems you would for someone from a group that averages 100.

To make the point, chimpanzees are often quoted as scoring from 35 to 50 on IQ tests. Yet they’re not defective.

destructure is 100% correct.  A Chimpanzee with an IQ of 40 is far more functional than a human with an IQ of 40 because chimpanzees evolved to function (in their narrow environment) with an IQ that low, and thus evolved other abilities that compensate for a lack of overall intelligence, including certain cognitive abilities as this video illustrates:

I also believe that low IQ human races tend to have certain other compensatory cognitive abilities such as relatively high social IQ, relatively high rhythm IQ or size constancy (the ability to estimate the size of an object at a distance).  Richard Lynn claims that Bushmen and pygmies have the lowest IQs of any human population but cites studies showing they have superior size constancy than whites and says “it implies that the ability may have deteriorated in European and East Asian peoples who gave up hunting about 8,000 years ago and adopted agriculture.”

What this suggests is that low IQ populations may actually be smarter when it comes to adapting to certain situations than high IQ populations , but the real test of intelligence is the cognitive ability to adapt in a wide range of environments and situations.  Brain size tripled in 4 million years of evolution to make room for more and more cognitive abilities, and increasingly general cognitive abilities (i.e. abstract reasoning) until humans had a large and flexible enough behavioral repertoire to adapt in almost any environment on Earth, and perhaps some beyond.