Relationship between brain size and intelligence.

Brain size has been decreasing for the past tens of millennia. There is a correlation between brain size and IQ (attempt to measure the recognition of logical patterns). Why is it denied? Any justification for better efficiency must be fully justified (impossible without archaeo-DNA cloning). The current human being is domesticated, in his current environment he does not need as much spatial-empathic intelligence as before, there is no denying that simple fact.