I have looked at the correlations between penis size and IQ. The data for penis size are for erect length and circumference. And volume calculated from length and circumference.
My sources are:
The correlation between penis length and IQ is -0.28. The higher the IQ the lower the penis length.
It is very interesting that the correlation between penis circumference and IQ is only -0.05, which is not significant. I would say that there is no correlation between penis circumference and IQ, but the real negative correlation (weak to medium) is due to penis length.
Correlation change with IQ is quite stable, different than homicide rates and alcohol comsumption case. And the value of correlation is most of the time around -0.35 rather than the total correlation of -0.28.
When we look at the circumference plot, we see the data everywhere.
There is an interesting behaviour one can observe here. Although the correlation is quite weak, we see some normal distribution. Around IQ 90, the circumference is lowest, and gets higher the further IQ from the mean of 90. Maybe this is due to the many number of countries around mean, however we see only change in the lower side than the higher side.
We can also look the correlation change with increasing IQ mean.
The correlation for circumference is quite stable actually,with very weak correlation.
It might be interesting to know IQ correlation within a society, rather than accross countries. We might see a different picture then.