While gorillas are relatively small, chimpos are massively hung indeed!
There have been theories about gorillas being monogamous and chimpos being promiscuous and therefore more competitive in terms of dick size. However, I have not read that extensively in this area of zoology.
As I understand the issue its all about sperm counts. The randy chimps sperm needs to be mutitudinous in order to increase its likelihood of passing its genes onward against formidable competiton. The gorillas - not so much. They are more monogomous. So, You can tell a species monogamy quotient by its testicle size and we are right smack dab in the middle ot the primates.
