There are correlations between having a dick and being rational. Maybe this next part hasn't been proven, maybe it's being proven, but a positive correlation for Testosterone is likely.
What we do know is that testosterone levels decline with age, which correlates with stupid, grumpy, and stubborn old grandpa. Testosterone calms you down which is important for clear thought; we've proven it reduces anxiety by injecting male and female mice with two doses of it: HTTPS://www.ncbi.nlm.nih.gov/pmc/articles/PMC4330791/
Science is wonderful, but there are still many unanswered questions in dick science. What genes affect dick length and pleasure, and can we know how to genetically engineer a change in vitro? Can we know why are masculine women and transsexuals so angry, and why do they want to destroy all dicks? Did testerosterone deficiency cause Sam Harris to decide to go to India to get a sex change? Because there is no reliable way to prove Sam Harris has a dick over the Web, I consider myself agnostic, as with the other questions.