Well, to answer that last question- the penis' size is just like the color of one's eyes. Genes account for it, nothing else. However, I am sure that if a father's dick is huge, it does not follow that the son would inherit the size. It may, and then again, it may not.

There is actually a crucial difference. Barring incidents of wearing contacts, there is no way one could change the eye's color. A dick's size could be altered however, using modern medical technologies.

not necessarily