What is the average size of the male penis?

In ancient Greek and Roman art, it is common to see smaller male genitalia than one would expect for the size of the man. Renaissance art also followed this aesthetic; note Michelangelo's David (see another comment in the next paragraph). This was due to the belief that an uncircumcised and small penis was desirable in a man, whereas a bigger or circumcised penis was viewed as comical. This may have had to do with the Greeks' adoration of an undeveloped body or the actual size of real models who stood in cold studios. However, it has also been said that artists intentionally depicted the penis size as smaller than usual, to prevent it from detracting from the art form itself. Others have said that perhaps male average penis size back then was significantly smaller, and has become bigger over time much like the average height has. It is also believed that a large penis was believed to be "beastly" or animal. All of these theories are plausible.