It's also interesting to note that evolutionarily, asians tend to be the the most growers and then caucasians, and then blacks are the most showers.
It had to do with the environment when our ancestors spent time separated for tens of thousands of years. Asians were in a colder climate with constant sun which led to thick black hair, extra fat in the eyelids to protect from the cold, and the penis would retract when unused for the same reason.
Caucasians were in a fairly cold climate as well but with many forests that led to less direct ******** to sun so eye-catching hair colors such as red and blonde could develop for the women while not having such negative consequences for the men. Whereas if a man had developed blonde hair in a place without much tree cover the glint of sunlight would give away his position from far away. The lessened ******** to sunlight also allowed eye colors such as blue and green whereas people are better off with brown in very sunny places.
In Africa, you've got a very warm climate, well, hot actually, and lots of sun ********. This leads to more melanin in the skin for protection and the penis has no need to retract into the body for protection either.
Obviously, when you're talking about so many people you can't make blanket statements but I think these are reasonable theories for the most part. Of course there will be asians who are showers and blacks who are growers because we've still got 99.906% of the same genetic makeup anyway.
As far as average penis size, many people seem to agree now that most men fall between 5"-6" inches with a girth of 4"-5.5". This is a lot smaller than previous studies and it's not like any truly random study with a decent amount of data has been done anyway.
You've also got factors such as guys who are bigger would be more likely to get involved with such a study, self-measurements, and the fact that growers lose more size than showers when not fully erect.
A bit of knowledge shouldn't hurt anyone's sexual fetish and fantasy. You can take in this information and still go back to enjoying whatever gets you off.