I have read factual studies that suggest size can decrease with ethnic mixing.
There was a European study that found pure bred Norwegians to average half an inch longer than those who had mixed with other races. (No this isn't meant to be a racist comment). Thats an 8% difference. Doesn't sound like much, but if I were 8% shorter in height I would 5'-6" tall instead of 6'.
That is a lot for an overall average.
Hmm interesting study but I wonder what is the confidence level of these results, how big are the sample sizes, how do they select their candidate for survey, measuring techniques etc. There is no such thing as as pure bred Norwegian nowadays anyway, almost all Norwegians are mixed with the Sami people, if not Swedish, Danes, or Finns. Well that is of course unless the study was done prior to 1100s just before the Norsk start mixing with the rest of Europe.
I go to a school with 80% of the pupil are Norwegian nationals, but I don't think there is one who will truely call themselve a 'pure bred'. Have you ever seen the book 'Penis Atlas" by Norwegian Sexologists Esben Esther Pirelli Benestad, et al? I have a copy at home, and all the specimens they have in that atlas is supposingly as Norwegian as you can get, but I was a bit dissapointed to find out Norwegian seems to be in the rather small scale (the smallest they have in the sample is like 1" and the biggest is only about 8") and funny thing is the 8" was Norwegian of mixed race (mix with black I think)
Im one truly mixed race here, Im as mix as one can get, people talk about racism, but I find the racism towards half caste or more mix people even alot harsher with names like mud, mongrol etc. These studies is of course interesting, but the basis of the reasoning of this study is rather racist, and hence could be very biased as well if the way the sample their sources or conduct their study. But be interesting if you can tell us where did you read this study from, by whom it was conducted, etc? (words from grapevines are more powerful than facts sometimes)