My family by blood consists of 4 people, my mother, father, and older sister. All of them have black or dark brown hair and brown eyes, but me. I am the lone redhead with blue eyes in the family. That means there were plenty of jokes about my real father being the milkman from people who either didn't study or remember junior high-level human biology, or who simply thought that the joke was just too funny to let knowledge interfere with the potential guffaws as they displayed their sparkling wit via cliché humor.
For those who have blocked out the knowledge of rudimentary genetics which explains my family's physical disposition (or who just slept through it all to begin with), I'll mention that there are dominant and recessive genes. How these things work is rather complicated, but the way in which the concept is introduced to us in school is by talking about things like hair and eye color and explaining why there are more brown-haired and brown-eyed people in the world and fewer blonds, redheads, and green and blue-eyed people. Light hair and eyes are recessive traits (or so I was told) and if the genes for both light and dark hair and/or eyes genes are present, the dark characteristics will manifest.
In order to have a progeny with blue eyes or red hair, each parent must have a recessive trait's gene (such as red hair) and only pass on the recessive ones. So, my parents had the genes for both types of characteristics and passed the dominant ones on to my sister, but the recessive ones on to me. If the child has brown hair and blond hair genes, the child will have brown hair. So, the formula works out such that there's a greater probability of any person having dark hair and dark eyes, though the entire situation is probably about a thousand times more complex in the real world, but, trust me that the milkman did not have to be my father in order for me to be the lone person with light hair and eyes.
Lest you think this post has to do with educating you with my crude understanding of genotypes and phenotypes (and yes, I remembered those words from decades ago when I originally learned them and didn't pick them up from current research - hooray for the American education system), let me reassure you that my intention is to raise what I felt was an interesting cross-cultural difference.
This morning I was discussing blood type and personality with a student and asking her if she felt things like hair and eye color influence personality. For those who don't know, the Japanese believe blood type has a role in shaping character. It's always been my opinion that Japanese people hang personality traits on blood type because they are physically so much more similar than western folks. We can say a blond is dumb or a redhead temperamental, but they've all got dark hair. They have to go deeper than the surface to form their theories.
During the course of our discussion, my student asked me if there were more blond-haired, blue-eyed people than dark-haired people back home. I told her there were not and explained to her the whole dominant-recessive lesson we were taught in biology as the reason for this. At first, she was a little puzzled but then she had a moment of total understanding. She told me that Japanese kids learn the exact same lesson about dominant and recessive characteristics, but that they are taught that information using a different example as the basis for that information...can you guess what that might be?
To me, this is a fascinating reflection of each culture's residents' physical composition and the effect it has on their personality theories and educational methods. To you, well, perhaps it's just an interesting bit of trivia.
If you couldn't guess, the answer was: Blood type.