Don't it make ...

my brown eyes blue. According to this story from today's Boston Globe, blue eyes have become much less common over the past century or so.

If the Census Bureau has it right, the 300 millionth American entered the United States kicking and screaming this morning. The odds are that this milestone American is a boy, born to a white family in a California suburb. He will have a 1-in-4 shot of graduating from college, will probably marry, father two children, struggle with his weight, and live to see his 85th birthday.

What he will probably not have -- that his grandfather likely did -- is a pair of blue eyes.

So what explains today's lack of blue-eyed folks? While many factors probably played a role, changes in marriage patterns in the last few decades may have been the biggest cause.

About half of Americans born at the turn of the 20th century had blue eyes, according to a 2002 Loyola University study in Chicago. By mid-century that number had dropped to a third. Today only about one 1 of every 6 Americans has blue eyes, said Mark Grant, the epidemiologist who conducted the study.

A century ago, 80 percent of people married within their ethnic group, Grant said. Blue eyes -- a genetically recessive trait -- were routinely passed down, especially among people of English, Irish, and Northern European ancestry.

According to Grant, by mid-century, education level rather than ethnic group became the primary factor in selecting a spouse. Since education was becoming more "diverse", blue-eyed folks began marrying outside their own blue-eyed groups. Since blue eye color is a recessive trait (100% chance of "pass along" if both parents are blue-eyed, 25% chance if a blue mates with a brown), this led to the decline of blue eyes and the emergence of brown.

As I read this, I thought, "How cool." Then I began to wonder if the "ideal" of the blue-eyed beauty might be based on an ancient preference for someone who was ethnically pure. Turns out, there might be something to that.

Preferences for fair skin and blue eyes stretch back in Europe to at least the Middle Ages, according to Hema Sundaram , author of ``Face Value," a book about the history of beauty. For women in particular, especially those of European descent, fair skin and light eyes have long been seen as indicators of fertility and beauty.

As society has changed, however, beauty ideals may be changing too. While blue remains, by far, the most popular fake contact color, it's losing market share (down from 53 to 45%) to brown (up from 8 to 15%).

I'll admit that I can see no practical use for this in a "how can we make the world a better place" role, but I love the fact that people think about and investigate such things.

Actually, if you read the whole story you'll see this is a prime example of the "scientific method". The researcher became interested in eye color after he noticed that his elderly patients in nursing homes had much higher levels of "blue eyedness" than the general population. He hypothesized that blue eyes might have some link to longevity, but it turned out to be an omitted variable type problem. To me, this is a good example of research: The data did not support his original hypothesis, so he looked for an alternative explanation. Unfortunately it seems the more common approache is to "massage" the data or your model until they do support your hypothesis. Oh, that reminds me of a potentially bad use of data I read about today -- a new study showing a link between autism and television viewing among children -- but that'll have to wait until I have time to think about it a little more. Can't wait, can you?