One of the most intriguing segments of the show was a race of 6 elite male runners.  The scientist in charge of this one was someone who studied finger lengths -- specifically, the ratio between the index finger, or second digit (2D) and the ring finger (4D).  This was his index for testosterone exposure in utero.  He theorized that the runner with the lowest 2D:4D ratio (ring finger longest) would win.  He made a photocopy of each runner's palm (face down), and then used calipers to very carefully measure the length from the crease where the finger meets the palm to the tip of the finger.  Before the race, he predicted the finishing order without knowing anything about the runners (e.g., training regimen, diet, health history) except their 2D:4D ratio.  I couldn't believe how excited I got by that race!  And his predictions were right, except he mixed up the 3rd and 4th place winners.

Other scientists have studied this ratio as well.  A British study found that males with a "female" 2D:4D configuration (e.g., longer index finger) made better scientists and were less likely to have kids, while women social scientists had more "male" 2D:4D patterns (e.g., longer ring finger).  Aggression levels in males, but not females, has been divined from finger length.

Another studyfound that the ratio could predict students' SAT performance:

Kids with longer ring fingers compared to index fingers are likely to have higher math scores than literacy or verbal scores on the college entrance exam, while children with the reverse finger-length ratio are likely to have higher reading and writing, or verbal, scores versus math scores.

Younger kids have been studied, too:

A recent study of digit ratio in Scottish preschool children between the ages of 2 and 4 found strong relationships between digit ratio and gender-normative behavior. Girls with masculine-type finger ratios tend to have higher hyperactivity scores and more problems relating to their peers than do other girls. The same study, published in Early Human Development, found that boys with female-type finger lengths are on average more emotional than other boys. "They tended to be very sensitive," says Manning.

The higher incidence of autism among boys than girls also led to some research in that area, and the early findings are that one-year-olds with longer ring fingers fared worse on tests of language skills and willingness to make eye contact. (Of course, the vast majority of boys with typical testosterone levels don't have autism.)  Other studies have suggested that female homosexuality (but not male) can be predicted by a low 2D:4D ratio

Some scientists believe prenatal sex hormones are also part of the puzzle of homosexuality and that a high level of testosterone may wire the brain for attraction to the same sex. Intriguingly, research shows that a prenatal testosterone level is most strongly linked to homosexuality in women, according to a recent article in the Archives of Sexual Behavior. Lesbians are more likely than straight women to have a masculine finger ratio, says McFadden.

A more "female" pattern (high 2D:4D) is correlated with increased risk of both breast cancer and depression.

Not everyone believes that uterine hormones explain the finger length differences; one twin study suggested that genetics were much more explanatory than the uterine environment.  So I think the real scientific jury is out on whether the finger ratio theory is connected to anything real, and what causes the finger ratio.  

Still, ever since my interest was piqued, I've been informally checking out people's fingers lengths.  My own (2D significantly longer than 4D) seems to square with my experience of having better verbal than math skills and being prone to depression.  My DS's ratio looks to be about 1.0, which goes along with his collaborative nature.  (He had a blast playing paintball yesterday, but he talked more about how his team worked together than he did about beating the other team). DH has a typical male ratio, and he seems to like "guy" stuff well enough, with the usual exceptions (for example, this weekend he worked on the electrical to install a new chandelier, but not until he had finished his coffee served in a dainty teacup -- with a saucer).  

I'm always curious to get more data points on this stuff, just for fun.  So please, take the poll and use the comments to tell about how this does or doesn't hold up in your life.  I think I can edit the poll (?) if more options are desired.  And I hope I haven't offended anyone -- I don't want to be sexist or suggest that any ratios or personality styles or career choices or sexual preferences or number of trophies are better than any others.