2D:4D finger length ratio
Anyway it turns out that a bunch of interesting studies have been done on this and all kinds of fascinating results have been found. In all cases I will try to describe the results based on the perspective of having a lower ratio(ie. significantly longer ring finger than the index finger), which is considered generally to be associated with more masculine traits. Here is a taste of what the research suggests:
Men with a lower ratio correlates with more Physical Aggression
Better asymmetrical hand performance in Jamaican children
Across ethnic groups Afro-Caribbean blacks have the lowest ratios, with Oriental Hans having the highest
Low ratios correlates to larger families for men, whereas high ratios correlate to larger families for women
Lower ratios correlate with a lower likely hood of homosexuality.
A lower ratio correlates to better performance in skiing
It also correlates with a better ability to play soccer (football outside the US).
Increased likely hood to be a "butch" lesbian versus a "femme" lesbian among self-described lesbians
Lower ratios suggest a higher likelihood to have Autism and possibly Asperger syndrome
There are lots of interesting available abstracts on the National Library of Medicine . Just search their PubMed website for "2D:4D ratio" there were 47 abstracts when I did it today.
Bonus: An interview with the scientist that did the study on soccer players