Finger Length Predicts Agression in Men

Basically, they found relation between 2d:4d ratio of fingers, and violence/agression…

Finger Length Predicts Aggression in Men | LiveScience

“Finger lengths explain about 5 percent of the variation in these personality measures, so research like this won’t allow you to draw conclusions about specific people. For example, you wouldn’t want to screen people for certain jobs based on their finger lengths,” Hurd said. “But finger length can you tell you a little bit about where personality comes from, and that’s what we are continuing to explore.”