The length of a man's index and ring fingers have recently been linked from everything to promiscuity and how nice he is to women. The idea is that finger lengths change depending on exposure to testosterone in utero, and it's known as the "2D:4D" ratio. A lower ratio—where the second digit is shorter than the fourth—indicates "greater androgen exposure." In the journal Clinical Anatomy, researchers write that others have previously suggested a link between androgen exposure in the womb and schizophrenia; they take that one step further, hypothesizing the ratio could be predictive of schizophrenia in males. Then they set out to test that hypothesis: In their small study, researchers analyzed the finger lengths of 103 Turkish male patients diagnosed with schizophrenia and 100 healthy male controls.
They found "significant differences between schizophrenia and control groups concerning the ratio ... in both hands," the researchers report in a press release. The findings occupy opposite ends of the spectrum: The right-hand 2D:4D ratio was "significantly higher" among the schizophrenia group and the left-hand ratio was "significantly lower"—suggesting the two are opposites, perhaps because testosterone "affects finger ratios differently as it acts in different ways on the left and right hemispheres of the brain," per the study. As for those ratios, the researchers found the size of the ratio in the left hand could indicate the severity of negative symptoms in patients. (A recent study found that schizophrenia isn't actually one disease.)