We use easily measurable physical markers in order to test for the impact of neural structures on social preferences in a lab experiment and find large and significant effects. Subjects participated in standard trust, ultimatum and dictator games. We then gathered information on their index to ring finger length ratio and handedness. The finger ratio is a marker for prenatal testosterone exposure, which has important organisational effects on the brain, while left-handedness is associated with strong differences in brain lateralisation. We find that both markers are strongly and significantly correlated with behaviour in the social preference games with the effects of left-handedness going in the same direction as the effects of low testosterone exposure. These results are in accordance with current knowledge about the effects of prenatal testosterone exposure and handedness on brain structures and subsequent impacts on behaviour.