As an example, see this study:
Finger-length ratios and sexual orientation
(Department of Psychology and Graduate Groups Neuroscience, Endocrinology, UCB)
Our results suggest that events before birth (or even before conception in the case of older brothers) influence human sexual orientation. The masculinized right-hand 2D:4D ratio in homosexual women may reflect fetal androgen levels that are slightly higher than in heterosexual women. Homosexual men without older brothers have 2D:4D ratios indistinguishable from heterosexual eldest sons, indicating that factors other than fetal androgen (such as genetic influences, ) also contribute to sexual orientation. Finger measures indicate that men with more elder brothers, including those men who develop a homosexual orientation, might be exposed to greater than normal levels of prenatal androgen.
.8. Bailey, J. M. & Pillard, R. C. Arch. Gen. Psychiatry 48, 1089-1096 (1991). Links
.9. Hamer, D. D., Hu, S., Magnuson, V. L., Hu, N. & Pattatucci, A. M. L. Science 261, 321-327 (1993). Links
A more layman's summary of the same study from BBC:
Scientists from California found that lesbian women have a greater difference in length between their ring finger and index finger than straight women do.
The same pattern was also found for homosexual men - but only when the researchers looked at those males that had several older brothers.
Please note that the study did not indicate direct causality, merely correlation, though it did propose a theory deriving the higher likelyhood of both traits (finger length ration and homosexuality) from the same underlying cause - fetal androgens.