Hand preference in humans is associated with testosterone levels and androgen receptor gene polymorphism

► Studied testosterone levels and androgen receptor genotype in left-, right-, and mixed handers. ► Strongly left-handed men were found to have lower testosterone than right-handed men. ► Weakly left-handed men ('mixed' handers) showed DNA evidence of a less active androgen receptor. ► Findings support theories suggesting handedness differences in testosterone exposure. ► Findings may offer a way to unite endocrine and genetic theories of handedness.