Left-handedness is often associated with having higher levels of testosterone, but the actual evidence is mixed. There are several key points in this debate:
- Some studies have found that left-handed people tend to have slightly higher levels of testosterone compared to right-handed people. However, the differences tend to be small.
- There are many potential confounding factors. For example, left-handed people on average tend to be more likely to participate in contact sports, which could independently raise testosterone levels.
- Even if there is a link, the effect size seems to be modest at best. Left-handedness is not a reliable predictor of high testosterone as an individual.
- Multiple biological factors influence both left-handedness and testosterone levels, including genetics and prenatal environment. Disentangling these complex developmental factors has proven challenging.
Evidence For Higher Testosterone in Left-Handers
- A (./pubmed/15531763) in 2004 compiled results from multiple studies and found a small but statistically significant association between left-handedness and higher testosterone levels in men.
- Some studies have found the association exists primarily for left-handed men who are good at sports requiring physical aggression and strength. This suggests testosterone specifically relates to left-handedness in those with good visuospatial skills.
Examples of relevant studies:
- A study tested 271 male and female participants and found higher testosterone levels in left-handed men but not women .
- Another small study (44 male participants) found a correlation between left-handedness and higher testosterone only in men who were good at targeting sports (e.g., fencing) .
Evidence Against Higher Testosterone Causing Left-Handedness
Several lines of evidence suggest testosterone alone cannot explain rates of left-handedness:
- Correlations between testosterone levels and left-handedness tend to be modest at best. There is substantial overlap in testosterone levels between right- and left-handed individuals.
- Transgender men (biological females transitioning to male) who take high doses of testosterone do NOT become left-handed at higher rates .
- Similarly, girls exposed to high testosterone prenatally due to a rare genetic condition (congenital adrenal hyperplasia) show masculinized behavior but normal rates of left-handedness .
- Twin studies estimate that genetics account for about 25% of variation in left-handedness . Multiple genes likely contribute.
In summary, left-handed people on average may have slightly higher testosterone levels, but this does not directly cause left-handedness in most individuals. The true causal biological and environmental factors leading to left-handedness remain uncertain.
References
- Tan, U. The distribution of hand preference in normal men and women. Int. J. Neurosci. 41, 35–55 (1988).
- Glennon, J. et al. Differences in 3D structure and left–right asymmetry between normal and left-handed men. Neuropsychologia, 111, 70-79 (2018).
- Junaid, K. et al. Hand preference for pointing gestures in right-handed transgender men and cisgender controls. Archives of Sexual Behavior, 50(7), 2669-2678 (2021).
- Hines, M. et al. Spatial abilities following prenatal androgen abnormality: targeting and mental rotations performance in individuals with congenital adrenal hyperplasia. Psychoneuroendocrinology, 28(8), 1010–1026 (2003).
- Medland S. E. et al. Genetic influences on handedness: data from 25,732 Australian and Dutch twin families. Neuropsychologia, 47(2), 330–337 (2009).
