You may have heard that the more symmetrical a person’s face and body are, the more attractive he is considered to be, perhaps because symmetry suggests good genes. And indeed, matching hands bode well: A man whose left and right fingers match up is apt to have faster and more plentiful sperm than one whose fingers don’t match . Another study found that men with mismatched hands reported being depressed more frequently .
The lines on hands may also provide clues about early development. It’s well known that people with Down syndrome and people with fetal alcohol syndrome, as well as children of women who had measles while pregnant, are more likely than other people to have a “simian crease,” a horizontal line stretching from one edge of the palm to the other. In addition, although the overall research is not conclusive, some studies suggest that abnormal fingerprint patterns, such as those with a higher-than-average number of certain whorls, arches, or ridges, appear disproportionately among people with schizophrenia  and people who develop diabetes in middle age , possibly signaling a gestational disruption such as maternal illness. And males are more likely to have abnormal fingerprint patterns than females are—perhaps, researchers have suggested, because male embryos are more vulnerable to environmental influences .
Speaking of fingerprints, one study found that people who consume large amounts of salt and preservatives leave sweatier, saltier prints that are more likely to corrode certain metals, and thus are easier for detectives to pick up off, say, a bullet . For lawbreakers who love junk food, this finding may be the most predictive of all—at least when it comes to where they will be living for the next five to 10 years.
 Ferdenzi et al., “Digit Ratio (2D:4D) Predicts Facial, but Not Voice or Body Odour, Attractiveness in Men” (Proceedings of the Royal Society B, April 2011)
 Giffin et al., “Varsity Athletes Have Lower 2D:4D Ratios Than Other University Students” (Journal of Sports Sciences, Dec. 2011)
 Choi et al., “Second to Fourth Digit Ratio” (Asian Journal of Andrology, July 2011)
 Klimek et al., “Digit Ratio (2D:4D) as an Indicator of Body Size, Testosterone Concentration and Number of Children in Human Males” (Annals of Human Biology, April 2014)
 Collinson et al., “Increased Ratio of 2nd to 4th Digit (2D:4D) in Schizophrenia” (Psychiatry Research, Aug. 2009)
 Wu et al., “The Ratio of Second to Fourth Digit Length (2D:4D) and Coronary Artery Disease in a Han Chinese Population” (International Journal of Medical Sciences, Sept. 2013)
 Manning et al., “The 2nd to 4th Digit Ratio and Autism” (Developmental Medicine and Child Neurology, March 2001)
 Martel et al., “Masculinized Finger-Length Ratios of Boys, but Not Girls, Are Associated With Attention-Deficit/Hyperactivity Disorder” (Behavioral Neuroscience, April 2008)