If you are a twin, at one of your follow-up visits you obtained (or will obtain) a score of how much your fingerprints vary from your twin’s fingerprints. Read on to see how we found this score.
During your first visit to the MTFS labs, one of the measures we obtained to determine whether you are identical or fraternal twins were your fingerprints. The distinctive arches and loop patterns of your fingerprints form during the fourth month of fetal life. They are mostly determined by heredity and a little by the environment in the womb, so they tend to be good indicators of similarity. From your fingerprints we counted the total number of ridges on each of your fingers to get what is called a “ridge count.” The Slater’s Z-score below combines both you and your twin’s fingerprint ridge counts and then compares how similar or dissimilar they are to each other. Since your score represents how much your fingerprints vary, low scores between .01–.60 indicate similar fingerprints; identical twins usually have scores in this range. Scores from .40–1.50 typically correspond with fraternal twins because they indicate fingerprints that are quite different. The scores of identical and fraternal twins overlap sometimes, resulting in pairs of identical twins who have higher scores (more differences) than the average set of fraternal twins. If your score isn’t what you expected, keep in mind that your Slater’s Z-score is not conclusive; it is only one of the eight measures necessary to determine whether you are identical or fraternal.