The ratio of the second to fourth digits on a hand may be affected by early exposure to androgens.
Finger length measurements are taken on the ventral (palmar) side, from the tip to the crease at the base of the digit in its midline. Each measurement is taken twice and the average used.
(1) length of left second digit in mm
(2) length of left fourth digit in mm
(3) length of right second digit in mm
(4) length of right fourth digit in mm
ratio of left second to left fourth finger =
= (length of left second finger in mm) / (length of left fourth finger in mm)
ratio of left second to right fourth finger =
= (length of right second finger in mm) / (length of right fourth finger in mm)
directional asymmetry =
= (ratio of left second to fourth finger) - (ratio of right second to fourth finger)
• In males the ratio for the right fingers tend to be lower than for the left fingers.
• The directional asymmetry is a positive number for typical males. The directional asymmetry correlates with serum testosterone levels.
• A woman with a positive directional asymmetry may show greater reactive aggression.
• Accurate measurement of the digit lengths is essential since the differences are small.
• The basal crease of the second digit has a definite angle, so determination of the midline is important.
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