十万个为什么·科学启蒙30篇（2）

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人类为什么有指纹？

Fingerprints form before birth — around weeks 10 to 24 — as skin layers grow at different rates, causing ridges to buckle under tension.
These patterns aren’t random; they’re influenced by genetics, amniotic fluid pressure, and even fetal movement — making each person’s prints unique.
Ridges improve grip on rough or wet surfaces by channeling water away and increasing friction, much like tire treads on a car.
They also enhance touch sensitivity: ridges amplify vibrations when sliding over textures, helping nerves detect fine details like fabric weave.
No two people — not even identical twins — share identical fingerprints, although family members may show similar pattern types like loops or whorls.
Forensic analysts compare ridge endings, bifurcations, and other minutiae rather than whole patterns, since partial prints are what crime scenes usually yield.
Some rare genetic conditions, like adermatoglyphia, cause people to be born without fingerprints — proving they aren’t essential for survival.
Modern biometric systems use infrared or ultrasonic scanning to map ridge depth and sweat pore placement — not just surface images.