It's one of the most common questions in forensics: identical twins have identical DNA, so surely they have identical fingerprints? In fact they don't — and the reason is a neat illustration of how fingerprints are made.
Same DNA, different fingerprints
Identical (monozygotic) twins come from one fertilised egg and share essentially the same genome. Their fingerprints are similar — often the same general pattern type — but they are not the same, and an examiner can tell them apart.
Why: genes set the stage, chance writes the detail
Genetics influences the broad pattern of ridge skin, but the fine detail — the exact positions of ridge endings and bifurcations — is shaped during development in the womb by random physical factors: the flow of amniotic fluid, the fetus's position and movement, pressure, and timing. These micro-environmental influences differ even between twins sharing a womb, so each finger ends up with its own unique minutiae.
Why this matters
The twin case draws a sharp line between two kinds of evidence:
- DNA — inherited, so identical twins share a standard profile and cannot normally be separated by it.
- Fingerprints — shaped by developmental chance, so even identical twins are distinguishable.
That's why, in the rare cases where DNA can't separate two suspects who are identical twins, a fingerprint (or other non-genetic evidence) can. Far from a weakness, the fact that fingerprints aren't fully determined by genes is exactly what makes every finger — on every person — unique.