Part of the problem is the term that is commonly used: 'identical' twins. The correct term is 'monozygotic', meaning that 'derived from a single egg'. In line with this, so-called 'fraternal twins' are better described as 'dizygotic' (from two eggs). Monozygotic twins result from a single fertilization event and are fairly rare (about 3 in every 1000 births). Monozygotic twins, although genetically very similar, are not genetically exactly the same. Furthermore, even within the womb, the foetuses touch different parts of their environment, giving rise to small variations in their corresponding fingerprints and thus making them unique.

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