Fingerprints can unlock phones, establish identity and even aid in diagnosing some congenital conditions, but how they form has long remained a mystery.

Now, a paper in the journal Cell reports that scientists have cracked the code — thanks in part to mathematician Alan Turing.

At around the 13th week in the womb, ridges begin to spread outward from three spots: at the center of the fingertip pad, under the nail and at the crease.

Like ripples around rocks dropped in a pool, they then spread and merge.

The unique patterns of arches, loops, whorls and Y-shaped junctions arise from the interplay of three signaling molecules: One, WNT, causes cells to multiply, form ridges and make the second molecule, EDAR, which boosts the activity of the first. The third molecule, BMP, pumps the brakes.

The signaling pattern follows a system proposed in the 1950s by Turing, who also studied theoretical biology. His reaction-diffusion theory described patterns in nature in terms of chemical interactions and spread patterns. In practice it explains only some observations.

The researchers tested the hypothesis by varying the signaling molecules in mice, which lack fingerprints but have toes with striped ridges that form similarly. They then used computers to model the how the interactions would likely affect fingerprint formation.  

The give-and-take of the signaling molecules also drives other processes in the skin, such as hair follicle formation and patterning.