How do human fingerprints form?

[Magical Realist]

And what makes every set unique? Is it in our genes? Do twins have the same fingerprints? Are toe prints unique too?

 

[C C]

And what makes every set unique? Is it in our genes? Do twins have the same fingerprints? Are toe prints unique too?

Despite plenty of research, there is no broad consensus on any particular explanation as to how epidermal ridges on palms, fingers and soles arise.

Below the outermost layer of the skin (epidermis) is the dermis. The interface to the latter is the basal layer and features column-like cells which are at a right angle to the skin surface. Around the 10th to 13th week of pregnancy the basal layer becomes undulated / wavy and soon draws "valleys" or depressions of the outer layer into the dermis. These primary ridges are a template for the future surface pattern, which is established circa the 16th week. Superficial skin injuries are unable to eradicate fingerprint patterns because of their being encoded between the dermis and epidermis.

A traditional hypothesis for their "evolutionary use" was that such ridges improved grip. But apparently there is newer research which suggests that they may actually reduce friction. Feeding contrarian beliefs among scientists that they instead improve sensitivity or help cast off sweat (koala bears, however, feature prints but lack sweat glands).

The differing uterine environments and chemical exposures of monozygotic twins contribute to their development, not just genetic factors. While some aspects of fingerprint patterns might be inherited from parents, the latter's varying DNA combinations among ordinary siblings, along with the aforementioned womb influences, ensure their uniqueness.

While toe prints could likewise be employed to identify culprits in crime, their elongation usually results in only fragments being available. Obviously there is also no significant national database for toe prints, either.

 

[wegs]

Interesting thread, Magical! I like this website: http://science.howstuffworks.com/fingerprinting1.htm
Fingerprints are even more unique than DNA.
According to this site info, there's a one in 64 billion chance that your fingerprint will match up exactly with someone else's.

 

[GeoffP]

Presumably... and this is interesting, actually... it might be a semi-randomized process. Presumably, local switches for epidermal growth are activated and cascade laterally (so that you get a "ridge"). Thus I guess only "semi-randomized".