A study by biomechanicist (apparently, there's such a thing) Roland Ennos and Peter Warman of the University of Manchester, UK, has just blown away decades of conventional knowledge: fingerprints do not increase our grip - instead, it reduces it!
Rather than singe the prints off an unlucky student to compare hands with and without prints, Ennos rigged Warman's fingers to a special device that slides a weighted sheet of Perspex across a finger and measures the resulting frictional force.
Ennos and Warman determined that the amount of friction generated went up as more of the fingerprint was touching the sheet, but not by as much as expected. This indicated that the skin was behaving like rubber, where friction is proportional to the contact area between the two surfaces.
So, if not for increasing grip, then why do we have fingerprints? Scientists think that fingerprints may improve tactile sensitivity, help water wick off fingers, and reduce shear stress.