Does your hand look like my wife’s hand? Do your fingers fold down along two major lines, a distal and proximal crease? Most human hands do, but for about 15 percent of the population it’s not that simple. For example, on my left hand, my distal crease fuses with my proximal crease, creating a single fold line all the way across my hand. On my right hand, a bridge crease connects both lines, meaning that my hand folds again along just one fold line. They’re sometimes called Simeon lines; I guess because they make your hands look like little monkey person hands. Medical professionals tend to just call them single traverse palmer creases if they refer to them at all.
The major creases of the palm have not shown to have much predictive power when it comes to health or medical issues; they’re just kind of random, like fingerprints. Fingerprints freak me out; there are swirls and loops formed at random in the womb, not according to instructions from your DNA, so identical twins may have the same genome but they won’t share the same fingerprints.