There is a reason why you have lines on your palms and it has nothing to do with foretelling your future.
Your hands are the most hardworking part of your body and they are capable of several actions, including holding, stretching, lifting, typing and writing. To be able to do these different tasks and change their shape constantly, the skin covering them should be able to adjust itself to the complex positions. That is where the lines on your palms come into play. These lines are technically called creases, or palmar flexion creases to be more specific, and they are required to divide your palm into sections for flexion.
These creases help in folding the skin on your hand when you change its shape, say when you make a fist or bend your hands. If you did not have these creases, you would have loose skin hanging out from your palms under your fingers.
Take a look at the lines carefully and you will see that each one of them is at a place where your hand bends. The same goes for the lines on your elbow, knees, wrist etc. They prevent the skin from bunching up into clumps and provide an avenue for the skin to tuck into when your joints contract and then enable the skin to unfold when your joints extend. This is the reason why you have strong and prominent creases where the bones of your finger meet your thumb.
Babies develop these flexion creases on their hands when they are in the womb itself, at around the 12th week of gestation. The thickness and number of creases on the palms depends upon factors such as race and genetic history.
Most people have three prominent creases across their palms. Some people are also known to have a single crease, known as a simian crease, which indicates an abnormal development. Most doctors check the palms of a new born baby to check if the baby has a normal development. Simian creases are sometimes observed in babies with conditions such as Down syndrome, foetal alcohol syndrome or other genetic disorders.
In China however, a single palm crease is considered to be a normal phenotypic alternative, with around 16.8 percent of healthy newborns having unilateral single transverse creases and approximately 6.6 percent having bilateral single transverse creases.
Interestingly, a study conducted in Korea found that the union of creases is related to hand grip, whereas another report in France presented that hand strength can be predicted from the circumference of the hand. A third study combined the results of both the researches and concluded that people with a large hand circumference and fused hand lines such as the simian crease have greater hand strength.