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If you want to check it out, lay your hand flat on a table with the palm facing upwards, then touch together your thumb and pinky finger, raising your hand slightly off the surface as you do so.
Can you see a raised muscle or tendon sticking up in the middle of your wrist as you do that?
Well, if you can, you're one of the majority, and you still have a palmaris longus.
If you can't, you're among the 14 or 15 percent of people who don't have one.
Why is this interesting? Well, it helps to show the evolutionary progression of man, for starters.
The palmaris longus is a muscle that you can find between the flexor carpi radialis and the flexor carpi ulnaris - if you know what either of those things are - and it is not present in all humans.
It is found in many different types of apes, but is particularly long and prevalent in those that still use their hands to fling themselves around a bit using their arms.
That means that we've no real use for it anymore really and some of us simply no longer have one.
The same goes for chimpanzees and gorillas, who - like us - don't spend that much time in the trees either.
Lemurs and orangutans, for example, still use theirs quite a lot.
Humans seem to have inherited the muscle through common descent through evolution from other primates, who might have used the palmaris longus loads.
As we continues to evolve and develop, we started to employ our thumbs more and more, and the thenar muscle group, and therefore the palmaris longus became vestigial.
Because there is no evolutionary pressure on the muscle, which is to say that it has no impact on us whether we have it or not, most people just haven't got rid of it.
Whether you've got it or not, it has no effect on your grip strength, as it has no function anymore.
Interestingly enough, the amount of people who lack this particular throwback body part varies vastly around the world.
Depending on where you live, or what your ethnicity is, there are massively fluctuating statistics regarding whether you'll have it or not.
Even the form that it takes can change, as some differences in the make-up and relationship between muscle and tendon have been observed around the world.
Oh, and some people only have one, whereas others have two
Fascinating stuff, really.
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