Palmaris Longus
From Wikipedia:
The palmaris longus is a muscle visible (in humans) as a small tendon between the flexor carpi radialis and the flexor carpi ulnaris - but - it is not always present. It is absent in about 14 percent of the population; however, this number varies greatly in African, Asian, and Native American populations. Absence of the palmaris longus does not have any effect on grip strength. The palmaris longus muscle can be seen by touching the pads of the fourth finger and thumb and flexing the wrist (upwards). The tendon, if present, will be visible in the mid-line of the anterior wrist.
The palmaris longus is a muscle visible (in humans) as a small tendon between the flexor carpi radialis and the flexor carpi ulnaris - but - it is not always present. It is absent in about 14 percent of the population; however, this number varies greatly in African, Asian, and Native American populations. Absence of the palmaris longus does not have any effect on grip strength. The palmaris longus muscle can be seen by touching the pads of the fourth finger and thumb and flexing the wrist (upwards). The tendon, if present, will be visible in the mid-line of the anterior wrist.
Notice at the "X".
bob
The muscle is present in the wrist on the right - it is missing on the wrist on the left.
Wikipedia continues:
The evolutionary interpretation of the muscle's absence is fairly simple. Humans inherited the muscle through common descent, and numerous animals that we share a common ancestor with (such as the orangutan) still actively employ the muscle. Close primate relatives (such as the chimpanzee and gorilla) also do not actively employ the muscle, and hence they also demonstrate the same variability. The common descent principle suggests that at some stage our ancestors employed the muscle actively. The primate branch then began to evolve the thumb apparatus (and particularly the thenar muscle group) and consequently the Palmaris longus became vestigial. As there is no apparent pressure (positive or negative) concerning the muscle, evolution has largely left it alone. Its persistence might possibly be due to the fact that the necessary changes to the gene(s) involved in losing the muscle may have other consequences, but this is only speculation.
Several years ago, when a bunch of my family members were gathered, I looked for this tendon in each of them - of the 10 of us present, 2 did not have it, the rest did. I myself do not have the tendon.
Wikipedia continues:
The evolutionary interpretation of the muscle's absence is fairly simple. Humans inherited the muscle through common descent, and numerous animals that we share a common ancestor with (such as the orangutan) still actively employ the muscle. Close primate relatives (such as the chimpanzee and gorilla) also do not actively employ the muscle, and hence they also demonstrate the same variability. The common descent principle suggests that at some stage our ancestors employed the muscle actively. The primate branch then began to evolve the thumb apparatus (and particularly the thenar muscle group) and consequently the Palmaris longus became vestigial. As there is no apparent pressure (positive or negative) concerning the muscle, evolution has largely left it alone. Its persistence might possibly be due to the fact that the necessary changes to the gene(s) involved in losing the muscle may have other consequences, but this is only speculation.
Several years ago, when a bunch of my family members were gathered, I looked for this tendon in each of them - of the 10 of us present, 2 did not have it, the rest did. I myself do not have the tendon.
Some people have the tendon in one wrist but missing in the other.
This is just one more evidence for human evolution - or - it is evidence that during the creation process God decided to give most humans an unnecessary tendon, and for the rest he decided not to include it in the ingredients?
This is just one more evidence for human evolution - or - it is evidence that during the creation process God decided to give most humans an unnecessary tendon, and for the rest he decided not to include it in the ingredients?
bob
r.u.reasonable@gmail.com
I had never heard of this vestigial remnant before. And I've read Dawkins and Coyne's book's on evolution, for the layperson. Fascinating stuff.
ReplyDeleteI just checked and I don't have the tendon. I checked my partner, and she does. Everyday is a learning day.