Some, if not most of us, have four fingers and a thumb. I have questions regarding those that have more than this:
Due to routing of tendons etc. Most of us (quintdactyal(?) folkes) can’t move our little finger without it also moving our ring finger. Is this universal. Does the little finger automatically affect the one next to it.
I’m guessing “it depends” - Some fingers may be residual but do Polydactyls have independent movement. Duplicated Muscles - Duplicated tendons - Duplicated nerve pathways (both movement and independent touch etc)?
Most cases of polydactyly are vestigial with a few that are more fully formed but still non-functional. I see them commonly hanging off the little finger, and a few times as a partly duplicated thumb or Great Toe. But there are rare cases of functional supernumerary digits, even if I’ve never seen it.
Here’s a case report of a mother son dyad with functional bilateral supernumerary fingers between thumb and index finger.
If you can both fully flex your little finger without your ring finger moving we have a very unusual group of people here.
It is generally accepted that such does not typically occur. The following article is an attempt to parse out how much of that standard lack of full independence is mechanical coupling and how much limitation imposed by neuromuscular control.
Fully flex? Like curl it to the palm? No. But holding it straight, i can move it forward and back, it and side to side, without moving the ring finger.
Curiously, i can curl the other three fingers independently.
I just checked and I can move both little fingers in all directions and curl and flex independently of my ring fingers. Is it really all that unusual? Speaking of guitar, I do play, though amateurly. Maybe that helps?
Yes that is my understanding, to some degree just because of how the tendons cross connect.
Please note the phrase is completely independently. Fully flexing the little finger to palm without the ring finger moving at all, or fully move the little finger to the side as far as it goes without the ring finger following it some. Only moving a small range, or the other finger only moving a small bit, is not complete independence.
It’s certainly possibly to do it. Right now i am holding my phone with the ring and middle finger on one side, and the thumb and palm on the other. And with the ring finger held in place, it’s easy to move my little finger around, in almost it’s full range of motion. I can even bring it to the palm. But if i try to flex the joint closest to the fingernail, i have to be very careful, or everything cramps. (I can do it, but if i move in the wrong order it’s unpleasant.)
I mean, does moving one finger tend to tug another because they are connected? Yes. Does that mean it can’t be done? No.
Oh, interesting. My left pinky has a much smoother and more controlled motion than my right pinky.
I can move my right little toe outward independent of my next (ring?) toe, but my left little toe I can not move independently at all. Always though that was weird that it wasn’t bisymmetrical.
Holding the other finger still is “cheating” here; the point trying to be made is that the tendons are connected so that if the ring finger isn’t being held still by an outside influence, it will move along with the pinky.
It’s not difficult to do when the other fingers are braced against an object or each other. Doing it it with the hand held in mid-air, without any other fingers touching each other or anything else is what’s being asked about.
I think I must be failing to explain what independent movement is that so many here are believing they can do what is documentably … not common.
Anyway. The OP was more about functional polydactyly. I may weird (okay, independent of this, I am) but I think that kindred with bilateral functional fingers between their index and thumbs is very interesting to consider.
I am a bit frustrated that the report was not more complete.
There is a huge chunk of brain real estate devoted to both sensory and motor control of the thumb and index fingers.
Did the region devoted to control of those supernumerary digits cannibalize from that region, did the real estate devoted to the hand overall enlarge, harvesting from something else?
Did the region become more active and functionally more densely packed?
I know it’s not quite the same thing but it makes think of this as a connection-
Early inputs, different than what the brain was precisely evolved for, can repurpose functions in the brain. Be it reallocating motor cortex to serve six digits instead of five, or visual cortex responding to somatosensory input.
In both cases early, during periods of brain plasticity, seems important.
