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Sensorimotor Mechanics of People with a Sixth Finger (bps.org.uk)
71 points by sohkamyung 14 days ago | hide | past | web | favorite | 32 comments



The interesting technology of ctrl labs:

  https://www.ctrl-labs.com/
will give "common five fingered" individuals the ability to catch up.

They use machine learning to decode the nerve impulses in the arm, so you can play video games without moving and can let you synthesize "extra" arms.

search "ctrl labs" and watch the youtube videos, some of scifi possibilities are very interesting.


>suggest that it may be of value to augment normal five-fingered hands with an artificial supernumerary finger

That's missing the big picture in my opinion. This research indicates the human brain is capable, all on its own, of adapting to entirely new sensorymotor functions. Think of the implications. If some type of new functionality were grafted onto you, you'd be able to control it without having to "reassign" any of your current functions. You could move a "third hand" cursor around in three dimensional virtual space as if it were a virtual body part, not just an interface you have to consciously manipulate like a mouse or keyboard.


I'm not sure if we can think our brain will learn to control a new functionality, or as in the case of these people, it's only able to learn to use it if it's been there since the brain formation.

We don't know, at least by this study, if the brain can learn once it has developed.


> not just an interface you have to consciously manipulate like a mouse or keyboard

How conscious is that really tho? I don’t think about how to type, I just think thoughts and they come out on the screen. It’s about as conscious as speaking.

Same for the mouse. I don’t think about the mouse consciously, I just look at an item on the screen and choose to interact. Like grabbing a glass of water with my hand.


Now matter how perfect it is, it is by definition less perfect than the movement of your hand itself. The real world is also limited by inertia, which virtual interfaces are not if they bypass the hands entirely. We're a long way from developing really good brain-computer interfaces, but this finding means we have just a little less groundwork to lay.


We've actually known this for quite a while. And there are paraplegics controlling a normal 2D mouse with their brains right now. I'm not sure they ever attain the dexterity you or I manage by controlling a mouse with our hands, but it can be done. It can even be done without surgery now.

https://www.ncbi.nlm.nih.gov/pubmed/18367779


I remember reading (a long time ago so can't provide a reference) that in 1000s of years most humans would have an extra finger. I'd assumed that this was because of the evolutionary advantage it would have given their forebears, although I would question how much natural selection applies to rational beings like humans these days. But on a quick bit of reading now, it seems like it could be because it is a dominant trait. Although after a bit more reading, it seems it might not become more common over time due to the Hardy-Weinberg principle[0].

[0] https://en.wikipedia.org/wiki/Hardy%E2%80%93Weinberg_princip...


I know it was just an aside, but I can't let this go:

>I would question how much natural selection applies to rational beings like humans these days.

It's a universal principle, why wouldn't it apply? Each generation is composed of the offspring of those members of the previous generation who reproduced, introducing a statistical bias. Why would it be different "these days", and what has rationality got to do with it?

Besides - as for the notion of 'rational' humans, especially in the context of sex and reproduction - I'll get my coat.


> It's a universal principle, why wouldn't it apply?

Because ever since we've invented writing (and arguably even before that - ever since we've invented spoken language), we've left the domain of biological evolution. We now accumulate, evaluate and discard knowledge and technology couple orders of magnitude faster than natural processes. From nature's POV, the entire ~10k years of human civilization happened in a blink of an eye (and note that all the interesting things happened arguably in the last couple hundred years).


There is still differential production of offspring who produce offspring. The selection is against kind of people who have few children or have few children who go on to have children themselves. That’s how it always has been and always will be unless we abolish natural reproduction.


Again, whatever effect this selection has (with quantized increments of the length of a generation), it's completely drowned in memetic and technological evolution(s) which currently operate at the speed of Tweet. In your particular example, this arguably derails biological evolution completely - the decision to have kids, and how many kids to have, is dominated by economic and (secondarily) cultural considerations, which change significantly between generations. Evolution will have hard time identifying genes to promote, when the minimum unit of change is probably "how smart people are" or "how social people are", both having many more reasons for being favoured by natural selection.


It’s a messy process, and we may not be able to see where it’s going, but you can bet that there will be changes in human phenotypes and their prominence over the course of many generations.

>Evolution will have hard time identifying genes to promote, when the minimum unit of change is probably "how smart people are" or "how social people are", both having many more reasons for being favoured by natural selection.

If I understand you correctly, that’s just not true. In his seminal work, The Selfish Gene, Richard Dawkins showed that the individual gene is the unit of selection. A genotype that tends to result in a slightly stronger preference for a family life is exactly the kind of thing that could become more prominent, even within one or two generations. I’m sure this is happening right now.

>In your particular example, this arguably derails biological evolution completely - the decision to have kids, and how many kids to have, is dominated by economic and (secondarily) cultural considerations, which change significantly between generations.

I was not making a particular example at all. That is the function of natural selection: it selects for the genotypes had by those who have children who go on to have children themselves.

The selection doesn’t have to happen at the level of a preference for kids. A gene related to diligence or conscientiousness or just about anything else can have effects that ultimately cause differential reproductive success for you and your offspring.

The fact that it’s all too complicated for us to model has bearing on it at all.


10,000 years isn't that short a time in a rapidly changing environment, though it would be in a static one. Human mematic evolution fed into human genetic evolution in a number of ways over that timeframe. As people started getting most of their calories from farming they didn't have as much dietary vitamin D and their skin got lighter. People in Eurasia got more resistant to contagious disease and were able to live together in larger groups, accelerating memetic evolution.

Gould came up with the excellent name "punctuated equilibrium" for the discontinuous nature of genetic change, though the math describing it had existed before he popularized the concept.

It is true, though, that all the big changes of the last 10,000 years seem to have been simple changes in individual genes or their expression rather than more complex changes.


So you're saying that a 6-finger person has a larger change of having children than the person with 5 fingers?

Here's a reality check: 6-finger people also have a much higher probability to be bullied at school and thus never reproduce than the others.


No, that’s not what I’m saying. I’m responding to the assertion that there is no evolution of humans happening at all.

On the timescales evolution operates over, humans being technological creatures in a civilization is essentially a blip. Not relevant whatsoever.

In a few more thousand years, we'll either have transcended biology altogether, be extinct, or be back to the kind of pre-civilization environment where the slow work of evolution matters again.


I think the brain is currently under tremendous evolutionary pressure and is being pushed in a number of directions at once.

Anatomically modern humans have been around for 100-300 thousand years (definitions vary and evidence is scarce and ambiguous). Our bipedal (i.e. hands free to do dexterous things) ancestors go back ~4 million more. If acquiring extra fingers was a net advantage we'd all have them already.


"If acquiring [new trait] was a net advantage, we'd have it already."

If this principle were true in general, it would imply that evolution didn't exist.

Environments change. Competitive landscapes change. Diets change. Parasites/diseases change.

There are genes in humans that are currently undergoing strong selection.

https://www.nature.com/news/massive-genetic-study-shows-how-...


> If this principle were true in general, it would imply that evolution didn't exist.

But it's not true in general, and I gave a specific context: millions of years of human ancestors using their hands to survive in a wide variety of environments and occasionally being born with extra fingers (~0.2% in modern humans, so probably a huge number of opportunities). We have five fingers, so it is unlikely that our six-fingered ancestors had a significant net advantage in general.

I remember reading an article about a present day man with 12 fingers and 12 toes who believes he has an advantage climbing coconut palms. If needs like that had been providing consistent evolutionary pressure on our ancestors, things might be different. Edit: here's a version of it: https://www.cbsnews.com/news/man-with-12-fingers-12-toes-cal...


A bunch of my Wife's cousins all had 6 fingers. They had them removed after birth.


From what I read, fully-functional and fully-formed sixth fingers are exceedingly rare. More often than not they are neither. They just interfere with daily life and attract unwanted attention.


Ever since I was a child I had this strange idea that I was missing fingers (I have 10 like most). From grade school till middle school I even kept counting them as if something was amiss. I mean, it's not like it's actively bothering me or something, but just a bit of a curious quirk: I think I should have 12 fingers. Although in my case it feels like they should be to the side of my pinky, not between the index and thumb. As far as I know my parents didn't have them removed at birth either. Funny enough I believe the gene for it is even dominant (meaning it needs only one copy to express the phenotype), it's just not very common in the general populous.

It would be more useful to have another arm or two.

Is there anyone on HN with 6 fingers? How's your typing? Seems like it could only be a benefit on a keyboard.


Not quite typing, still insightful. A video from the original paper the article refers to: https://static-content.springer.com/esm/art%3A10.1038%2Fs414...


That's a really cool video, is interesting to experience how much my vision tries to reject the extra finger. Is hard to explain exactly, but every time the hand is held in a way that hides fingers, then my brain goes back to predicting it as a standard hand, then pops back to six digits again when all fingers are visible.

Sounds like 5 fingers is the mutation!


Isn't every feature of every living thing the result of a mutation?


Ofcourse. But I wonder wonder if the sixth finger arose in humans or if it's an expression of an previously common structure that has been suppressed for the last couple of million years. I would wager on the latter.


It's an anomaly. Look at the analogous structures in other vertebrates -- in species where digits are discernable (i.e, discounting mammals with hooves or without front limbs at all), there are practically always five. Even a structure as unusual as a bat's wing is made up of five "fingers".


Losing digits seems relatively easy - that's where hooves come from (horses have one toe left, goats two). It's gaining digits that seems very hard. It's possible that some configuration of six fingers could be better, but we probably can't get from our local optimum to that without going through major disadvantages. Apparently five has been the maximum number for most creatures for 420 million years: https://www.reddit.com/r/askscience/comments/1org2e/why_do_m...




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