[engrByDayPianstByNight (OP)]

I'm curious as to the evolutional advantage of human fingers having different lengths. Why is it so? And what would happen if they were all of the same length?

[cheryl j]

They aren't if you make a fist or grasp something.

[~CB]

I did not know this either... Hence, I had to Google it. Below I'm going to state the best answer I found.

"We can look at it from at least four perspectives:
(1) History
(2) Even more history
(3) Function
(4) Plain anatomy


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1. History

If  one wants to consider the evolutionary viewpoint of it, one has to look  at the history of how it came to be instead of just blind speculation.

Notice  how the primates who live on trees and swing from branches generally  have longer fingers and/or longer hands. This allows them to grasp  around particularly thick branches.

I  would like to bring your attention to the gorilla, whose fingers are  more or less the same length (save the thumb). They primarily live on  the ground and natural selection perhaps did not select for the ones  with longer fingers.

 
2. Even more history
But what happened BEFORE that?

Hands first evolved from early water-dwelling creatures. Fingers then followed because they would have better traction with wet soil/ground.

I believe the reason our middle fingers are longest is because of the shape, and its evolutionary lineage. This means that fingered organisms started with already disproportionate finger lengths.

3. Function

We  need to understand what the function of our fingers are. In short, they  are used to perform fine manipulation. This dexterity with our fingers  allows organisms with digits to pick up small things and move them  around.

Longer fingers means longer reach and greater range of manipulation. Too long, though, and it would just be unwieldy.

A quick side note: Our middle finger is longest suggesting its importance for power  grasping. Since that is the axis upon which greatest force will be  subject (it is the middle of the hand), the middle finger has developed  for this function.
The index finger and thumb are used more for precision grasping, due to their close proximity.

Back to the question. Why aren't all the fingers the same length?

1.Too long an index finger will decrease our precision.
2.Too long a thumb will also decrease our precision.

3.A shorter middle finger will decrease our reach; we won't be able to wrap around branches to swing from.
4.The  other fingers have functions that support the previous functions, but  are not the main functional digits. Basically, it helps the other  fingers. If they were longer, it would shift the equilibrium and may  cause the index finger and the middle finger to be less efficient.


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4. Plain anatomy
This section is the last because it holds some more speculation. It's just something which may be worth thinking about, but is not necessarily true. For points with more evidence, please see points 1 and 2 above.


In short: We have a rounded hand bone, and this gives us enough of an advantage that longer fingers are not necessary.


Let's take a look at the bone anatomy of the human hand.

The  small bones of the hand (the part not colored pink, yellow, or blue)  are at the base of your palm. It is the interface between your wrist  joint and the rest of your bones in your palm. As you can see, it is  rounded. As such, this forces our bones to point outwards (almost)  radially.

Now,  having this configuration is more flexible than having a  rectangular/linear configuration like what old robot hands used to look  like.

The  rounded 'cupping' grip that we can achieve thanks to our bone  configuration allows for greater variety of actions to be performed such  as the more fine manipulation of rounded objects.

Here,  having longer fingers doesn't necessarily give an extra advantage. We  have such great degrees of freedom thanks to our finger joints and our
'cupped' configuration, that even longer fingers would just be an artefact.


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All in all, it's not easy to pin down a particular reason. We can just look at the evidence and see where it points to. Speculation can be good, but is best backed up by evidence."

[engrByDayPianstByNight (OP)]

Great explanation. Thanks!

[alancalverd]

Easy answer: the guitar evolved before the piano!

Damn near impossible to play guitar with equal-length fingers. But now after 60 years of guitar and bass, I'm finding it extremely difficult to learn piano - there's always a few milliseconds lead on the left hand (you have to find the note before you pluck it) and the left index finger is too weak to feature much in jazz bass playing (too long - not enough leverage) but turns out to have quite a bit to do on the piano.