3

I’m gonna say per limb the answer is one.

Depends on how you count.
Do you count just the species by themselves, or do you count all the members of a species?
What species do you count? Only animals? What animals do you count?
Do plants count? If they do, what constitutes a limb? What constitutes a digit?
Say you have a tentacle. Is a sucker a digit? Are the tarsal claws at the end of an insect leg?
What about trees? Would trees have millions of digits?

It is impossible to answer.

@ragingloli

In this instance we are thinking of animals that have a dynamic ability to respond to changing stimuli using their limbs.

For instance, your basic earth tree would not count here, since if I go to it with an axe, despite the disparity in our sizes, I will likely fell it, whether or not it would rather I did not. If on the other hand the tree could use one of its branches to pound me into soup, we would want to know on that limb of the tree was there just the one straight lined branch with only small twigs elsewise, or was it a huge limb tipped with articulating sub branches. We’d want to know how many sub branches there were.

In the case of an octupus, there would be eight limbs, and each would count as having one digit. One could argue in this instance the octupus actually is using all its limbs as digits, which would be a vote for 8 digits. Its suckers while functional, are more of a feature on the digit, akin to a fingernail.

Even if we could imagine a species of otherwise normal humans with individual fingertips with retractable prehensile tentacles, only the digit itself would count.

For insects with tarsal claws, those would be more like fingernails, unless they could use them independently. A passive structure like elephant toes, while important, would not really count for more than one independent digit.

Hope you see the gist there.

5
Drawing of elephant hoof

@caravanfan while there are certainly five anatomical digits in its skeleton, and all of them serving an important role in stabilizing the elephant, the elephant would not per se use any of those digits independently.

Digits are used for grasping, stability, paddling, poking, blocking, hitting, cutting, etc.

But, digits that are present, yet surrounded by tissue, like a dolphin fin. Is just a single digited limb despite the underlying bone structure.

@Ltryptophan That’s where we disagree. I still argue that there are 5 digits—they are all just in the fin. If you put a mitten on, you still have 5 digits.

8.

@Ltryptophan What is the most common number of digits in the universe?

Two.

Most of the animals in the universe are insects with two claws on each leg.

https://en.wikipedia.org/wiki/Dactyly

Zero. It is everywhere.

Interesting question. I would hypothesize, that the number wouldn’t matter. Rather. I think that there would need to be, at least, a version of a thumb.

Once you decide that form follows function in biology, it’s pretty clear that it’s pointless to speculate on what can be expected as “average”. It’s bad enough on earth, for example where you might consider anything moving connected to a microbe a digit. You turn that to speculation on the universe at large and it’s pointless. Are toes digits on humans? Clearly this question neglects the arthropods here on earth, the numbers of which bury the higher animals.

Vertebrates usually have 5 “fingers/digits” of some sort, but maybe that is a unique Earth evolution thing. There are a lot of flowers that have 5 petals, too.

But animals usually have bilateral symmetry. And in the universe, there is a lot of H2 floating around, so 2 ought to be the most common number.

I agree with 5.

5 digits is certainly the norm, in regards to vertebrates. However, so are tails.As are two eyes, two ears, etc.
That’s because we all share common ancestors. As we only have knowledge of life on our planet, we can only hypothesize that any other lifeforms, on other planets, would share characteristics that would be similar to each other.
I would think that each planet’s specific environments, would dictate what the characteristics are of the most dominant species there.
Evolution, should be in play, everywhere. It’s possible that some sort of tentacle, could be predominant, or something that we haven’t observed before….