# Is there a maximum number of fingers a species can have in each hand? [closed]

We have 5 fingers in each hand (10 fingers in both hands). So we count in a base of 10 (decimal base) which has the accepted digits of 0 to 9. Higher bases have more accepted digits; for example hexadecimal base (base of 16) has 0 to 9 and A to F to represent 0 to 15.

I want to build an alien civilization who have 18 fingers in each hand (36 in both hands). So they have to count in the base of 36. Their language lacks an alphabet yet, so they have learned English alphabet and numerals from humans to use in their countings and possibly speaking: from 0 to 9 and from A to Z (all capital).

I want my civilization to be realistic. So is it possible for an average sized species (just a little bigger than a large adult human) to have 18 fingers in each hand? Is there a maximum number for it?

• Just an amusing tiny fact from history: the ancient Roman system for counting on fingers went to 99 on the five fingers of one hand, to 9,999 on both hands (left hand nothing to 99, right hand hundreds). It was a really nifty trick, which enabled them to show all small numbers of interest unambiguously by showing the hands with the number of sesterces something would cost, for example. And everybody knew and used this system of counting on fingers; we have not only direct literary descriptions, we have statues, paintings and tokens with numbers represented in this way. Sep 10 at 19:04
• Another amusing fact from history: the ancient Babylonians counted in base sixty, a counting system which is still in use for time and angular dimensions. I have it on good authority that the ancient Babylonians did not have sixty fingers. Sep 10 at 19:08
• In fact, the Mayans used base-20, the Babylonians base-60, and the Egyptians used base-12. While we think that we predominantly use base-10 because we have ten fingers, the more technologically advanced ancient cultures used more comprehensive systems. In other words, you're civilization isn't "realistic" because it has enough fingers for your numerical base, they can also be "realistic" because they're smarter than their neighbors.
– JBH
Sep 10 at 23:59
• And there's precedent for no relationship between number base and fingers in SciFi - L. Ron Hubbard's book Battlefield: Earth. The Psychlo antagonists used base-11 math, not because they had 11 fingers, but as a plot point rationalizing why it was so difficult for humans to figure out their mathematics (the Psychols chose to use it to obfuscate their technology). It's good to think about "realistic," but the physiological association is only one reason why your goal may exist.
– JBH
Sep 11 at 0:04
• And lest we forget, while we humans have ten digits (not fingers, we have eight fingers and two thumbs...), the most commonly used number system on the planet today is base-2.
– JBH
Sep 11 at 0:12

I think the biggest limitation is need. Your species needs a reason for 18 fingers on each hand. Something to drive evolution that way.

Your creature's forearms would be the biggest physical hurdle. The human fingers have no muscles in them. The muscles driving things like making a fist are actually found in the forearms, tied to the fingers by a complex web of tendons. The more unique ways you have to control the fingers, the more individual muscles have to exist in the forearms. This means either larger forearms or weaker fingers. We already play games with this balance, which leads to interesting consequences like some fingers not being able to move 100% independently from others.

As an extreme case, consider a species whose entire survival depends on the shepherding of ants. For such a species, it may make sense to have hundreds or thousands of small fingers so that they could put their hand down and interact with hundreds of ants at a time. Those fingers might look more like the legs of a millipede, instead of our fingers.

– BMF
Sep 10 at 20:52

The maximum number of fingers your species may have is a tradeoff between the need for strength and the need for dexterity.

A creature with only two fingers on one hand may be able to apply a great deal of force between them. As the number of fingers increases, the maximum amount of force per finger decreases, while the ability to perform fine manipulation increases.

The benefits of having more than five or six fingers per hand would likely not be particularly greater than that of having five or six fingers, and would come at the cost of greater nervous complexity and a reduced ability to apply raw strength rather than perform fine manipulation.

So rather than simply counting the fingers on two hands, perhaps count something else, like the individual finger bones or the joints on the two hands. Counting your fingers doesn't have to be the only way.

## It's fine for an alien

Several tetrapod ancestors had seven or eight digits per limb, Acanthostega had 8 fingers per limb. Creatures evolving from fish tetrapods had lots of fingers adapted from the original fin rays.

Tetrapods settled on five as a compromise to make walking easier by making the toes thicker and thus stronger. You see a slow loss of toes in early terrestrial tetrapods.

Loss of digits has happened many times, but adding more is evolutionarily difficult, although your species could have just not lost as many in the first place.

Everything today with five toes inherited that pattern from the same ancestor. There is no reason an alien could not have have inherited a different pattern. Although it may be more realistic to give them 6 limbs with nine digits each to get the number you want.

There is no limit to number of fingers. We just happen to have 10 digits on our hands.

There is also no hard and fast rule to use the number of fingers as a base for your maths.

Ancient mathematical systems used base 60, base 12, base 20 and probably others. Yet all ancients had ten fingers like us.

• @SnackExchange because we all evolved from the same fish which had 10. But there were other fish who had 8 per limb Sep 10 at 21:38
• Even modern cultures often use different bases. Currently living people in various places on Earth use base 4, base 5, and even base 27 numeral systems. Sep 10 at 22:37
• @LoganR.Kearsley's observation is important! "There are also base-27 systems, developed by cultures that use the whole human body to keep track of numbers, and this system is used in Telefol and other Central New Guinea languages. Instead of having separate words for each number, they actually use the names of the 27 body parts they reference!" In other words, this can affect the OP's not-yet-developed language.
– JBH
Sep 11 at 0:06
• However, I need to take issue with the phrase, "there is no limit to [the] number of fingers." Fingers develop for survival reasons long (long...) before the need to count. If we assume the primary reason for fingers is to grip something, then we can assume that the ability to touch the tip of your fingers with your thumb (a rough conclusion, certainly) is a basic requirement, and therefore there are only so many fingers one can have before it's no longer possible to touch those finger tips or (by extension) perfect a grip. At that point, they become a liability.
– JBH
Sep 11 at 0:10
• @JBH opposable digits first evolved long after fingers, and most tetrapods still don't have them, so I think we can safely exclude grip or opposability as a driving force in finger evolution. Sep 12 at 1:40

# It will be determined by your species DNA and nothing else

Terrestrial species have a rather stubborn tendency to keep the pentadactyl configuration, which spans all mammals, reptiles, birds, and amphibians. The 5-digit configuration is hard-coded into the homeobox region of our DNA, where the basic body plan is coded. The reason every higher animal born for so many millions of years have been unable to shake this design is because the homeobox region of our DNA is fervently protected by many redundant DNA repair mechanisms. What this means is, that while we see polydactyl cats with "double paws" all the time, and likewise for rabbits; when those cats and rabbits have babies, the mutated code for extra digits will be corrected back to the pentadactyl configuration during several phases of the embryo's development. These mechanisms are not completely foolproof, but in the end, the species shall have the body plan it began with.

## Natural forcings are not enough.

Hollywood and pulp fiction like to imagine DNA as a surrogate for God and allow it to do any arbitrary modification "if the environment provides enough pressure." That makes for cool movie monsters and sells a lot of tickets, but it just doesn't work like that. Consider the arctic hare, which spends much of its life running from foxes and eagles over powdery snow. It has done this chase for many millions of years, and very often, double-pawed kits are born with natural snowshoes. A hare with wider paws is naturally more proficient running over the snow. But with billions of kits born with polydactyly, and outrunning their siblings over the eons, all hares are still coded for five digits: five on the front paw, and only four emergent on the rear.

Does the fact that hares have 18 toes mean the homeobox has changed? It does not. It is possible to "switch off" the expression of a body feature, but the DNA still retains the basic plan for five digits. Similarly, you may have heard about "Talpid," the mutant chicken which had crocodile teeth, apparently because the code for teeth has never been erased from the chicken. The assumption is that it had just been "switched off." Likewise, the missing vestigial toes on a rodent can and have returned from their ancestors. For example, it is believed that all members of the species of the family of Caviidae, including the guinea pig, have lost one digit (digit I) in the front feet and two digits (I and V) in the hind feet over time. They believe this because the toes can and have returned through atavistic polydactyly. Digit V returns with the prolongation of metatarsal V; digit I has no existing metatarsal and can manifest as an entirely new digit. It is reasonable to assume the lost hind toe can be switched on and 20-toed rabbits could exist. But while atavistic polydactyly has been shown to make "strains" of dependents with heritable reverted features, other forms of polydactyly producing additional digits beyond what is planned have not been found to successfully replicate. This is because such mutations are not simple "switches" within the DNA code, but errors in it that get filtered out in the offspring.

## It can work as an alien species

Since you are building an alien civilization, then as long as it does not relate back to terrestrial DNA you can have it coded for whatever body plan that you like. The fact that 18 fingers might be cumbersome or odd-looking won't prevent the species from evolving if that's the "plan" coded into their DNA; the DNA is actually stronger than the environment in this regard. Environmental forcings are primarily limited in their influence to switching code on or off, it's not suggested that the environment can write new genetic code. Nearly all new code is known to be harmful of fatal to the species, so if an organism responded to pressures with actual DNA modifications they more often than not would be jumping out of the pot and into the proverbial fire.

This is not to say that your imagined body plan is actually possible; but rather that it is impossible to disprove, and so it can be believable. A terrestrial species with 18 digits would not pass the plausible deniability test however; we simply understand too much about DNA repair mechanisms which prevent such arbitrary changes.

• One of the few examples where natural selection fails. Sep 11 at 23:49

Frame challenge regarding the number system:

It is possible that base-36 is prohibitively impractical in use. They would rather resort to base-6.

The problem with base-36 (and all base-n, where n is large) is that it is hard to learn and use reliably. To be able to do addition, you need to learn all combinations of n + m, where m and n are any of the digits. m = 0 is trivial, and m = 1 comes from learning the sequence so that is easy learn as well.

In base-10, there is surprisingly little to learn compared to base-36. You need to learn in what order the 10 digits are (piece of cake, preschoolers can learn it), and then 2 + 2, 2 + 3, 2 + 4, ... 2 + 9, 3 + 2, 3 + 3, 3 + 4, ... 3 + 9, ..., ..., 9 + 2, 9 + 3, ..., 9 + 9. That makes 8 * 8 sums that you need to be able to come up without thinking, correctly, otherwise you are clumsy and error-prone.

Half of it can be ditched, though, because m + n = n + m, so in order to be able to basic additions fluidly, you need to learn 32 (8 * 8 / 2) "primordial additions" that all additions are based on, and you need to learn them absolutely correctly. You cannot make such mistake that 3 + 6 = 8.

In base-36, it becomes much less manageable: 2 + 2, 2 + 3, ..., 2 + 33, 2 + 35, ..., ..., 35 + 35. After ditching half of this, we still have 578 (34 * 34 / 2) distinct nontrivial additions between mere two single digits, and you need to learn all of those, otherwise you are pretty much screwed when doing anything with bigger than single digit numbers. You cannot make such mistake that D + J = X. It is W.

That makes base-36 very impractical if you cannot write your numbers. If you have to adopt them form another culture, then you have been in serious trouble with your base-36 until you got the numbers.

The aliens would be better off with base-6. This has many advantages: there is now only 8 (4 * 4 / 2) single-digit additions that need to be learned, and then you can do addition. There is little to memorize, and it is easy to transmit also orally without any written numbers.

In addition, if your aliens do have 36 fingers, they can use them easily in groups of six, giving them ability to display 6 distinct numbers just with the 36 fingers, ie. it goes up to ZZZZZZ (if you borrow the English alphabet). That is, they can go up to 2176782335 (instead of 36) using this system that is also easier to learn and less error prone.

If they had two subgroups, one using base-36 and other base-6, the base-6 group would have a significant advantage over the other, and base-36 would be dropped eventually in favor of base-6.