Is it a coincidence that humans ordinarily have five fingers on each hand and five toes on each foot?

Question

Why not five fingers and four toes, for example?

Answer 1

There was a lobe finned fish that evolved into all the terestrial vertebrates (amphibians, reptiles, mammals and birds). Its bone structure included four lobe fins that became the four limbs (thus the name tetrapods) and each had five rays, the bone structure that has become digits. The five fingers / five toes is a result of the creature that moved onto land.

Answer 2

it depends on what you mean by coincidence. Why 5? Why do turtles have 5 toes? I did read once that long ago there were no 5-toed creatures then BLAM suddenly a whole bunch of creatures had them (new creatures, obviously - oops, if you're in Kansas, you should probably NOT be reading this). That was before mammals so all mammals got 5 fingers and toes. But why the same number? Yes, that might just be coincidence. Maybe the question I'd ask is "would the sister/brother of the original creature that have 5 fingers and toes have had an evolutionary advantage if it had, rather, 5 fingers and 4 toes or 3 toes?". I suspect assymetry confers no particular advantage.

Answer 3

Logic would suggest that the number of digits was subject to natural selection at some point. Presumably there'd be a tradeoff between nervous complexity for a larger number of digits, versus increased dexterity. But we can't say if this is really the reason for sure. Besides, that's not what you're asking...

It's unlikely to be a coincidence that we have the same numbers of digits per appendage because appendage development is controlled by a high level set of genes, which would be used for both forelimbs and hindlimbs. That is, the developmental plan for any appendage is implemented using the same genetic controls, inherited from the first ancestor with toes. Like, some genes determine "appendage develops here," and on that appendage other genes determine "digits here and here and here etc" and these genes control development of five digits anywhere the "appendage here" is kicked in.

It's sort of interesting that despite different forelimb and hindlimb function, we have the same number of digits for each - you'd think that evolution could have altered that if there were any advantage. It goes to show that really old, really basic genetic control programs are hard to alter radically - they act very early in development, when small changes are a big deal. If you messed with the genes that specify the way a pattern of five digits forms, you'd probably also mess with a lot of other things controlled by that set of genes, and end up with other things screwed up as well.

And it also goes to show that five probably really is an optimal number for both hands and feet. Evolution got this "right" in the first creatures that had phalanges ... which isn't necessarily a big deal, since they were the ones that survived to be our ancestors.

Answer 4

This depends on what you mean by your question. If you're looking for why we have 5 versus any other number, it has to do with selective pressures, gene frequencies and mate selection. If you're actually that curious, Geoffery Miller has a book called "The Mating Mind." It should set you free. But the short answer is that we have 5 didgits per limb because 1. those of our ancestors with 5 were least likely to get killed before we reproduced and 2. those of us with 5 were best able to find others willing to reproduce with us.
If you're looking for how 5 fingers and 5 toes seem to magically appear from the union of an egg and a sperm, then look up a book by Moore & Persuad called "the developing Human." But again, the short answer is that as embryos our hands and feet are club shaped and we have no fingers/toes. Then the cells inbetween our fingers and toes die and float away, leaving seperate didgits. This cellular death is preprogrammed and has to do with these cell's proximity to a few chemical secreting clusters of cells that direct the body's growth and formation.

Answer 5

Maybe humans used to have four toes, but since our environment calls for 5 fingers and toes, we have adapted. The adaptations are random mutations, but because the organisms with the right adaptations had an advantage, they were the ones who survived and passed on their traits. Because most people have 5 fingers and toes today, it is a very common trait, therefore it is passed on to offspring. Ofcourse, people can lose fingers and toes due to accidents, or mutations in the genes can cause one to born with an abnormal amount of digits. So, no, it's not a coincidence. It's in our DNA to have 5 fingers on a hand and 5 toes on a foot, so we are born with 5 fingers per hand and 5 toes per foot.

Answer 6

I think this has much more to do with our ancestral lineage where five digits are a common trait in most animals with prehensile use of their appendages. Even our closest cousins actively use their feet. Now if you look down at your toes, you will find them to be fairly inconsequential. I sometimes think I should just remove that useless outside digit, but usually that is right after I jamb it really good! We are not a finished or perfected species, we have functionless appendixes, body hair, social dependency, and yes 5 toes. It would seem that we still carry the echos of our ancestors who had hand like dexterity in their feet and aggressive social dependency.

Answer 7

Most of the ancent philosophers would say, devine perportions, in otherwords, five is a universal number (of course they too had five fingers on each hand)

PaleoAnthopoligist would say because austrailipithies(ape like ancestors) had them then we do.

Relgious scolars may say thats thats how god wanted us.

Personaly, i think it just makes life convient so things with less or more fingers got kicked out of the gene pool back before we evovled from apes or whatever.

Answer 8

No, its called creation. The fact that some are born with more or less of these structures is called imperfection.

Answer 9

cuz we were made by god, toes are part of your balence sestem and i guess 5 is better than 4 or 6.

Answer 10

Cos five is my lucky no