Unless you were involved in an unfortunate accident or were born with a rare congenital condition, you probably have five fingers on each hand. But have you ever wondered why we have five fingers? Why not six or four? Let’s break down the evolution of fingers and find out…
Humans have 20 digits — no more, no less. That means five fingers for each hand and five toes for each foot. Finger evolution is similar for other mammals, too. For the most part, they also have five fingers. In fact, no tetrapod has more than five fingers or toes at the end of each limb, as Scientific American explains. Amphibians and reptiles often have fewer, but they, like us, can’t have more. And this evolution of digits really got going about 340 to 360 million years ago.
The Ancient Evolution of Fingers
The evolution of appendages has produced some wild results, and like the crazy arms of the octopus, our fingers began in the water.
Fingers and toes started their evolution in the ancient ocean as fins on our prehistoric aquatic ancestors. Fossil records suggest the earliest fingers even evolved before animals made their way onto land.
From fish to amphibians, the fins began to take on a more finger-like appearance, but evolution didn’t stop her digit design with those prehistoric salamanders. And that’s probably a good thing. Those first amphibians to crawl from the primordial world had really high finger counts – seven or eight or even more. More than we can count on each hand. There was one amphibian, however, who had five fingers at the end of his slippery little limbs. And, by a stroke of luck, he would become the common ancestor of all tetrapods. Ourselves included.
Scientific American says that the great prehistoric digit reduction, from the many aquatic fins to the five fingers that survived epochs to reach us, coincides with the evolution of limbs made for walking on land. And that’s what this all comes down to: evolution.
Throughout time, finger counts have continued to lower for some genetic lines. Experts suggest there’s an evolutionary advantage to having fewer digits, too. For example, birds and dinosaurs who evolved fewer toes ran faster because of it. Additionally, finger evolution is likely to keep lowering finger counts. It won’t, however, ever go up. Not if nature has a say in the matter anyway.
The Genetic Evolution of Our Five-Fingered Hand
Outside of a random mutation, no vertebrate on Earth is capable of growing more than five genetically unique digits per extremity. You can thank finger evolution for that fact.
A set of encoded genes from our amphibian ancestor, passed down through the evolution of fingers, is what set our final finger count. As such, the Hox gene from this long-lost relative and the digital buds on developing embryos work together to stop human hands at five fingers, as Clifford J. Tabin explains in Development, a journal of developmental biology.
The Hox gene tells the embryonic buds to grow into fingers and toes, and thanks to our exponentially-great-grandfather axolotl, developing tetrapod limbs only have five digital buds. This means you couldn’t grow a sixth genetically unique finger even if you tried.
It might seem counterintuitive, but even cases of polydactyly don’t show more than five fingers per hand from a genetic standpoint. The same five digital buds simply produce copies. At the end of the day, they’re basically genetic clones of fingers already coded to exist. It’s like having multiple identical pointer fingers rather than a mysterious and unnamed sixth digit.
Evolution Has The Answers
This is the big question, isn’t it? We know how finger evolution gave humans five fingers, but that doesn’t really explain “why.” The simple answer is evolutionary advantage. The longer answer is “we’re not entirely sure.”
We know that fingers and toes are more advantageous on land than fins. They provide grip for climbing and stability while walking. But we can’t really say why we have five fingers specifically. The evolution of fingers is mysterious in that way. It’s difficult to pinpoint why we ended up with five fingers instead of four or six, but we know that evolution has the answers somewhere.
This is evident in the evolutionary “body plan.” We see the number of fingers cap out at five for all modern animals. We also see the number drop in multiple species. For example, hoofed animals and reptiles. Animals like snakes don’t have any fingers at all. And, nature wouldn’t have evolved hands like these without there being an advantage. We just don’t know exactly what that advantage is yet.
As far as we know, there hasn’t been a single case of evolution giving a vertebrate more digits than its ancestors. In fact, adaptation tends to take digits away, suggesting fewer fingers are better for survival than more.
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The Evolution of Fingers Will Probably Take Even More Away
Animals that have fewer than five fingers seem to have lost their extra digits because they no longer served a purpose. So the most likely explanation – at least the simplest one – is that having the minimum number of digits that your hand and wrist structure can support is a benefit in itself.
There are elevated risks associated with a greater number of appendages dangling in front of predators and toes snagging on debris. Plus, fewer digits are stronger digits since more muscular resources are allocated to them. There may also be other benefits that scientists haven’t researched yet, such as limiting neurological resources spent on running more moving parts.
Regardless of the cause, evolution will likely take us down to four or fewer fingers someday as well. No time in the near future, mind you, but if we survive long enough as a species, it’ll probably happen.
At the end of the day, evidence suggests it was simply a stroke of evolutionary luck that limited us and other tetrapods to five fingers. And it’ll be the evolution of fingers that decides how many digits we end up with as our species progresses. Whatever is most advantageous to our survival.
