Why Just Five Digits on Tetrapod Limbs?

Two family members each possessing an extra digit on each limb find that having a sixth finger is beneficial and useful.

A condition called polydactyly has been known ever since the Bible mentioned a case: “And there was again war at Gath, where there was a man of great stature, who had six fingers on each hand, and six toes on each foot, twenty-four in number, and he also was descended from the giants” (II Samuel 21:20). The authors of a study in Nature Communications comment,

Although polydactyly is not rare, and can be traced back at least 1000 years, only its genetics has, until now, been studied. This may in part be due to the belief that supernumerary fingers represent a malformation and are not useful, thus are generally removed at a young age.

Because intact cases are hard to find, few researchers have had a chance to answer questions about extra fingers. Are they functional? Do they have their own muscles and nerves? Are they useful? Are polydactyl people aware of the extra fingers individually? For the first time, a team of 11 researchers evaluated a a 17-year-old polydactyl subject and his 52-year-old mother.

Here, we analyzed the neuromechanics and manipulation abilities of two polydactyly subjects who each possess six fingers on their hands. Anatomical MRI of the supernumerary finger (SF) revealed that it is actuated by extra muscles and nerves, and fMRI identified a distinct cortical representation of the SF. In both subjects, the SF was able to move independently from the other fingers. Polydactyly subjects were able to coordinate the SF with their other fingers for more complex movements than five fingered subjects, and so carry out with only one hand tasks normally requiring two hands. These results demonstrate that a body with significantly more degrees-of-freedom can be controlled by the human nervous system without causing motor deficits or impairments and can instead provide superior manipulation abilities.

In short, an extra finger can be very useful! Think of how many extra tasks you could perform with an extra finger. You could do more tasks with one hand than it usually takes for two. Imagine the faster typing or calculating that could be done! What could a piano player achieve with two extra fingers?

Fig 1 from the paper shows subject P1’s right hand.

The supernumerary finger in the subjects looks just like the other fingers, with knuckles, fingernails and all. It was located between the thumb and index finger, and had a spherical range of motion like the thumb. Its internal anatomy was halfway between a thumb and finger, with the advantages of both:

The extra or supernumerary finger (SF) with three phalanges has a saddle joint similar to that of a normal thumb (Fig. 1e). It has two extrinsic flexor tendons as well as a normal extensor apparatus (Fig. 1c), in addition to dedicated digital nerves. Hence, this polydactyly hand is controlled by more muscles and nerves than normal five-fingered hands. Critically there are intrinsic muscles whose origin is the second metacarpal and whose insertion is to the proximal phalanx of the finger, similar to the muscles of a normal thumb and yielding a spherical range of motion (Fig. 1b, c).

For some reason, the authors didn’t mention toes. Did they fail to look and see if the subjects’ feet had extra digits? That would be odd. Whatever, “The experiments demonstrated that they have no difficulty in controlling the SF in coordination with and independently from the other fingers while no movement deficits of the hand or other limbs were observed.” The subjects were apparently happy to have the extra digits and there was no downside. Who wouldn’t want them? The authors were so surprised and pleased by the results, they feel that robot makers should design robots with six fingers!

Where Has Evolution Been?

Here is a clear case of a beneficial mutation. And yet since the first tetrapod crawled out of the water 400 million Darwin Years ago, evolution seems to have been stuck in a rut: five digits per limb max is all a creature gets. Some animals, like horses and birds, get fewer, but why isn’t polydactyly more common? Why don’t we see evolution producing 7-fingered animals, or 8 or more? Why is polydactyly still considered a genetic “defect” instead of a beneficial trait? (Note: as can be seen in images of polydactyl subjects, not all SF’s are beneficial; some are clearly deformed.)

Evolutionists will invent storytelling words like “canalization” to explain evolutionary conundrums like this. Basically, canalization means that natural selection gets organisms stuck in a rut sometimes, and it’s hard to get out. But then, the opposite is also true! Variation is limitless, such that animals can invent flight, swimming, leaping, crawling and anything else. Evolution can invent wings, tails, eggs, the lack of eggs, pouches, beaks, teeth, gears, meat-eating plants, and eyes (multiple times independently). Any complex organ an animal would find useful can be made special order from Darwin’s Tinkering Shop. So what is the message of evolution— canalization, or innovation?

Notably, the paper does not discuss evolution. This particular mutation for six fingers is not the type of random mutation that evolutionists would need to claim macroevolution, because the genes for fingers, with all their bones, muscles, tendons and parts, are already there. It’s instructive that all four limbs of the Gath Giant had six digits, not just one, two or three. Most likely a regulatory gene or “master switch” failed at some point in development. A switch for digit number failed to turn off before six digits began to develop in the embryo. That would explain why each digit contained the full suite of muscles and bones needed, which would have developed later after the initial digit number was established. Since many mutations are pleiotropic (i.e., affect other genes), the Gath Giant’s mutation may have also altered genetic controls for body size, leading to gigantism. Once again, though, if these mutations had been so beneficial in Darwinian thinking, they should have been selected, and spread throughout the entire human population. Since they did not, Darwinists cannot claim this as evidence for beneficial mutations supporting macroevolution.

What About Creation?

The same question must be asked of creationists. If six fingers are beneficial, why would an intelligent Designer restrict digits to five? The awesome variety in nature shows how easy it would be for the Maker to add or subtract digits. In fact, a Designer could have given each creature any number of fingers and toes suitable for its individual needs. Even whales and dolphins have five digits hidden within their flippers. What is it about five? We switch to Commentary mode for possible answers.

For one thing, no animal is complaining. We humans do marvelously well with our endowments. One cannot say, “If a little is good, more is better” in all cases. Six may work, but seven? Eight? Certainly there will be a point of diminishing returns. Five is a great number that seems to be optimum for most people and animals.

Another answer was suggested by Walter ReMine in his book The Biotic Message (1993). The living world is so designed, he argues, as to send a message: life did not evolve, and there is One Creator. Both creationists and evolutionists agree that organisms are arranged in nested hierarchies: groups with common traits, and groups within groups. The question is whether that arrangement indicates common ancestry or common design. ReMine states the central claim of his argument, which he defends for the next 500 pages:

Life was reasonably designed for survival and for communicating a message that tells where life came from. The biotic message says, “Life is the product of a single designer – life was intentionally designed to resist all other interpretations of origin.” (p. 2o)

Without the complexity, evolutionists might think life just pops into existence easily. Without the unity, theists might tend toward polytheism (i.e., different gods created different types of beings). When we see unity, such as in pentadactyly (5 digits) in the hierarchical group known as tetrapods, it supports the honest seeker with the message that the same Creator made them all.

ReMine appeals to no religious arguments in his book. Message Theory, he argues, is a testable proposition for science, all the more powerful for the many questions it answers that evolutionists fail to answer (as he documents profusely in their own words). The bottom line of “Message Theory” is that creation sends an unambiguous signal of a single Designer.