Why Humans Donít Have Claws
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In 2008 Christopher Hitchens, author of "God Is Not Great" went on a book-promoting debate tour with Pastor Douglas Wilson of Christ Church in Moscow, Idaho and a senior fellow at New Saint Andrews College. Hitchens states that Pastor Wilson often introduces his part of the debate with statements that include, "God knew that we were going to need to pick up dimes, and so He gave us fingernails." That statement doesnít even qualify as a Just So Story; scientifically it gives us pure, utter nonsense. Moreover, it indicates how the sublime doctrine emanating from the history-shaking, civilization-shaping dialogue between Greek logic and Hebrew prophecy has degenerated into the outright silliness of a clown religion when the modern world has presented it with an existential challenge.
So how did humans get fingernails? More specifically, given that humans evolved from a lower class of mammals, which have claws, how did those claws evolve into fingernails? What mutations got promoted by natural selection and why?
We can start to answer those questions by noting that creatures that inhabit the trees, especially those that jump from branch to branch, suffer from the existence of claws. If a claw catches on the treeís bark, the creature may fall from the tree. If the creature is small enough, it will survive the fall relatively unharmed. Larger creatures, though, will suffer serious injury.
Why donít squirrels (Class - Mammalia, Order - Rodentia, Family - Sciuridae) have retractable claws? Their fingers are too long; thereís no good place into which the claws can retract. So why donít squirrels have nails? They are small and light and, therefore, less likely to break a bone or suffer grave injury if they fall from a tree, so thereís no selective pressure to promote the necessary mutations. Further, squirrels have very loose skin that, in a fall, can spread out to form a shallow parachute. Think of flying (actually gliding) squirrels and how they evolved.
For larger creatures we have two possible solutions of the problem of falling from trees: retractable claws (in cats) or claws flattened into easily breakable nails (in primates).
The evolution of claws into finger- and toenails occurred early in the evolution of Order Primates (which order includes primarily lemurs, tarsiers, lorises, monkeys, and apes): indeed, biologists take possession of nails instead of claws as one of the defining characteristics of the order (even though not all species of primates carry the trait). The change appears to have evolved as a result of the oldest primatesí practice of using their gripping hands and feet, with their long, inward-closing fingers, to hang from branches as they swung through the trees of their native forests.
Fifty-eight to fifty-five million years ago (late in the Paleocene Epoch), in the vast subtropical forests that covered what we now call western North Dakota, a strange, squirrel-like creature climbed the trees. In a climate similar to that of Southern Florida today the 2-1/2 foot long Plesiadapis looked a bit like a lemur, but one with claws rather than nails on its toes and fingers and with eyes that looked sideways rather than straight ahead. This far ancestor of the primates actually looked more like a rodent, with a long snout holding jaws filled with rodent-like teeth, including long, gnawing incisors that a gap kept separate from the molars. An observer might reasonably mistake the creature for a giant squirrel with elongated limbs.
By 47 Myr ago, in the middle of the Eocene Epoch (essentially 56 to 34 Myr ago), these creatures had nails where claws had grown in their ancestors. In May 2009 paleontologists reported the discovery of a 95-percent complete skeleton of a female Darwinius masillae (suborder Euprimates, superfamily Adapoidea, family Notharctidae, subfamily Cercamoniinae) entombed in a bed of volcanic ash in Messel, Germany. Originally unearthed in 1983, this most complete fossil primate found so far, which primate lived in a mid-Eocene rain forest, had nails and opposable thumbs. Of course, we donít know whether Darwinius evolved directly from Plesiadapis or from a related creature, but the resemblances between the examples we have of the two genera testify to parallel evolution at the least.
The nails themselves didnít survive the burial, but the finger bones did. The way a claw attaches to the last phalanx on each finger and toe differs from the way a nail attaches and that difference will show as a difference in the shape of the bone; to wit, the bone with have a scutiform shape, the broad shape of a shield. The researchers found that the terminal phalanges of the hands and the feet of Darwinius masillae were scutiform (shield-shaped) and, therefore, nail-bearing.
So how does a squirrel-like creature evolve into a lemur-like creature and thence into an ape? What facts do we need to bring into play to develop a plausible scenario of that evolution? Five considerations come to mind.
1. Animals of a given species have claws of varying width and thickness. Animals with wider claws are less likely to get those claws caught in the gaps that exist in the bark of some trees. Natural selection works on that kind of difference (because falling out of a tree is not good for an animalís reproductive success) and promotes the mutations that give some animals a reproductive advantage over others of their kind. Thus, tree climbers with wider claws would come to predominate in their population.
2. The ability to grip a branch, however imperfectly, gives the creature better balance as it walks on branches, especially narrow ones. The further the animal can go, the more food it gets and the less predation it suffers. Those benefits promote the mutations that make them available. In particular, they promote mutations that lengthen the phalanges (finger bones), slowly turning paw pads into fingers. Thus, all primates have hands instead of paws and those hands have nails instead of claws.
3. A better grip enables the creature to be bigger than its ancestors. Because of that grip the animal is less likely to fall out of a tree, so it reproduces a little more prolifically (as an average over a large set of the animals). But at the same time, the animalís growing bigger makes the hands bigger, which improves the grip even more. Eventually the primate can grip branches well enough to brachiate; that is, swing from branch to branch. Instead of climbing down one tree in order to climb up another, the primate can simply leap from one tree to the other.
4. A brachiating style promotes the changes in the shoulders that enable primates to move their arms freely and that provide the basis for the human ability to throw things. The ability to stretch our arms forward and then swing them to the side is one feature that differentiates us from other animals. The brachiating style also contributes to the evolution of claws into nails. An animal that goes to leap from one tree to another, swinging from one branch to another, will not likely survive if a claw gets caught in the branch itís trying to leave behind: the creature will be thrown off course and will likely fall to the ground. If that animal has easily breakable nails, it will not be thrown widely off course and will likely survive the snag. With regard to the ability to brachiate safely, those who did it best reproduced themselves best and thereby promoted the mutations that encoded the features that gave them that ability.
5. Primate fingers have sensitive tactile pads, which are also related to improved grip through the wrinkle-like patterns that form our fingerprints. The finer sense of touch enhances the ability to grip branches accurately. This is another consequence of the evolution of claws into nails. As claws evolved into nails, the last phalanx in each finger widened to support the nail. That widening also widened the fingerpads, improving their sensitivity and their grip. Thus we have the modern primate hand.
In that way animals of Order Primates evolved with finger- and toenails in place of claws. In addition, the toes and fingers became longer and the inboard fingers and toes shifted away from the other fingers, becoming thumbs (pollex; pl - pollices) and big toes (hallux; pl - halluces), thereby enabling the hands and feet to grasp objects, such as branches without getting caught in the bark.
Letís end this essay with a return to the pseudo-theological proposition with which I began it: God gave humans fingernails so that they could pick up dimes. If we accept that proposition as true to Reality, then we must certainly ask why God also gave fingernails to lemurs, monkeys, and apes, which have no such need. Of course, we will not get a proper answer to that question or, worse, we will get a response to the effect that we cannot understand Godís intentions, except where they pertain to Humanity.
The descent into cuteness and utter silliness masks an egocentrism emanating from the corruption of Christianity. The very idea that The Thing That Created Reality cares about my ability to pick up dimes flies in the face of the traditional interpretation of the faith, the kind of interpretation that we see in Martin Lutherís famous Ninety-Five Theses. Jesus did not say, "Blessed are those who kiss the mirror, for God will grant them trivial favors." No, the traditional interpretation tells us that any encounter with God must evoke sheer terror, which we can only meet with the kind of humility that acknowledges our utter unimportance in the grand scheme of the Universe. But that attitude does not put butts in pews on Sunday and certainly does not fill the collection plate. And that fact, and its attendant need to appeal to the egotistical self-obsessions of the parishioners, has led to a slow degradation of Christian doctrine.
To look at Christianity today must give any truly devout person the same feeling as would seeing the Hebrew prophets and Greek philosophers, Moses and Aristotle, Isaiah and Socrates, Jeremiah and Plato, transformed, costumed, and painted into hideously deformed clowns. Far better, we should think, that Christianity vanish from this world altogether than to suffer such a heinously degraded fate. Perhaps, to be perfectly facetious, we can hypothesize that God gave humans fingernails to scrape on blackboards, creating a noise that makes an appropriate commentary on the kind of theology that we see today.
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