An Ode to Fingernails, Humanity’s Loyal Companions
Fingernails hold our secrets in everything from personal data to ancestral roots
Fingernails define humans
Plato once defined man as a “featherless biped,” which prompted Diogenes the Cynic to pluck a chicken and exclaim, “Behold! There is Plato’s man.” In response, Plato refined his definition of man to “a featherless biped with broad flat nails.” Nails, seemingly boring features only useful for scratching and decorating, made Plato’s cut for the definition of human beings.
“Man is a featherless biped with broad flat nails.”
-Plato
Plato’s appreciation of nails is not misplaced. Fingernails are far more interesting than we might think. These keratinous structures that protect our fingertips are important indicators of our identity and health, and they are even a window into our primate origins.
Fingernails reveal our identity (but only for a short period)
Fingernails are the body’s confidantes. Each nail has a unique pattern of contours in the nail plate, the hard surface made of keratin, a tough, fibrous protein that also forms hair. Like fingerprints, our fingernails are unique to us. But unlike fingerprints, our fingernails slowly change as they grow. In 2015, researchers proposed a recognition system that takes advantage of our fingernails’ unique and transient features. Instead of using faces, retinal scans, and fingerprints, which are permanent biometrics, companies could use the distinct patterning of our fingernails as an alternative, transient biometric that could last around 2 months.
Research into transient biometric technology has largely been spurred by a growing interest in the “right to be forgotten,” a principle that protects the privacy of personal and biometric data, especially in a digital context. This principle was implemented in the General Data Protection Regulation (GDPR) of the European Union in 2018, and biometric data regulation has been codified in some states in the United States as well. Fingernails might be the future of biometric technology that protects our privacy.
Fingernails reveal our health
Fingernails reveal more than who we are — they reveal what is going on inside us. Why do some doctors check our fingernails during annual physical exams? Observant and knowledgeable doctors might be checking for nail abnormalities, which are often signs of systemic disease: deep grooves in the nail plate, also known as Beau’s lines, can indicate pulmonary disease, while pigmented bands in nails suggest autoimmune disease. Nail shape, curvature, color, thickness, and attachment are all closely related to the overall health of an individual. Thus, doctors can examine their patient’s fingernails to really nail the diagnosis.
Fingernails are a window to human evolution
Fingernails are more than just confidantes for our health — they are confidantes for our species’ evolution. One of the distinguishing characteristics of primates and humans are our nails. Whereas other mammals, like cats and dogs, have claws, we have flatter, less pointed keratinous structures to protect our fleshy finger pads. Nails and claws have a lot in common, though. In fact, anthropologists and evolutionary biologists contend that primate fingernails evolved from claws.
The transition away from claws to fingernails might have mirrored changes in our ancestors’ habitat, locomotion, diet, and social behavior. As our ancestors adapted to climbing and living in trees, claws might have become cumbersome. Nails might then have evolved as a byproduct of tree-dwelling needs such as grasping hands.
“Fingernails are undoubtedly weaved into the fascinating story of primate evolution, a story we can try to unearth but might never truly nail.”
Nails could also be a byproduct of social groups. Solitary, arboreal mammals like sloths use their long claws to groom themselves, absent any friends to help. Similarly, one of our last common ancestors, a euprimate called Teilhardina brandti, possessed a grooming claw, or toilet claw, for personal grooming. As our ancestors became more social, though, they started to rely more on each other for grooming, a phenomenon called social grooming or allogrooming, which is now mainstream among primates. Claws would be ill suited for plucking bugs from your neighbor’s fur, lest you accidentally scratch them and instigate a brawl.
Teilhardina brandti also has nails, which was a groundbreaking discovery because it showed nails did not merely replace claws. Rather, nails coevolved with claws, replacing claws on some fingers but not others. Moreover, some solitary monkey species have re-evolved grooming claws, so the transition from claws to nails is not necessarily linear. The evolution of nails in primates is not a straightforward path, but then again evolution is never simple.
At some point nails beat claws. Perhaps it was when our ancestors moved into trees and developed flexible fingers for swinging, or perhaps it was when our ancestors migrated out of trees and developed stone tools. Fingernails are undoubtedly weaved into the fascinating story of primate evolution, a story we can try to unearth but might never truly nail.
Fingernail appreciation
From our tree-climbing, fur-grooming ancestors to the tree-cutting, fur-wearing primates we are now, our fingernails have been with us at least part of the journey. Today our fingernails might seem like trite features, but long ago their appearance on the primate stage signaled an important turning point in our evolution. The next time you paint your fingernails or use them to scratch away an itch, take a moment to appreciate them. One day we might rely on fingernail scanning technology to protect our identity, or we might improve our medical diagnoses as our understanding of nail abnormalities expands. We may not know why we have nails, but that shouldn’t stop us from appreciating this small, human-defining feature that nature has fought tooth and nail to bestow upon us.
