Fingernails serve several important functions that were crucial for our ancestors and remain useful today. Given that our sense of touch mostly happens through our fingers, its only logical that they are very sensitive and have lots of nerve endings. Nails shield the sensitive fingertips and the underlying bone from injury and trauma. The nail bed underneath is rich in nerve endings and blood vessels, and nails act as a protective plate. Nails provide crucial support for manipulating small objects. They act as a counter-pressure surface when you pick things up, allowing for precise pinching and gripping. Try picking up a coin without using your nails…it’s much harder. Nails allow us to scratch itches and remove parasites or debris from skin (and even the occasional splinter obtained through reckless gardening). This was likely more important for our ancestors but remains a daily function. Nails help with tasks like peeling, prying, and scraping. They’re essentially built-in tools for manipulating our environment. Nails also enhance tactile sensation indirectly. The nail itself isn’t sensitive, but it provides a firm backing that allows the fingertip to better sense pressure and texture when touching objects. Our stone-age ancestors likely used nails for grooming (both self and social), foraging (digging, peeling bark, opening fruits), and potentially for defense or fighting (not sure I would want to challenge a saber-toothed tiger with my fingernails, but you never know). Unlike claws, which are curved and pointed for gripping or attacking, our flatter nails evolved to support our opposable thumbs and precision grip—one of humanity’s defining features. While we don’t rely on nails for survival like our ancestors did, they remain functionally important for everyday tasks—typing, buttoning clothes, using touchscreens, and countless other fine motor activities we take for granted. Just bandage one of your forefinger nails and see how aware you become of the importance of your fingernails.
Fingernail thickness varies quite a bit between individuals due to several factors. Heredity is the primary determinant and nail thickness. Growth rate, and overall structure are largely inherited traits. If your parents have thick nails, you’re more likely to have them too. Nutritional deficiencies can thin nails due to lack of biotin (vitamin B7). A deficiency of iron, protein, or zinc can also lead to thin, brittle nails. Even inadequate calcium can also play a role. Hypothyroidism often causes thick nails as does Psoriasis and fungal infections. Meanwhile, Anemia and malnutrition typically thin them. Nails tend to thicken with age, more so toenails than fingernails. This happens because nail growth slows down and the nail plate can accumulate more layers. However, some people experience thinning nails as they age due to decreased circulation or nutritional absorption. Swimmers sometimes get thin nails as repeated water exposure can weaken and thin nails. Harsh detergents and nail polish remover (not to mention household chemicals like acetone) can damage the nail plate. Trauma or injury to the nail matrix (the growing part) can permanently alter or deform nail thickness. Attacking an ingrown nail can feel never-ending, but if you attack too hard you risk permanently altering your nail profile (my left big toe stands as an example of this). Just like some people have thick versus thin hair, there’s simply natural variation in nail thickness among healthy individuals. The normal range is quite broad—typically 0.5-0.75 mm thick, but healthy nails can fall outside this range.
There’s no evidence that nail thickness reflects meaningful evolutionary distinctions between human populations or individuals. Unlike traits that faced strong evolutionary pressure (like skin color adapting to UV exposure, or body proportions adapting to climate), nail thickness doesn’t appear to have provided significant survival or reproductive advantages that would drive evolutionary divergence. There aren’t consistent differences in nail thickness between different geographic populations or ethnic groups that would suggest adaptive evolution. The variation is mostly individual and familial rather than population-based. Modern human nails evolved relatively early in primate evolution. By the time Homo Sapiens emerged, our nail structure was already established and has remained fairly uniform across all human populations. Rather than evolutionary distinctions, nail thickness primarily indicates individual genetic variation (like height or hair texture), current health and nutritional status, age-related changes, and some amount of environmental exposure. The thickness variation we see within modern humans appears to be a neutral variation that doesn’t indicate any adaptive differences or evolutionary branching. It’s similar to earlobe attachment or widow’s peaks: genetic traits that vary between people but don’t reflect evolutionary adaptations or meaningful biological distinctions.
I am exploring the humble fingernail for two reasons…first, they are simply an interesting aspect of the human landscape, and secondly, I spend a lot of time contemplating them while I am chewing on them. Nail biting (onychophagia) is indeed very common. Estimates suggest that 20-30% of children and 5-10% of adults do it regularly. It’s so prevalent mostly due to psychological factors like stress and anxiety relief. Nail biting often functions as a self-soothing behavior (a graduation from thumb-sucking I imagine). The repetitive action can be calming during moments of tension, boredom, or nervousness. It’s a form of “nervous habit” or body-focused repetitive behavior. Interestingly, some research links nail biting to perfectionism. People may start biting to “fix” a rough edge or hangnail, then continue compulsively. Of course, this form of perfectionism leads to very imperfectly looking fingertips. And then there’s the issue of emotional regulation. For many people, nail biting becomes an unconscious way to manage uncomfortable emotions or redirect restless energy. There are also developmental factors at play. Most nail biters start young (often around age 3-4), and it can become deeply ingrained. Many children bite nails during transitions or stressful periods and either outgrow it or carry it into adulthood.
When I think about my upbringing, I was constantly on the move. My mother even flew from Venezuela to Florida just to give birth to me. That means I had one Pan Am Clipper ride in utero followed by another back down into the tropics as an infant. Both ways we stopped in Havana, which was in the pre-Castro days of Lucky Luciano’s control of that gambling Mecca. Four years of being raised by a German governess living in a Spanish-speaking country and having to learn both English and Spanish (presumably with a German accent) must have had some stressful moments. My mother used to tell me that I was very polite and well-trained as a young child, but perhaps I was just scared out of my mind and unsure what language to speak to whom. That was followed by a boat ride to New Orleans and moving to Santa Monica where I attended nursery school with Jerry Lewis’ kids (totally true) only to get whisked back to the tropics of Costa Rica the following year by way of snowy Ithaca, where the neighbor kid, Eddie, had his way with me in the hayloft of the barn until he got discovered. If that won’t make a kid start biting his nails, what will?
Some researchers link nail biting to oral-stage behaviors. The mouth provides comfort, similar to thumb-sucking in younger children. Why it persists after that is usually linked to the need for immediate gratification. There’s instant sensory feedback and temporary relief, which reinforces the behavior. I know myself well enough to recognize that instant gratification is a fairly big theme in my life, so that hangs together. Last time I looked, my fingers are always with me, making it an easy habit to fall into anywhere, anytime. My nail biting is often unconscious (or is that subconscious?). Many people bite their nails without realizing it, making it hard to stop. I know I catch myself in the act all the time. While I can occasionally worry about the look of my nails, not being a hand model like George Costanza of Seinfeld, there is a low social consequence attached to nail biting. Unlike some other nervous habits, nail biting is fairly socially acceptable, so there’s less external pressure to quit. Kim does glare at me if she hears me biting my nails, but that’s only while we are quietly watching TV or something.
Nail biting often becomes self-perpetuating. Stress triggers biting → damaged nails feel rough → trying to “smooth” them by biting more → cycle continues. I’ve tried getting manicures and putting bitter clear polish on my nails, but nothing has worked for long. Most nail biters want to stop but find it challenging because it’s both a physical habit and an emotional coping mechanism. But all the books say that nail biting can definitely be stopped in adults, though it often requires sustained effort since the habit is typically well-established. What tends to work are the behavior modification approaches that work so well for weight loss (NOT!). Habit reversal training is considered the gold standard in this curative. Its all about stimulus control, mindfulness and awareness…none of which is easy for us OCD types. I suppose you can try to address the underlying causes through stress management and therapy, But that’s a lot of effort for something as tangential to life as a few scraggly nail beds. Maybe I’ll just wait until Trump discovers my blog…then I just get them pulled out for me at Guantanamo…back to the tropics for me.