Does anyone know why humans have fingernails?

Are they just a holdover from claws (which would seem to have a legitimate defensive purpose)? Or do our current fingernails serve some other purpose in humans besides being great to scratch an itch? Is there an evolutionary reason for their current shape, position, etc.? Or are they just there?

Obviously, the same question applies to toenails--which I've never used to scratch an itch!

The latest edition of Discover magazine (August 2002) has a short piece on the earliest fossil of a placental mammal (page 10). This 125 million year-old fossil reveals a creature with "curved fingers and sharp claws [that] suggest that [it] was highly skilled at climbing trees." This certainly seems to indicate that our nails, as you have conjectured, are probably holdovers from claws.

Taken from http://ask.yahoo.com/ask/20010504.html

According to the online encyclopedia(BRITANNICA.COM), the human and primate nail corresponds to the claw, hoof, or talon of other animals. Human nails protect the tips of the toes and fingers, while fingernails help us pick up small objects and scratch ourselves.

On the other hand, the feet of primates are capable of gripping objects, just like their hands, so their toenails have much the same function as fingernails. However, human toenails seem to be an evolutionary leftover.

We searched the Web on "toenails fingernails" and "toenail purpose." Both of these searches turned up sites devoted to diseases of the nails, which provided more opinions. On one such site, podiatrist Michael Zapf agrees that nails are essential for manipulation and scratching (and he points out the importance of scratching in a primate or human's life).

But the doctor debunks the notion that nails exist to protect the tips of toes and fingers. He argues that your digits wouldn't be especially sensitive without nails. Dermatologist Mitch Bender appears to agree: "People can get along without nails -- toenails more than fingernails -- but they do make daily life a bit easier."

So, though there's some disagreement about whether or not toenails and fingernails serve to protect our digits, our resources all agree that our nails help us pick up little stuff like pencils, peanuts, and even bottles of nail polish.

Not only are nails great for scrathing itches (which only makes me wonder what the heck an itch IS precisely)...fingernails are great for picking your teeth when you don't have floss or a toothpick available when that irritating chive just won't dislodge itself from that region between tooth and gum...and the tongue tip just won't do the job.

Human nails protect the tips of the toes and fingers, while fingernails help us pick up small objects and scratch ourselves.

Apes use fingernails to delouse each other. I expect our fairly recent ancestors did the same thing, before the invention of soap.

Fingernails have modified quite a bit from early primate claws. They're thinner, broader, flatter. If allowed to grow, they curve slightly from side to side and inward at the tip. There's probably a good reason for that. If they were completely useless, they would have disappeared, because there is a cost to having them: they are vulnerable to breaking and subject to infection (underneath) if we get sharp objects there.
I think they make our hands more flexible in function. They make our fingers like a swiss army knife. Uncut, they are probably useful in getting at food such as grubs, and somewhat useful as weapons. Cut (or chewed off) they can be used as pries, for example in extracting kernels from seeds and nuts. By extracting kernels, we save our teeth somewhat. Some anthropologists thinks that the main reason stone age people had such short lives is that their teeth wore down until useless (gum level) dealing with tough uncooked roots and grains. So any device that allowed removal of the kernel from a seed without damaging teeth would prolong breeding years and thus increase the chances of making it into the gene pool.

I don't know that I buy the holdover notion. Maybe if fingernails are a much more advanced version of claws, but that still leaps an gap of uselessness where claws would have come in very handy for Lucy.

Your fingers are extremely dextrous and have several unique features that improve dexterity. Your fingerprints are gripping pads improved with sweat glands, your thumb and knuckles bend in just right for much finer tool work, and your nails are also tools for finer work (as opposed to thumping rocks like a monkey, gripping a slippery fish like a hawk or climbing trees like a bear).

Fingernails are extremely brittle and don't allow for any kind of industrial strength activity. During hominid evolution, there was no reason for them to develop as they did, since the use of finer tools didn't come until much, much later after the fingernail.