In general, it seems that every human trait can also be found somewhere in the animal world. Language, learning, emotions, society, altruism, tool making, etc. can all be identified in one animal or another. The difference for humans may just be in the extent/complexity of our abilities…yes, I read Carl Sagan’s book “Shadows of Forgotten Ancestors”. 
Perhaps some of our specific behaviors are unique (e.g., the only creature to have religion…or to build an airplane), but our basic characteristics are not so unique. Of course, this is not so surprising considering our evolutionary connections. Anyway, I thought I’d pose this question to the forum…can you think of any uniquely “human” characteristics?
Hmmm… a toughie. Most of my immediate answers are undone by counter-examples I think of:
War: I believe different tribes of chimps will wage war against each other.
Murder: That is, individual murder, not warfare. Female praying mantises often eat their mates.
Debatable:
Deliberate self-destructive behavior: Either animals are trying to do something else that gets them killed (crossing a highway), they’re sick, or they’re cast in a Disney snuff film (lemmings).
Best candidates:
Organized religion: Who knows whether dogs believe in a higher power? But if they do, they don’t gather every 7 days to worship it.
Distinct languages: Whales (of the same species) born and raised on completely different sides of the Earth probably can understand, or at least understand the emotion behind, each others songs. But a human that speaks only Mandarin Chinese can’t communicate at all with a human that speaks only American English. (If they’re face-to-face, they might start picking up on body language; if not [solely vocal], there’s no hope.)
Xenophobia/bigotry: Animals may fear and/or fight strangers, but only because they don’t know them. I’m talking about things such as ethnic supremacy, lifestyle phobias (homophobia and the like), or snobbery.
Nuclear technology: Some birds use sticks to get at insects in holes (physical tech), bees use special chemistry to convert nectars into honey (chemical). But actual transmutation of elements or the use of natural transmutation of elements (uranium to plutonium, hydrogen to helium, carbon-14 dating, technetium production) is something only humans do.
Space/Hostile Environment Travel: Sure, animals can exist for a short time out of their environment. But to spend a week going to the Moon, or to orbit the Earth for a year. That’s something only a human can do.
Any more examples will just be getting more and more technically based, which is not where I think you were going.
Only ones that go to work, cook foods, have the need to ask questions like this, etc. Anything that has to do with thinking abstractly and self-awareness is usually only found in the human domain. Organized religion is about as relevant as organized labor unions, just a function of human thinking.
On the “organised religion” front, did anyone see the documentary “Wolves of the Sea” about the behaviour of various pods of killer whales?
A particular pod hunted baby seals in a spectacular fashion: they stationed themselves off a breeding ground and deliberately beached themselves between waves, enabling them to pick off the popplers and catch the next wave back into the depths. All merely very impressive so far.
What freaked me out was this: as the pod is about to depart the breeding grounds for the year, the whales catch one final baby seal. They take it out 100 metres off shore and play with it a while. Then they deposit it unharmed back on the beach.
I’ll be laying off the whale sashimi a while yet: their clown might eat me.
picmr
As far as I know, humans are the only creatures that kill simply for the pleasure of it. All other animals kill for food or if they are threatened in some way. If you walk up on a grizzly, it’ll probably kill you, but it’s not activly hunting you, just for the thrill of killing you…
I saw the same show picmr did, about the killer whales bringing the seal pup back unharmed. This shows clearly that they do not kill just for fun. Only for food or protection.
We, on the other hand, load up our campers with beer and bullets, just to watch a buck drop, so we can hang it’s head on our wall
Humans are also one of only a VERY few animals that have sex for fun. 
Let’s just narrow the question down to the primates, I think there are about 100-125 of us. A little Nair in the right places and a little American Sign Language? Well, a LOT of Nair.
The single thing that seems reasonable and separate to me is our adaptability. We change hair, body paint, tools, foods, clothing, mating forms, child rearing practices, body piercing, educational forms, name anything and it is done differently somewhere else on the planet.
religion - perhaps this is one unique quality (or do moths worship the flame? :))
killing for pleasure - ever see a domesticated cat (one that does not need to hunt for food) toy with a mouse or a bird? (p.s. - this would be an awful way to define being human!)
distinct languages - I wonder if whale/dolphin pods or if tribes of chimps develop dialects (variations) on their basic instinctual language.
xenophobia/etc. - I think this may be why tribes of chimps go to war with each other
nuke tech - as you said, this may relate to the “extent/complexity” bit I mentioned…i.e., human tech is more advanced than chimp tech
other environments - ditto - we can’t really do that without our high-tech stuff - also, some creatures (e.g., giardia) can encyst themselves until they are back in their element.
going to work - ants/bees, etc. work outside their home…lions hunt etc.
asking questions like this - good one
abstract thinking/self-awareness - the “higher” apes can do this (again, to a lesser extent)
cook foods - good one - perhaps we could add “taming fire”, but this may just be another more advanced tech
Anyway, I’m not shooting down ideas…it’s all debateable. Parse it down enough, and simliarities can probably be found somewhere else. So, perhaps we are best defined by the sum of our abilities/biology and how our behavior exploits them.
suicide – only humans can deliberately kill themselves.
monogamy – humans are the only species that practice this.
sex – only humans can have sex with absolutely no reproductive intent, but rather, for pleasure.
There are other animals that practice monogamy - Geese, Canada Geese, there must be more but I can’t think of them now…
Bonobos behave rather like humans in the sex without reproductive intent. Well, very like humans.
The trainer of the dolphin in the original Flipper shows, claims that the dolphin commited suicide by holding his breath… something us humans can NOT do.
Dolphins are also known to have sex just for fun. There are very few animals that do this, but we are not exclusive in doing so.
Wasn’t it Mark Twain that said humans are the only animals that blush, or need to.
Quote from Ozone:
Dolphins are also known to have sex just for fun. There are very few animals that do this, but we are not exclusive in doing so.
Ummm… does ejaculation occur? If so, is it still while in the female?
I’m not so sure. Isaac Asimov wrote a short story called “Pâté de Foie Gras” where he describes a goose that uses oxygen (isotope 18) to convert iron (isotope 56) to gold (isotope 197). The goose “excretes” the gold when it produces eggs, i.e. it lays golden eggs. Never underestimate the animal kingdom, my friend! 
Of course, this goose was unable to reproduce, since the golden eggs wouldn’t hatch, so this was an evolutionary dead end.
(N.B. to deflect any accusations of prevarication, I fell obligated to add that obviously Isaac Asimov’s story is fictional.)
Humans are the only species of animal that lives in my house and do not freak out when there’s a thunderstoem outside.
First, about Monogomy: Mandarin Ducks also practice this, so its not just humans. I think other birds do to, and
probably other animals as well.
Humans are animals, we are exactly like them in every way, and our advances in science and technology are a testament to the fact that we are similar.
Take, for example, a deer. A male deer has large protruding horns, very sharp, for protection, along with powerful leg muscles for fast running and bounding through the forest to escape from predators, and hard hooves to protect his feet from the brambles and thorns and sundry other obstacles on the forest floor. He’d be a tough match for any predator. And how did he become that way? Evolution. It took sometime for mr. deer to become as adapted as he has.
Enter, the human. A long pink tube, completely of soft flesh, and little hair, who can’t survive a night without catching a cold. Why don’t we have hooves? Why didn’t god give us some evolutionary advantage to compete with deer? He did: the human mind. Instead of hooves or horns, we got our brains, which allowed our ancestors spears, very sharp, for protection, and later, automobiles for fast driving, and comfortable shoes to protect our feet. Why don’t humans evolve like bunnies when its cold and grow a large coat of hair? We build a furnace. 'Nuff said.
Our society, religion, technology are the result of our evolutionary advantage which all animals have to varying degrees. We just got a better one =) Cool, huh?
Vandal: “Ummm… does ejaculation occur? If so, is it still while in the female?”
Sure, but since the egg is not ready for fertilization nothing happens.
You wouldn’t say this if you would have ever seen the carnage caused by a 'coon in the chicken house. A ‘coon will kill for the shear fun of killin’.
michael
Most of the traditional answers to this question involve the use of tools. At one time, it was said that humans were the only animal to use tools. This doesn’t work, because otters and some birds (among others) use stones to crack open shells. OK, said the philosophers, but Man is still the only animal that makes tools. Then some chimpanzees were observed to chip flint to produce a sharp edge, state-of-the-art technology for most of human history. I propose that the answer is that humans are the only animal that depends on tools. An otter or bird or chimp can get along just fine without their rocks or sticks… A person cannot. If a person finds it necessary to perform some task, and does not have the appropriate tools, the person will either improvise with the tools they do have, make tools, or obtain them from elsewhere.
And by the way, all animals have sex for fun. The reason it’s fun is to ensure the survival of the species, but do you really think that two dogs humping are thinking about puppies? Some animals are even observed to masturbate.
Bonobos monkeys have been observed to masturbate. If that’s not sex just for fun, tell me what is. Unless they’ve got a good pitching arm, there’s no chance at reproduction.
(They also engage in sex for no reproductive purpose). There are a number of other species which do this, but I’m don’t have my Sexual Behavior notes here.
Monogamy is noted in many species of birds, mostly the altricial species (those whose chicks require a greater degree of care after hatching). The advantage of monogamy in these species is that the male can provide food and protection after birth. The precocious species (those whose chicks are relatively advanced at hatching) tend to require less investment of time after hatching and therefore the male tends to have more opportunity to ‘fly the coop’ as it were and sow his wild oats abroad.
I’m sure there are other animals that are monogamous, but I haven’t written papers on them.
And while this is a little bit of a wild-ass memory, I think I saw a documentary about an animal that roamed in packs whose old and sickly members would wander off into the wilderness alone to die as opposed to staying with the herd and becoming a liability. While this may not be suicide per se, it’s close enough for me.
Language is a distinctively human trait in that, while you can train a gorilla to use language, humans are the only species with an instinct to acquire and use a language. Children acquire a language instinctively, not because they are taught by their parents or others.