The question is - which evolutionary adaptation do you wish that humans had developed, and how would it make a difference to your life?
For me it would be chewing the cud. Reason - I tend to eat my food too quickly and end up with indigestion (I blame my parents :)). As a result, I often wish (15-20 min after a meal) that I could regurgitate my food and chew it properly.
I think I was a cow in a previous existance…
Gp
Well, y’know … you -could- do that anyway, it just probably wouldn’t be too pleasant.
I’m torn between the switching gender thing that some frogs can do (it’d be wonderful to be able to flip sides, sneak into the men’s locker room, and learn all their secrets so I could more effectively quash … er … I mean … seduce them!) and the camouflaging ability of the chameleon (for all those times I’ve said something incredibly stupid and wished that nobody could pinpoint it on me) …
Ooh! But if I had the chameleon ability I could just invade the men’s locker room and pretend to be a locker! And I wouldn’t have to spontaneously grow a penis!
Score!
Chameleon abilities. nodsnods That’s my final answer.
Echolocation, like bats. No more stubbed toes when I get up to tinkle in the middle of the night!
Who needs echolocation when you can see in the dark?
Oh, you can’t see in the dark. Oh well.
Wings.
Oh to be able to soar like an eagle!
To ride the thermals like an albatross!
Or perhaps hover like a huming bird!
As a bonus some colorful feathers to go with it. Of course that would open up a hole new industry on feather care products.
I like a nice set of gills on my neck in addition to my lungs. Plus some a set transparant eyelids under the ones I have now. Man I’d spend as much time as I could underwater.
There just have to be mermaids somewhere!
Although I do like NiceGuyJack’s idea except I think I’d be too scared to use them very often.
A prehensile tail. If only my ancestors hadn’t (lost it? never developed it?).
At any rate, there are so many situations where two hands are just not quite enough. You could type and mouse (ala Dilbert), hold several probes and mess with an oscilloscope, etc. It probably wouldn’t be strong enough to take your entire weight, but it’d have to help with climbing and other physical activities too.
I just want to be able to shoot laser beams out of my eyes and crush Tokyo. I’m a simple man.
Feline speed and agility. Obviously.
I wish humans had developed the ability to focus on things moe than 6 feet away from themselves.
What?..Oh!
Well, in that case, I’d like to be able to breathe under water, and/or fly.
Wow. I’m with Bumbazine. Just add one more thing.
Telepathy. 
I’m sure Ma Bell would try to find a way to regulate it though. 
Teleportation.
Or, if we’re restricting ourselves to the somewhat less fantastic…immunity to temperature fluctuations.
Yep, never to feel the cold of a drafty old house again. That’s the thing for me!
I’d kinda like the ability to generate a strong electrical charge. I think that could be kinda fun.
Infrared vision, just like mosquitoes have.
And the ability to tell where someone has been and who they’ve visited by smell.
One thing I’d give up if I could is exceptional hearing. The world is full of annoying transonic squeals that most other humans can’t hear (although it used to be pretty neat when I was younger and could listen to both ends of a telephone conversation from across the room).
I second the prehensile tail. Monkeys rock.
Caiata said
We don’t have any secrets and we’re incredibly easy to seduce. Go ahead, give it a try.
The Vulcan-like ability to be guided by pure logic, with no distracting emotional elements. Not only would it get rid of religion, advertising, politics and a bunch of other problems, but it’d also solve our current world problems by nipping them before they began…
Savage teeth and claws. Not only would we be the smartest kids on the block, but we would also be the meanest and nastiest predators, without the need for “extras”. We could discuss Plato and Aristotle, then when we got hungry, go 'rassle us a buffalo for lunch.
A friend (well, we went to the same High School) of mine used to say that the one modification that he’d make to women would be to insert handlebars into their shoulderblades…
He was more of an aquaintance than a friend…
[Mrs Niggerbaiter]
I never liked him, really
[/Mrs Niggerbaiter]
Gp
Imagine what the world would look like if you had infrared sensors ala snakes, echolocation, and an expanded visual range, all with your brain integrating it into one viewpoint. Oh, the things you could see…
Personally, though, I’d want to ability to regrow lost limbs. I’d make a necklace out of my own middle fingers and wear it around.