Seriously. Whales don’t have them. Chickens don’t have them. Do we NEED lips?
-L
Well, kisses would suck without them, right? 
I don’t know. I’ve kissed things that weren’t lips before and found it quite enjoyable. Besides, since I’ve always HAD lips, I can’t venture a guess as to what it might be like without them. I’d have a lot of trouble finding a place to put lipstick, i know that much.
No, actually, kisses WOULDN’T suck without them, and neither would we. We use our lips to make the vaccuum seal that enables us to suck on things. Without 'em, babies couldn’t nurse and lovers couldn’t - well, you know.
Nonny
I remember hearing the phrase “He didn’t get those lips from sucking doorknobs,” so I guess that’s what they’re for.
Well, let’s think about this one. How far back down the vertebrate family tree do lips go? Mammals have them. Reptiles have them, but they’re not as flexible as mammals’s.
Some fish have them…oh but wait, back up, duck-billed platypi don’t have lips! But then their mothers don’t have teats either.
Okay, I’m thinking lips have something to do with nursing, but they can also evolve for other purposes.
SexyWriter:
Yeah, but you used your lips (presumably) to do the kissing, so they were still required.
Fiver:
I thought they did. Platypi nurse their young, like all mammals do.
How does this work? Are the baby platypi’s duck bills very flexible? For that matter, cats and dogs don’t have much in the lip department, but they manage to nurse.
Human lips are much fleshier than our ape counterparts. I think I remember Desmond Morris saying the reason for this is to encourage frontal contact (which is also why, according to him, women have needlessly fleshy breasts). Take that for what you think it’s worth.
Holly:
Yes, they nurse their young, but they don’t have teats. They just sort of “sweat” their milk through special pores all over their bellies, and the young’uns lap it up.
I don’t know what baby platypi look like, but presumably they have tongues built for lapping. So they still don’t need lips.
Well Sexywriter, we have lips so that I can kiss Mrs. Infidel all up and down her body.
We also have lips so that Mrs Infidel can give me a great BJ.
I’d think it would have something to do with how they are so sensitive.
Plus they are very manipulatable allowing us to make a large amount of faces.
I think it was also Desmond Morris who hypothosized that it was also made to resemble a human vagina, thus encouraging the contact Holly spoke of.
Ha! Everyone knows the answer is so that our mouths don’t fray at the edges.
Lips serve any number of purposes. They can be used to turn the mouth into a third hand for fine manipulation, they express emotion, they allow us to create a vacuum in our mouths for sucking up water, they are rich in nerve fibres and give us considerable information on the food we are about to swallow. Herbivores particularly are dependant on their lips in gathering food. Watching a horse or even better a camel feed it’s incredible how much their lips act like shortened trunks, picking up food and then passing it into the mouth without it ever touching the teeth. The idea that lips are somehow necessary fro nursing doesn’t make mush sense to me. Anyone who’s ever shoved their finger into the mouth of a suckling animal knows that the suction is created 99% by the action of the tongue and palate. The lips play a fairly minor role.
Paltypi don’t have teats as such. The mammary glands secret milk over faily large patches of the abdomen and the young lick the milk up. The same is true for all monotremes. Whether this is a primitive trait left over from early mammalian ancestors or a secondary characteristic caused by monotremes’ dependance on inflexible electrosensitive bills is open to considerable debate but current opinion seems to favour it being a secondary development from ancestors with teats.
Dogs and cats have just as much in the lip department as people, though the lipstend to curl up rather than down. Just watch a dog snarl sometime and see how big its lips actually are. This is faily common in carnivores where an ability to grab something hard with the entire mouth is more important than an ability to use lips for fine manipulation as is the case with herbivores. As for how they nurse, like most animals dogs and cats suck by moving the tongue under the roof of the mouth to create a vacuum. No lips required.
Not from what I’ve seen of chimpanzees they’re not. Take a look at this picture and tell me you’ve seen a human with lips that fleshy.. Are you sure you don’t mean they have more flexible lips?
We have lips for the same reason other primates have lips. They allow maximal dexterity in maniplulating and working with food and for humans have the added benefit of enhancing voice control by assisting in precise mouth shaping.
I’ve tried and I can’t make M B V or P sounds without using my lips. Fs are hard too. So obviously, we have lips so we can swear at each other.
I just tried to suck on my own finger using just my tongue and palate. Without the lips, it’s completely impossible. You need them to seal the vaccuum, just like I said in the first place.
I can, however, suck with just the lips without using my tongue and palate. It’s not as efficient, but it’s possible.
Nonny
It’s those darn labial consonants like § (b) (m) and (w) that we need lips for. And the labiodentals (f) and (v) need them also, as well as front teeth.
And I’m sure other languages have a whole bunch of other sounds (phonemes?) that require lips or lips and teeth together.
I beg to differ, you can create a vacuum in your mouth with just tongue and palate. That’s how I scratch those itches I get in the back of my mouth.
My roommates must love me, as I just discovered that I can indeed suck on my finger without using my lips. 
Ah well, a day is not a day unless a roommate has looked at me funny.
Nonny, you may be inserting it too far. If you use the tongue to press the finger against the roof of the mouth, you can get a fairly good seal…
Wow, I thought we only had lips so we could whistle and making kissy faces at women:D. Another thing lips help with is keeping the food from falling out of your mouth as you chew it. They keep juices from dribbling down your chin when you take a bite of something juicey, and cover your teeth/keep your mouth closed and sealed too. They are great for eating plants of most kinds too. Do watch animals grazing and you’ll notice that - even bears has great big lips, which can really help when picking berries off bushes… I’ve actually done that where you pull down a branch and just graze all the berries off instead of picking them all by hand, and lips were most helpful - just watch out for bugs! Also watch chimps and orangutangs eating and check out the lip-gymnastics those guys have.
Thanks for straightening me out on the platypus, everyone.
Gaspode:
I guess what I’m trying to say is that human lips, unlike those of any other animal, display the mucous membrane. When chimps aren’t actually using their mouths, the lips appear as more or less of a slit, while human mouths display the pinkish “lip” part. I certainly don’t deny that other animals have useful and often large lips, but I can’t think of one that has lips quite like we do: with the fragile membrane appearing on the lips outside of the mouth.
Is this because the mucous membrane is more flexible than ordinary skin, allowing clearer speech? Does it have more to do with sex, as Morris claims? (It is interesting that throughout time and across the world, women have emphasized their lips with cosmetics to make them appear even more labia-like.)
Having soft, mucous membrane lips does have a drawback: they’re extremely vulnerable to injury. We bite them accidentally, the cold chaps them, sunlight burns them, and when you get punched in the mouth you may have your lip impaled by one of your teeth. Just some lip thoughts.