After watching my fiancee get horrendously seasick on his parents sailboat this past weekend, I noticed that right before the gastrointestinal pyrotechnics ensued, his lips turned very pale white. This got me thinking. Why are lips red (pink) in the first place? Is the skin more translucent there and we’re just seeing the blood flow? Is the skin itself pigmented and for what evolutionary reason?
Other primates don’t have significantly red or prominent lips.
I’ve long felt that it’s another case of human redirecting sexual signals to the front, as occurred with the development of human female prominent breasts (A point I’ve argued often enough on this Board). The facial lips are analogues of the vaginal lips, in this reading. IIRC, facial lips get warmer and redder when the person is aroused. This would also explain why women paint their lips (and have for a very long time), and why the lips are perceived as a powerful sexual signal.
So why do men have red lips, too?
Is it vestigial, like male nipples?
Another thought: non-white races don’t always have “red” lips either. If there’s a reason for some humans to have red lips, why don’t all humans have red lips (or at least most, ignoring anomalies like albinism, vitiligo, etc.)?
They generally don’t have red vaginal lips, either.
To Serenata67:
For the same reason that different human groups have different skin colors, different hair colors, different hair textures, etc. The mutation which produced whichever trait happened in some places but not in others and/or got favored in some groups but not in others.
No, but their lips are very prominent. For whatever reason, the human lips have evolved to be visually striking, and right now the sexual mimicry explanation is the best we have.
Further question (actually it is mentioned in my OP, but seems to be brushed over)…
HOW do we have red lips? Is the skin pigmented? Is it blood flow that we’re seeing (like a permanent hickey of some sort?) How is it possible for lips to turn white (as my fiancee’s did before chumming the waters this weekend)?
Humans have very few layers of skin on their lips (Wiki says 3-5 layers of skin, vs up to 16 on other skin), so the color of the blood from capillaries under the skin is what shows through. His lips went white because the blood rushed out of his capillaries to the larger vessels, and possibly out of much of the face itself.
I had a childhood friend with a congenital heart problem, who had issues with properly oxygenated bloodflow. Sometimes, her lips would be tinged blue-purple (cyanosis).
I think the thin skin is one reason why lip balms with sunscreen are highly recommended, as your lips don’t have much protection from the sun.
They’re generally a lot less red than women’s lips.
Not to mention men are under the same selective evolutionary pressures from women. If women consistently choose men with a little redness then those genes get passed on. Look at the cover of some fashion magazines or the male roles in chickflick movies. These men tend to lean on the girly side, so there’s definitely something going on with women picking men with some of these characteristics.
Has someone missed the fact that we use lips to communicate? And I don’t just mean speech. If you remove the lips from a picture of a facial expression, good luck trying to figure out what’s intended. All you’ll really have are the eyes. Red lips = more colorful = more noticeable = better for nonverbal communication.
And which parts do women paint? Their lips and their eyes.
And which gender do we associate with being more expressive and emotional? The female.
And which primate does the most communicating with the most members in the most complicated ways? That’s right, us.
Pseudo-vaginas are just a way of missing the obvious.
I knew a guy who had lips that had a distinct yellowish tinge.
His nickname was, you guessed it, Custard Lips
Lips don’t need to evenb exist for verbal communication. If we needed them to be noticeable, they could be more noticeable is dark black, or some other color. But they very closely match the color of vaginal lips.
That’s missing the obvious.
Androgynous characteristics cropped up in another thread recently. The evidence suggests that such features are selected as an indicator of long-term relationship satisfaction, emotional intelligence, and sexual competence and flexibility (Safir et al. 1982; Green and Kenrick 1994).
I disagree. Sexual arousal makes the lips more red not good conversation. Of course, with evolution its usually the case of several different functions, not one, but it seems primarily sexual to me. Also estrogen produces big full lips which advertise reproductive health.
Not to mention we were fucking long before we were talking.
What, you mean grunts don’t count 
Well, yes lips closely match the color of vaginal lips. So do nosebleeds, pimples, and healing wounds. But I don’t think nosebleeds and zits are red because of selection for sexual signaling. They’re red because that’s what color blood is and we’re seeing blood (close to or above the skin) in vaginal lips, nosebleeds, zits, and facial lips.
So it’s not obvious to me that the similar colors are because of sexual signaling. It’s at least as plausible to me that there’s a strong selection pressure for flexible and sensitive lips (since eating and talking are pretty important for humans), which is driving thin skin, leading to a reddish color as a side effect.
It’s also equally plausible to me that the contrasting color of lips is important for visual communication; not just with language (though they’re important for that) but for conveying emotions. I understand that it’s pretty accepted that human facial muscles are more developed than other mammals, and that this is due to human’s use of their facial expressions for signalling. Seems plausible that distinct, highly visible lips could greatly aid that signalling.
I’m not saying that lips play no part in sexual signalling, but I am saying there are certainly plausible theories that explain human lip color without requiring them to be imitation vaginal lips.
(I mean, using the same pop-culture evo-devo reasoning, if lips are pseudo-vaginas, how come I’ve never heard a woman complaining that her boyfriend won’t kiss her on the mouth, but there’s an MS Word auto-complete for ‘How do I get my BF to go down on me?’ Shouldn’t men be equally attracted to putting their faces on both kinds of lips)
There’s an interesting theory about how the peacock’s tail evolved that could also explain why humans have prominent lips.