The pleasure of the women is not even a consideration here.

For many men it's a question of basic math:

1 woman = Good
2 or more = better

Images of two women or one man and two or more women appear in ancient Tantric carvings on temples in India, so the appeal has been with us a long time and transcends culture, so there must be a physiological factor involved as well.

It's a bit presumptuous to assume the image is NOT about the women's pleasure, since it's an ad for a club that men hope will be full of women who want to have sex with them, so alienating the women who might go there is certainly not their goal; they need to attract at least as many women as men for it to be a popular club.

The management is probably aware that a great many women in the hipster club scene have at one time experimented or even periodically 'hook up' with other women, and they often enjoy it very much though they are otherwise heterosexual. The club owners also know men do not do this at anywhere near the same rate, but whether the difference is due to something cultural or biochemical is hard to say.

This ad will definitely attract some (heterosexual) women, to prove how hip they are if nothing else, though many women do genuinely admire other women's bodies in a way heterosexual men don't.

If women were as externally and visually oriented as men are regarding sexual attraction, we'd have ads with men kissing aimed at straight women.

Images of two women or one man and two or more women appear in ancient Tantric carvings on temples in India, so the appeal has been with us a long time and transcends culture, so there must be a physiological factor involved as well.

Slavery has been around for a long time. War too. Are you willing to say that there is a physiological need for these as well?

This ad will definitely attract some (heterosexual) women, to prove how hip they are if nothing else,

Ok, even if we take your claim as fact (which is dubious), this ad is NOT aimed at heterosexual women. If they wanted to target that group wouldn't there be much better ways of doing so other then skin? Just because some people may react to an ad doesn't mean that the ad is targeted to them.

Oh Rich, you need to get out more.

Slavery is in fact still with us as much as ever; war too, so yes I'd say there's some kind of fundamental psychological "need" that these things are filling, though whose needs are being filled is less clear. Aliens didn't introduce slavery, war, and threesomes to humanity, after all. It's all just us, and we're basically the same as ancient Rome, but with cellphones and "free trade agreements."

Nowadays we bring the work to the slaves instead of the other way around so they feel "free" while they do the sweatshop thing. Caribbean "Free Trade Zones" anyone? I say "we" because I'm as much an unintentional part of the problem as you are. Check the labels in your clothes before getting on a soapbox, you might just be benefitting from modern slavery, and the soapbox probably came from a Free Trade Zone.

"...even if we take your claim as fact (which is dubious)..."

Claim? No, it was an observation. Go to a cutting edge, hip club sometime. At some point you will see otherwise "straight" women making out with each other. A female friend of mine has been hit on frequently by very pushy women at these kinds of clubs; I mean they almost wouldn't let her out of the bathroom on one occasion (yes, two of them hit on my friend simultaneously). People who don't go places like that think these are fantasy/ BS statements, but they aren't. She grew out of going to those places, as did I, but many behavioral mysteries are clarified somewhat by direct experience; check it out for yourself.

Remember, the club is trying to attract both men and women who are entirely focused on physical, external appearances and nothing more; that's what "clubbing" is. The owners of these clubs know that, and their profit margins suggest they're correct. They do not care about their marketing's effect on anyone else. They do not want to see anybody loitering at the velvet rope holding a clipboard and asking people questions either, so if you want to know what's really going on inside, you gotta go inside.

Oh Anonymous... how I look forward to your wall of text.

Your word was physiological not psychological. There is a difference despite the words looking similar.

Yes I did say claim. In fact, I chose that word on purpose. You made an observation which in my mind was not sufficiently supported by evidence. So I chose to categorize it as a claim and reject it.

I imagine that my problem was that I was hoping that the individuals behind the ad would be a little more tactical and a little less shallow in their ad. I accept the possibility of you being correct. In my heart I wish you were not.

And in response to your assertion, I have been outside, I remember blearry 5am Sunday mornings with as much fondness as I remember the dippy sorority girls who made out with one another because it would attract the attention of men. In my mind it's a ploy that is on the same level as wearing a giant cowboy hat to a goth bar or carrying a big sign saying "Look at me, look at me!!!"