Is it woman's duty to be beautiful?
Evolutionarily speaking? Possibly. But...there are so many other species out there where the male is the showier of the pair, and it's his duty to attract a mate. For humans, is it the opposite? Maybe a century ago it was man's duty to be the provider and show he was able to provide for a family, and it was woman's duty to look beautiful to show that she was put together and worthy of being courted.
But now...it feels more like it's both men's and women's responsibility to look "beautiful", i.e. put together and all that. Equality is much greater at the current time, so maybe it's not so much of a responsibility solely lain on the shoulders of women.
It still makes me a little sick when I read articles about research that says that women who wear makeup are promoted faster than women who don't. Aren't we all (men and women both) supposed to be judged on merit and the quality of our work, and not the way we dress or how much we spend on makeup and hair each morning?
Yes, it's an instinctual and evolutionary thing-- people will respond more positively to attractive people and people who spend more time on their appearance. It's just frustrating to be in the marginally attractive group and to be someone who hates makeup and doesn't bother dressing well when I'm going to be working (which is pretty much all the time), and to know that if I wore heels and a cute skirt to work it could result in more promotions and raises, even though I'd spend so much more time dealing with the frustrations of crawling under desks in a skirt (and dealing with less than nice comments from coworkers because I'm crawling under desks in a skirt).