Being nice with the expectation of reciprocity is an evolutionary social component that allowed people to better enhance their quality of life and chances for survival by being submissive and/or sharing resources or services with others first. In evolutionary biology and the psychology field, this is called "reciprocal altruism."

Per Wikipedia: "In evolutionary biology, reciprocal altruism is a behaviour whereby an organism acts in a manner that temporarily reduces its fitness while increasing another organism's fitness, with the expectation that the other organism will act in a similar manner at a later time. The concept was initially developed by Robert Trivers to explain the evolution of cooperation as instances of mutually altruistic acts. The concept is close to the strategy of "tit for tat" used in game theory."

Who woulda thoughted that being a "Nice Guy/GirlTM" was a natural phenomenon with a valid function, eh? The wiki link also provides a nice graph that I think everyone should take a look at before commenting because it outlines the process quite nicely and succinctly.

This explanation, of course, completely trashes the previous, unscientific post made about people "learning nice-guy/girl-ness from Anime and popular media."

A thing I've noticed is that people see this overt niceness transaction as manipulative, but also excuse themselves from doing it when they can potentially benefit from it. There are numerous examples that I'm sure everyone can provide regarding guys bending over backwards and providing free services to women and women giving goo-goo-eyed stares and compliments and sex to men in the hopes that they will get a relationship out of it throughout their lives. You've seen it in school when you were younger, and at work when you were older - possibly even within the last month, I'd bet.

Point of the argument is that niceness only matters and it's "tit for tat" nature is overlooked when people are attractive enough. It's only when they're not attractive enough that you'll hear the "Yeah, they're nice, BUT....." responses to why they're not date-able.

Being nice only matters as far as relationships are concerned when you're attractive, and no amount of niceness from man or woman is going to spark attraction where it doesn't already exist.