You have to understand a few things first:
1. There is an abundance of men who are single and want female attention.
2. Men generally have low standards. I've seen women who look like michael Clarke duncan in the face being gassed up because "the ass is fat"
3. Factors one and two allow women to be choosy, and look for men who marry looks and personality.
4.Men are viewed as inherently predatory and dangerous.
5. There is less pressure for women to develop a personality and find fulfillment in hobbies that dont involve men or other people in general. Women tend to be more social, but have less to say.
People in general seek people who have attributes they lack. Women have insecurities. They're insecure about their looks, they're insecure about the way society views them so they want confident men. Women are cognizant of the danger that men can pose and feel vulnerable in society so they seek a man who makes them feel safe and secure. Women are afraid of not knowing how to communicate or understand people(part of the reason why women outnumber men in psychology programs in colleges)
A woman can get a vibe from a guy after a few minutes of conversation. The "spark" is when shes able to tell from just a little bit of time that shes talking to a confident, good looking person with a track record of achievement and potential who demonstrates empathy and a high degree of social and emotional intelligence.