UK researchers used game theory to model extended animal courtship. Their conclusion: If the courtship process takes longer, it gives the female more time to evaluate the male's potential as father of her offspring.
According to the Science Daily article,
This is another thing that may be moderated by the oxytocin response. Monogamous female mammals, like the prairie vole, need to spend time with a male before they'll mate. I call this rodent dating. Sue Carter has found that blocking oxytocin in a female prairie vole will eliminate her need for this dating period. In the wild, this period would allow the good/bad assessment the researchers are talking about, while allowing her to build social memory of the male via oxytocin -- before she invests in his offspring, and before she develops a monogamous bond.
The human parallel is sooo clear. As I say, anyone can pretend to be great for three dates; a lot of people can pretend to be okay for three months. After that, you see the warts.
And this is why, people, it's a bad idea to have sex on the first date.
Robert M Seymour and Peter D Sozou. Duration of courtship effort as a costly signal. Journal of Theoretical Biology, January 2009