If you think seriously about life for a moment, the most important thing you need to know is if something is alive or dead. You definitely need this information to date effectively. Here are some pointers taken from science fiction:
1. The object of your attention has to have the ability to recognize your existence. There are various ways to recognize something exists, but the most common way is through eyesight. If you are in the market, it is necessary to examine his / her eyes to see if there is any life. It is a window to the soul thing. You know how it goes, no soul equals no nothing.
2. Does the object of your attention have opposable thumbs??? After all you don’t want the psychological impression that you are being grabbed by the scruff of the neck in those heated moments of deep understanding.
3. Language is very important. There has to be some means of communication. Presumably the object of your affection has mastered the subtleties of "Duh" and is ready to move on. I mean, let’s face it, to be successful, you have to repeat yourself in various ways to maintain the illusion of attention and progress. Sort of the same process used in bringing up children with suitable modifications.
4. Culture is very important. It is a ritualistic way of passing information on to future generations. Sort of a Berlitz book on getting it right. It is also very important in the parent approval process in case you need money for a wedding.
Lastly, there is a rare form of communication that generally happens out of the blue which I like to call the "Duh Factor". It is very difficult to explain without sounding genetically stupid. For those that are unfamiliar with the process it generally goes like this. You’re sitting around, with your brain in neutral. Something happens for no intelligently discernible reason. You, for some undeserving reason have skipped 1 to 4 above. Something that --- and you will have to trust me on this "just is".