I think desire or chemistry, or whatever is its own animal, and for me, it leads me wherever it wants to go...anytime. That desire is triggered by differing criteria in different people. i can look at a woman and be completely taken aback how hot she is, but that rarely happens with men. A man can just look at me a certain way and I am done for! Nothing to do with looks. However, on my own in self reflection, I do recognise periods of time when my thoughts are regularly occupied by one type or another, more or less exclusively.