So this thought occurred to me one morning over the weekend (early in the morning, with the dulcet tones of Baby Boy's screams reverberating around the room):
Is it possible that early in a relationship, when those first few tentative kisses are shared or those two sweaty palms touch for a little sweet hand holding, that both bodies are actually taking a small chemical sample of the other back to the "lab" for analysis?
Could it be that "chemistry" between two people actually is based on chemical compatibility, screened for reproductive fitness from an evolutionary perspective?
It is not necessarily the case that both labs would turn back favorable results; it could be that He is not a good match for Her, but that She is for Him...
The mechanism would also allow for chemical signaling driven by current environmental factors: say that when She sees Him, her pulse quickens in response to 1) His looks, 2) His wittiness, or 3) the sight of Him caring for a puppy...and when they touch, her "interest" is communicated via the chemical exchange.
Of course, the introduction of pheromones to the discussion allows for over the air sampling - you don't even have to touch...