Most foul odors we smell that give us all a shock of disgust seem to come from bacteria (at least before our mastering of chemistry). We can explain this evolutionarily as a means for making us avoid the most salient disease vectors from our humble origins (excreta, spoiled meat, putrid water, etc.). My question is this, did the selection pressures of evolution act to assign the awful olfactory sensations to the particles emitted by dangerous bacteria and their waste, OR did we evolve the response of disgust to those already-assigned sensations? In other words, does my dog experience a COMPLETELY DIFFERENT SENSATION when smelling (and rolling in) a dead animal - one that's not so bad, or does he experience the smell like I do he just LIKES IT BETTER than I do? I think this question might be about qualia, and whether there's a two-step process in how we perceive them. Do evolving organisms just shift around the few bad smells there are to the stimuli that best deserve them, or are smell sensations and qualia 'fixed' to sources and require a second-step evaluation of the sensation that assigns the "yummy" or "yuk" to the smell? I'm more interested in responses focused on the topic as it relates to philosophy of mind and less about the strict science that I might have gotten wrong. Thanks.