``...central importance to sex was smell...the importance of pheremones...w tend to think of as fairly negligible in terms of sex...'' shag
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I think technically pheremones refer to insects, especially social insects. What you have to do is think of these as molecular signal systems produced by some members of the colony that in turn communicate to other members. The physiological pathway starts in the annena which have specially shaped pores that collect this molecules. The molecules presence against the external cell membranes, trigger a chemical (molecular) action either on the membrane or through the membrane. This starts an internal signal system which locks in some reaction of the insect. It may cause it to produce more of the same substance and extcrete it, or stop producing either.
There is whole system of communication logic manifest through a chemi-mechanical network of internal and external systems. Learning about this stuff is great fun. It sets up a model of how these system work in a general way. So that when you get to mammals urinating on each other for example, you can see how a chemio-mechanical system can work.
For example, mare's in heat dump large quantities of hormones (estrogen, I think) out in their urine. Guess who is goes sniffing around those sites? Mister wanna-get-lucky. So the boys are literally snorting estrogen and getting high and rowdy on it. In other words the female hormone has interacted with the internal male system and turned some key part of their system on, probably to increase or decrease production of other hormones. I would make a strong guess the boys start pissing their pants regularly and other boys are getting themselves worked up over the whole prairie.
The chemical signal systems in reproduction are probably the most reliable because they are direct physio-chemical contact. But it doesn't follow that its the most important. Probably depends alot on the species, genus, family...
As for humans there are interesting problems here we are just as smelly as any dog or cat, but the difference is our noses have less area of contact---hence the magnitude of the effect of a given smell is less....
lunch time thoughts...
CG