Dont female dogs give off a 'smell' when in heat...I can remember when I was a kid, the lady dogs in the neighborhood, when they went into heat, drove our male dogs nuts...our dogs would lay at the back door, and groan and groan, because they wanted out, and wanted to get at that lady dog....
I remember when we lived next door to a minister, when I had my own kids, and he used to lock his female dog up in a huge outdoor area, completely enclosed by fencing...you could look outdoors anytime of the night or day, and see a pack of male dogs, hanging around, desperate to get into the fenced in area...the minister even had to put fencing on the bottom of the area to prevent the male dogs from digging underneath the fence...
No one told these male dogs that girlie dogs were in heat....they could 'smell' it...
It ain't just dogs, it's most mammals.
IIRC, dog phermones are phenolic derivatives. A dog's nose is up to 1,000,000 more sensitive than a human's (this was in a Science News a few years back), so you bet those guys could smell the lady in heat.
People probably have pheromones too, but our bathing and hygiene procedures tend to cover up these things (soaps, deodorants, perfumes). Have you read Faulkner and the story of the teacher and Eula (the poor guy hugging and sniffing her school chair?)? Napoleone was reported to have said something like this to Josephine in a letter (obviously paraphrased) "I'll be home in a week - don't bathe" Anectdotal, but highly suggestive :)
I am sure others have other tantalizing tidbits along the same lines.
BTW pheromones are used as insect traps commercially - can't remember the insect(s) involved, but it works pretty good.