Pheromones it turns out are incredibly important in a wide variety of subjects. This was particular noticed in North America where there is a wide variety of insect pests. For example, pretty much everything you grow is ravaged by moths. For the last 150 years or so, their have been strong agriculture and entomology programs all across the US.
One of the big things they worked on was pheromones. So let’s talk about pheromones in humans.
What is a pheromone?
What is NOT a pheromone?
Why expect humans to have pheromones?
What’s wrong with Putative human pheromones?
How should we start again?
A first pheromone?
Unfortunately, the past 25 years of scientific activity has taken us nowhere. So, what is exactly a pheromone? In an animal it is defined as a chemical signal between members of the same species. It is responsible for the communication between the species. It’s the same in all members of a type. All the males of a species produce the same type of molecule. But their may be different amounts. That could be important in mate choices.
The female may go for the male with the most. They all produce basically the same molecule. Pheromones are usually a combination of molecules and not a simple molecule.
What a lot of us have in mind is that pheromones can be something that’s not long-range airborne. So, when the male is hugging the female he is transferring a high molecular protein from his tear ducts over to the nose the female. It can be very short range indeed. Almost a contact pheromone.
What is generally true right away in the animal kingdom is that these molecules are detected right away by the sense of smell. There are a couple that are detected by taste. There is only a small number which is due to the subtlety and the way olfaction works.
The first identification of pheromones was 55 years ago. It was the Silk Moth; Bombay Mori by Adolf Butenandt and team. He spent 20 years trying to identify the moth pheromone. There is a reason it took him so long. And in so doing he created the Gold standard for how you go about studying pheromones now.
So what you have to start with is something you can measure. IN the case of the Silk Moth, the male flutters his wings when he detects the molecules coming from the female. The reason it was a very wise choice to take the domesticated silk moth is because with the chemistry of his time he needed half a million female moths to extract 12mg of his final product. So you need a lot of them and by the end of the project he was importing them by Japan as well as all over around Germany.
You then go through the steps of identifying the molecule and synthesizing what you think the molecule is and then finally creating a bioassay to confirm what it is. This is how you complete the project.
You have to have all of these before you can say you have a pheromone. And it is precisely this that has not been done with humans. So, how do pheromones evolve? Basically, they evolve from any smell that gives information. This leads us to the question … what is the difference between a signal and a cue? The mosquitos are a good way at looking at this.
If we give off smells implying by being, then those smells attract mosquitos. So the mosquitos use the smells as cues. We have not evolved to give those smells off to attract mosquitos. But within a species, smell cues can evolve into signals (pheromones). This is a scenario we can kind of trace with Goldfish.
It was discovered some 30 years ago that many of the female goldfish pheromones are related to our hormones that appear in our blood. So, how did those hormones become pheromones?
Animals are leaky. Hormones leak from mature females. Any males that are sensitive to these cue molecules get to female first. She will lay the eggs, he will fertilize them, but the next generation will be mostly composed of the fastest males. So, you will get selection in the males for greater and greater smell sensitivity and specificity.
So, he starts with a general sense of smell but those receptor molecules become more specialized so you reduce the false alarms so now the receptors will only respond to the particular molecules that are important. Of course, there is also selective advantage which is also advantageous to the female.
Otherwise her eggs are useless. If they are not fertilized then she might as well not even lay them. Now she starts to produce the pheromones to attract the males. So now we have an evolved signaler and an evolved receiver and that is the definition of a signal.
Synthetic elicits same response as the natural stimulus.
All compounds necessary and sufficient.
Only this, these (not similar molecules that animal would encounter)
At realistic/natural concentrations. Some of the work on human pheromones has been done at concentrations a million times the amount in an armpit. Biologically, this is meaningless.
Credible pathway for evolution. You need to be able to make a reasonable story.
What are not pheromones?
Smells are important to humans but not every smell is a pheromone. Let’s take pheromone parties for example. Yes, it’s a smell but it’s individual smells as cues for genetic compatibility. Over a glass of wine you take off the t0shirt that you have been wearing for 3 days and you put I into a numbered bag like the one she is holding up. These are color coded bags an you go for the bag with the gender of your choice. Then you smell the different bags and go with the one that you like. Learn about the top pheromones for guys.
This study was originally done with mice over many years ago. Some Swiss students were persuaded to wear the t-shirts and sniff each other and this became a very famous scientific paper.