REPORT ON PHEROMONES
Part 3
Report on pheromones Part 1
Production of sexual pheromones has two different functions for male and female.
Males have the exigency to communicate its own value in order to help the female choosing the better value partner.
For the female the role of pheromones is to communicate her willingness to mate.
Messages communicated through pheromones not only are absolutely reliable because their production depends on the real qualities of the individual, but they are capable to give information that no other signal could give.
For example the largest animal produces more abundant pheromones, the best nourished one produces richer pheromones, the dominant male of a group produces pheromone that only him possesses.
A not banal example that show the complexity that this “honest communication” can reach is that of one species of butterflies and coleopterans that produce or assimilate from plants poisons that protect them from predators. These substances serve the females to protect their eggs and the males produce a pheromone in an amount exactly proportional to their provision of poison. The female chooses the most equipped male that will transfer to her this “wedding gift” during the coupling. Normally the biggest male has also the biggest provision of poison, which insures the female of a bigger progeny more apt to survival and more likely to be chosen by the females for mating. If environmental evolution would change and finding the protective poison became difficult, the ability to find would remain however the first criterion for the female to choose the partner, independently of his size.
Experiments with common rats have revealed that females are attracted by the odorous trace of healthy males and that the trace of males experimentally infected by diseases or parasites lose in attractiveness or became repugnant.
But laboratory experiments reveal that some pheromones allow the animals to recognize its own kin and genetic compatibility, making females prefer (they are always the chooser) males whose immune system is more different and complementary to theirs and to refuse males nearest of kin that have inherited the same immune capacities.
But the recognition of the genetic patrimony through smell goes beyond that.
Mammals have a sequence of DNA called MHC (major histocompatibility complex). This gene underlies the structure their immune system. Rats choose to couple with partner that are different in this gene, in order to let their progeny acquire a greater resistance to diseases.
This was discovered by chance in a laboratory where two strains of genetically identical rats with only one element of the different MHC had been made to reproduce.
The rats preferred to couple with those of the other lineage.
It was easy to arrive to the ascertainment that the sense that allowed to recognize this negligible genetic difference was olfaction.
There are various biological theories to explain how the gene that underlies the immune system is able to condition body smell, but everything let us suppose that also in human beings this smell is able to condition the choice of the partner.
I have many cats that live in our garden, all of them are descendants of only one cat. Any stranger cat coming around is immediately refused. One day we saw arriving a large cat and with surprise I saw my cats smelling it and then leaving it to eat with them. From the spots in his eyes damaged by an old infection we recognized our cat that had disappeared years ago when it was still small.
The mother of all the cats was its sister but she was born after him. No one of the cats had ever known him. It is only its smell that made them recognize their kin relationship.
This shows an other aspect related to the olfactory acknowledgment of the genetic patrimony. In numerous species the members of the same family recognize each other in order to cooperate.
Report on pheromones Part 2
