PART I – Nerve Zero, Sexual Pheromones, Nonverbal Communication And Why You Should Avoid Oral Contraceptives
Christopher Philip
This mature buck is checking a “scrape” he and other bucks have left in order to scent check for estrous does.
Animals, much more than people, rely heavily on their sense of smell. As any white-tailed deer hunter will tell you, if you can’t fool his sense of smell, you simply can’t fool him period. But smell means much more to animals than survival, it also means reproduction. The sense of smell is the ticket to longevity through not just one lifetime, but into perpetuity through passing on one’s genes.
One often overlooked form of smell includes the subconsciously acting class called pheromones. These are secret nonverbal cues of communication passed from one sex to another. When female deer enter estrous, as many animals do, they release potent chemical attractants eliciting the pursuit from males over great distances. The lip curl, called “fleming,” passes these scents over specialized cells in their nose. It tells them that love is in the air. Pheromones are particularly potent as mating occurs in just one brief window of time. Other chemical scents provide cues to social status, rank, territories and sex. Animals use scent to identify each other – in animals, scents mark individuals.
Our sense of smell likely influences us in ways that mostly go unnoticed. For example, the areola around a mother’s nipple, upon hearing the crying of her infant, will warm suddenly and release pheromones. These odors are released from tiny bumps around the nipple and researchers have found that the pheromones increase the speed with which infants latch on and begin suckling. They also found that mother’s who secrete more scent also produce children who gain weight quicker.
In another study, researchers found that people preformed better on cognitive tests when they were sniffing the sweat from shirts from individuals who had watched a scary movie rather than those watching a happy movie. However, those sniffing the shirts reported no noticeable conscious difference between the smell of the sweat.
A New Sensory Nerve
Throughout evolution, the sense of smell in humans has lost much of its value – at least on the surface. While people might avoid a nasty smelling food, we have essentially tossed our sense of smell to the curb. However, recent research has uncovered a specialized nerve that promises to bring more attention to our previously thought obsolete sense of smell.
Scientists have labeled this “nerve zero”, or the terminal nerve. It was first discovered over one hundred years ago, but was forgotten and unlabelled. It was usually too small to properly dissect and didn’t attach to any part of the brain as the other nerves did. A dead-end, figured the scientists. Not so, according to new research who examined the dissected nerve zero from a recently deceased whale.
Intriguingly, nerve zero does not attach to the olfactory bulb where smells are analyzed, rather it connects to the brain, specifically to the part of the brain controlling reproduction. Scientists now surmise that never zero bypasses the olfactory cortex, the part of the brain which produces conscious smell. Still scientists believe that it has the capacity to produces non-conscious behavioural patterns likely as a result of sexual pheromones released by potential partners.
Stimulation of nerve zero releases powerful sex hormones gonadotropin-releasing hormone (GnRH) into the blood. GnRH influences a variety of sexual behaviors. Increased levels of GnRH increases sexual body displays in females. When scientists injected white-crowned sparrows and the musk shrew with GnRH they increased copulation solicitation. Shrews increased tail wagging and rump presentation towards males. In males, high levels of GnRH results in an increase in testosterone levels and aggression. Low level of GnRH also has adverse effects on maternal behaviours as shown in mice. In this case, mice where found to leave their pups scattered rather than grouped together.
In many animals, a structure called the vomeronasal organ detects pheromones. In humans, scent cells in our nose connect to the olfactory bulb inside our head. The bulb is a massive relay point containing many synapses. Raw information from over 347 different odor receptors are passed to the olfactory cortex to be analyzed. It is there, finally, that the odors are consciously analyzed. Debate still exists today whether humans still retain their vomeronasal organ with most agreeing that it generally disappears during fetal development although it has been located in nearly half of dissected cadavers despite its minute size.
The Effects Of Sexual Pheromones In Compatibility
Could sexual pheromones work as attractants bringing two people together? In many animals, odors in sweat and urine determine whether sex takes place as these provide vital information about a mate. In humans, it has been shown through research that women find men who carry different histocompatibility complex (MHC) proteins more attractive than when they carry more similar MHCs and that this can be detected through scent alone.
MHC proteins tell the body which cells are theirs and which are foreign. People who have unmatched MHC tend to have higher reproductive fertility so it makes good evolutionary sense to prefer mates who have dissimilar MHC proteins. Genetically different MHC produces offspring with strong immune systems by providing them with a variety of genetic material – it’s why we avoid procreating with members of our family.
Research has shown that women favour the odors of men who have dissimilar MHC. This was found through testing the preferences women had to men who wore a t-shirt over two nights. As a rule, people will tend to be more sexually attracted to those who have MHC’s that are dissimilar to their own mothers. MHC’s also help us find people who are more similar to us, our kin, and help members of families bond to each other.
Continue reading PART II