Picturing incentive salience
The details of how a metaphorical olfactory/pheromonal “picture’ is generated by electrical signals can be compared to the way color perception is generated because both require sensory input to be transduced to an electrical signal. This picture may be worth a thousand words for comparison.
Instructions for viewing: Stare at the colored dots on this woman’s nose for 30 seconds, then quickly look at a white wall or ceiling (or anything pure white) and start blinking rapidly. (You can click on the picture to enlarge it.)
Your brain processes the image and adds color to the afterimage you see via gene activation in three different receptors for color vision!
In this context, we can compare color vision and the discriminatory power of the brain when it processes olfactory/pheromonal input associated with food odors or pheromones. The comparison depends only on what is known about the complexity of mathematical calculations and self-engineering of genetic changes. This complexity is demonstrated in the discriminatory power of other animals that contain the genomes of species from microbes to man. In no other animal is the response to visual input more important than the response to food odors and pheromones. The molecular basis for the response is the same across all species.
The genomes of cells in organisms appear to self-engineer genetic changes that depend on environmental factors, which include ecological factors. The effect of environmental factors on self-engineered genetic and cellular changes is driven by electrical signals.
The molecular biology of vision
Rods and cones are photoreceptive cells. The absorption of a single quantum of photic energy by only one of the approximately one hundred million molecules of rhodopsin contained in a single cell of a photoreceptive rod is sufficient to generate and transmit an electrical signal. Cones transfer photic energy from a visual signal to an electrical signal, which is perceived as color.
The evolution of three receptors for color vision is largely responsible for the claim that the impact of pheromones on primate behavior has decreased. In theory, the evolution of ecological niches and increased complexity of the social environment caused expansion of the primate cortex and increased intelligence. Theoretically, increased primate intelligence decreased the importance of pheromonal regulation of behavior. According to this theory, color vision became more important to primates, including more highly intelligent humans. However, this theory ignores scientific evidence for the incentive salience of olfactory/pheromonal input across all species from microbes to man.
The molecular biology of olfaction
Like it is with visual input, the incentive salience of other sensory input is directly linked to generation of electrical signals. For example, in humans, odors are chemical signals that are physiologically transduced to electrical signals by receptors in nerve cells of brain tissue. Each of these nerve cells expresses only one of several hundred olfactory receptors.
All possible combinations of a blend of one set of only twenty odors would yield over one million unique mixtures. Although no one has calculated how many odors each of us might be exposed to during our lifetime, it is probably safe to say that many millions of unique mixtures of twenty or more odors are possible. It is conceivable that these mixtures would generate olfactory/pheromonal “pictures” of environmental factors with incalculably more precision than pictures that are commonly associated with color vision.
The incentive salience of odor
Self-engineering of genetic changes enables self / non-self recognition in other organisms that cannot see. This ensures bacteria do not eat their conspecifics. But they are willing to ingest the DNA of heterospecifics, which indicates they recognize the difference between chemical signals from potential food source compared to species specific chemical signals. When no food is available, bacteria respond to species specific pheromones and cease reproduction. Unlike some species, they do not cannibalize each other, and they do not sexually reproduce. When sufficient food enables fertility and sexual reproduction in other species, the pheromones of a potential mate of the opposite sex signal an opportunity for self / non-self sexual reproduction.
The automagical addition of color to the image above is an example of what the nutrition-dependent brains of men and women can do with photic stimuli and three different receptors that generate the electrical signals associated with visual assessment of a photographic image. For comparison, we can only wonder about how much information is processed when odor receptors that number in the hundreds generate electrical signals associated with olfactory/pheromonal assessment of environmental factors associated with the colors we see. But there is little wonder about the relative incentive salience of olfactory/pheromonal compared to visual input.
In mammals, food odors and pheromones cause the electrical activation of genes in hormone-secreting nerve cells of brain tissue. This links them directly to effects on hormones that affect behavior via the required gene, cell, tissue, organ, organ system pathway. Now that you have seen what can be done by your brain with the three receptor that add color to your life, perhaps you can better imagine the role that your mind’s eyes play in the development of behavior associated with hundreds of receptors for olfactory/pheromonal input.
Although you cannot see the olfactory/pheromonal input that electrically activates self-engineered genetic changes, the relative incentive salience of environmental and social factors like food odors and pheromones should be clear. The misrepresentations of cause and effect associated with the evolution of primate color vision should be equally clear.
Primate color vision did not make humans primarily visual creatures because there is no reasonable comparison between the processing power of three receptors for color vision and hundreds of receptors for olfactory/pheromonal input. Simply put, there is no biological basis for a theory about the relative importance of color vision to intelligence, or anything else.
No individual of any species survives without proper nutrition, which is also required for reproduction. Pheromones and food odors are chemical cues that are clearly more important to reproduction than are visual cues in species from microbes to man.
Understanding the incentive salience of sensory input from the environment requires only minimal knowledge of the basic principles of biology and levels of biological organization, which are often misrepresented when researchers link genes or hormones to behavior without indicating what pathway it is that links the required gene activation to the effects on the hormones that affect the behavior. Understanding the difference between gene activation and gene expression is essential to recognizing misrepresentations of biologically based cause and effect.