Human Pheromones and Brain activation
Some scientists tend to confuse co-existence with cause and effect. It is important to know the difference when discussing brain activation. These three articles help to illustrate the difference.
Cause and effect: The evolved neurophysiological mechanism that allows olfactory/pheromonal input from the social environment of all mammals to activate the brain and cause changes in behavior is detailed in an award-winning journal article that was concurrently published as a book chapter. See: The Mind’s Eyes: Human Pheromones, Neuroscience, and Male Sexual Preferences.
This article provides information about a cause and effect pathway that connects olfactory/pheromonal input (i.e., androstenol) to hormonal changes in the brain. Savic, I. and H. Berglund (2010). “Androstenol – a Steroid Derived Odor Activates the Hypothalamus in Women.” PLoS ONE 5(2): e865
Co-existence: If there is a mechanism that allows visual input from the human social environment to cause changes in behavior, the mechanism is not known to known to exist in other mammals, or in any species.
An unknown mechanism – if it exists — might somehow link visual input to brain activation. Platek, S. M. and D. Singh (2010). “Optimal Waist-to-Hip Ratios in Women Activate Neural Reward Centers in Men.” PLoS ONE 5(2): e9042. If brain activation occurs via this unknown mechanism, it might also be associated with the development of men’s preferences for the visual appeal of a woman’s waist-to-hip ratio (WHR). However, this is a very speculative approach with no support from any animal model.
Besides, the visual link to brain activation associated with development of WHR preferences is not required. Karremans, J. C., E. F. Willem, Willem E., et al. (2010). “Blind men prefer a low waist-to-hip ratio.” Evolution and Human Behavior (in press).
To conclude that a preference for any sexually dimorphic secondary sex characteristic is based on its visual appeal jettisons at least 400 million years of human evolution. Suddenly we favor a consciously perceived signal of fertility/fecundity that requires the visual input. But visual input is not required for the development of the WHR preference in congenitally blind men, or for the development of sexual preferences in any other species of mammal.
Rice, Zhang et al. 2010 links dehydroepiandrosterone (DHEA) to adipose tissue distribution in men. Hormones also determine adipose tissue distribution in women, which allows us to visually differentiate women from men. However, appearance does not directly influence the hormonal changes that are required to link visual input to behavior. Natural body odor does directly effect the hormonal changes that are required to link, via association, olfactory/pheromonal input and appearance to a man’s behavior. This form of non-verbal communication requires no conscious perception, and has been with us since the evolutionary dawn of sexual reproduction (e.g., with yeast).