Twin studies are discussed, as is recent evidence of master genes that may allow chemical communication at the cellular level to play a primary role in behavioral development and in sexual orientation. Genetic conservation among species, specifically with regard to chemical communication, is addressed. Enzymes and chemical responses are linked with human behavior, as are genes and G protein-coupled receptors through an example of familial precocious puberty. Correlates between adrenal androgen metabolism, pheromone production, sexual dimorphism in the human hypothalamus, and human sexual orientation are offered. Chapter 9 details aspects of human consciousness and of limbic learning and memory.
Olfaction plays a key role by providing input to the medial preoptic area of the hypothalamus.
Comparisons and contrasts among species and among theories of consciousness are offered. Alternatively, the gene could encode a protein that influences the regulation of this region by hormones. Effects of pheromones on other species are favorably compared to the effects of putative human pheromones. A consciously-processed odor stimulus has been used as an adjunct to classically condition the human immune response, thereby adding clinical significance to the effects of odors. Examples supporting a link between pheromones and human sexuality are discussed.