There are many chemical compounds in nature that function to create specific innate responses between members of the same species. These compounds are known as pheromones. Science has demonstrated that pheromones exist in the majority of life forms, from most vertebrates and insects to even the lowest forms of fungi, slime molds, and algae.
The use of pheromones ranges from formation of social groups to coupling behaviors. Many species use them to mark territorial boundaries, trails to resources, locations of danger, and also to encourage proper maturing of young. Of primary interest, however, are sexual pheromones that alter the attraction level of females to males, males to females, and sync females in fertility cycles.
In insects, the earliest studies back in the 1950′s demonstrated that the female silkworm month secretes the chemical bombykol to attract male silkworm months in order to mate. Copepods are another animal that uses pheromones set down by the female to attract males to her. In fact, in nature, the majority of sexual attractant chemicals are created by the female of the species.
Nature studies indicate that there is a division between the types of chemical signals released by each gender. Females tend to trigger sex, epideictic (or avoidance), nursing, and similar young rearing functions. Males tend to trigger aggregation or social behaviors, convey personal species-specific information, and other tasks that may require both genders working together.
The primary use for pheromones in higher animals appears to be the signal of a female ready to breed. In pig populations, a male pheromone spray is used to see which sows are ready for mating by watching their response to the chemical. Because these chemical signals have such a strong role in social settings, it stands to reason that where dominance and pecking order is concerned, that there would be some kind of pheromones playing a role.
Humans, logically, should have pheromones. The issue has not really been if these chemical signals are produced by the body, but rather if the body has some way of detecting them. The majority of mammals have a developed vomeronasal organ, which is actually present in development of the fetus in humans. This organ is atrophied or non-existent in adults however, which has caused disputes among the scientific community. More recently, a second type of receptor was located. This olfactory epithelium is present in humans, and may be how human pheromones are detected.
Regardless, there are enough examples and studies to show that in nature, pheromones do exist. Humans, as mammals, should respond to them. Several studies indicate tantalizing clues that they indeed do, for a number of sexually related functions. Just about any group of women working or living together has experienced the synchronization of their menstrual cycles. This is one aspect of these chemicals in action. A related study shows that males can help regulate those cycles and make them more consistent. These chemicals can be used to attract others, and it has been shown that there are differences in brain activity and hormone response to various pheromone signals.