The Pros And Cons Of Sexual Selection

Since the fateful day in September 1835, when Darwin first reached the Galapagos Islands, and thereafter began theorizing natural selection, evolution has been a hot topic of debate. Most novices to evolutionary biology believe natural selection, logically, is the driving force of evolution, but what many people forget is the complementary force sexual selection. Sexual selection, as opposed to natural selection, is the passing on of traits that help an organism mate rather than just survive, avoiding environmental dangers and finding food and shelter. Some of the most iconic sexual displays in the animal kingdom include the beautiful feathers of the peahen, the massive claw of the male fiddler crab, or simply becoming the alpha male or female

in an animal population, but some is it possible that some displays are completely invisible? Arguably, one of the most powerful of the phenotypic characters relating to sexual selection is pheromones. Pheromones have had a tremendous impact on evolution through attracting biologically appropriate mates, allowing an organism to stand out in their own populations, while remaining inconspicuous to predators, encouraging, as well as deterring copulation; therefore, controlling the passing of certain traits, and even having an influence on natural selection.
Pheromones are chemical compounds secreted by an organism in an attempt to elicit a response, typically from the same species. These responses can be offensive, defensive, or, most interestingly, sexual. These chemicals are odorless, but once they enter an organism, typically through olfaction, although oral consumption is not uncommon, they cause reactions in the brain, which subconsciously makes another organism react (Gelstein et al., 2011). Pheromones themselves result in very short term actions, but over generations, these results can make big impacts on a species. However, pheromones biggest claim to fame is their effects on human sexuality and attraction.
Members of species that have recently diverged from each other have similarly composed pheromones; this implies that the pheromones diverge along with other phenotypic characteristics. Bombykol, a sex pheromone released by female Bombyx mori, more commonly known as the silkworm moth, is the compound (E,Z)-10,12-hexadecadien-1-ol. The main structural features of this compound are very similar to the sex pheromones of most other female moths and butterflies (Blum, 1977). The typical structure for the majority of this class is a medium-chain length compound with sites of unsaturation and a terminal polar group; in some cases, the only difference between two species is the site of unsaturation. According to Blum (1977), the most closely related species, that is, members of the same genus, sometimes use the same exact substances as their pheromones, with the only difference being that they are in different ratios. Many creatures create multiple chemicals to be used as sex pheromones; these pheromones are synergistic when all chemical are used together.
Occasionally, a member of the species doesn’t produce one or more of the chemicals, these individuals are at a lost, but if an individual of the opposite sex, perhaps does not respond to that specific compound, then these couples’ offspring may soon be attracted only to a new ratio of pheromones. A minute difference in pheromone composition of a small population within a species could be all it takes for this sub group to become sexually isolated from other members of said species; this would eventually lead to more and more divergence until the subgroup is categorized as a new species.
An organism can stand out to mates without having to stand out to predators if they used pheromones to attract mates rather than a flashy appearance.

Evolution, typically, favors vision over olfactory sensation, which implies that a creature will develop keener vision, while olfaction remains the same or even degenerates. With an emphasis put on visionary evolution, it is obvious that, for the most part, animals are not going to evolve in a way that allows them to detect other organisms through pheromone; because of this, it would be beneficial for an organism to stand out with chemosignals because it will allow them to mate without getting caught by predators (Jacobs, 2009). A prime example of this is the whitetail deer. Almost any hunter would attest that covering one’s self in doe urine will attract bucks; this is because, although the doe itself does not possess a fur that would attract mates, she is tan, similar to her surroundings, her urine is filled with pheromones, and this is what truly attracts a father for her young. It would; however, be inappropriate to say that animals never adapt a sense of smell adequate to detect pheromones of another species because it is true, but it occurs far less often than an animal being detected because of its appearance (Blum, 1977). Remaining inconspicuous to predators is beneficial not only to the individual, but also to the species because, without being killed, an animal has more opportunity to pass on its genes and thus

evolve.
Pheromones can both encourage and deter mating; thus, pheromones could affect which genes are getting passed and possibly lead to divergence, in a manner similar to visual sexual displays in other animals. Tears serve as chemosignals, another name for pheromones, in mice; with this in mind, an experiment conducted on humans showed that smelling tears, even though they are odorless, can lower testosterone levels and reduce activity in the sexual arousal area of the brain because of the pheromones found in them (Gelstein et al., 2011). Because of this attribute, an organism can avert reproduction with the use of these chemicals. I. paraconfusus, a species of beetle belonging to the weevil family uses a mixture of naturally produced terpene alcohols as its sexual pheromones. While these chemicals, in a set concentration and ratio, promote mating in this specific species of beetle, it actually inhibits the libido of other Ips species, whom use the same alcohols, if used in the same ratio (Blum, 1977). Realizing that pheromones can assist in sexual aversion, we can assume that the passing on of certain traits could be debilitated by the use of these natural essences.
Pheromones can also be used socially amongst species; this means that pheromones can be utilized in evolution in terms of natural selection. Members of the hymenoptera, which includes bees, wasps, and ants, use pheromones for a great variety of purposes; possibly most notably for social interaction, such as swarming. Another major use of their chemosignals is to notify other members of the colony about discoveries in matters such finding homes and food (Blum, 1977). In this sense, pheromones assist in evolution through the process of natural selection. Individuals who cannot detect these social pheromones are at a disadvantage because they may not be able to follow the colony to resource, which would help them survive, and thus their genes would die out.
Pheromones have many uses in a creature’s society; observers can clearly see that pheromones assists most if not all species in some aspect of their evolution.

To most readers, the biggest interest in pheromones is their effects as aphrodisiacs; turning on one’s neighbor could be as easy as smelling good. Homo sapiens can pass on their genes, such as hair color, eye color, and body shape, through sexual selection, but these genes can be passed on as a secondary characteristic because of the pheromones secreted from potential mates. Not only do pheromones help humans detect potential mates, but also appropriate mates; studies have shown that gay men are more attracted the sweat produced by other gay men rather than the sweat produced by heterosexual men (Kohl, 2006). Humans are also subconsciously repulsed by the pheromones of their close relatives as nature’s way of preventing inbreeding (Pierron, 2013). In the animal kingdom, having the right smell can be the deciding factor in whether or not an animal is able to pass on their genes, the ultimate goal in nature. In human culture, having the right smell can be the deciding factor in whether not a person is able to “get some.” Pheromones could be the main factor in both of these actions, but, luckily for animals, are able to use natural musk, humans on the other hand spend obscene amounts of money on AXE cologne and Chanel #5. Because, as humans and animals know, in the end, it’s all about

sex.