Blog 4: Natural Selection vs. Sexual Selection

Natural Selection is the process by which a slight variation in a trait of an individual increases its likelihood of surviving relative to that of an individual not possessing the trait. Fitness describes an organism’s ability to survive and reproduce viable offspring. It is this second component of fitness (production of viable offspring) that gives sexual selection its relevance in terms of evolution. In contrast to natural selection, sexual selection is not dependent on a struggle for existence between individuals, but instead on a struggle between individuals of the same species and sex (usually males) for possession of the other sex.

In the On the Origin of Species, Darwin elucidates on Natural selection when he says: "It may be said that natural selection is daily and hourly scrutinizing, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, wherever and whenever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life." Here he states how Natural Selection is the evolutionary process by which species confer advantages over time and in slight variations. Therefore the slightest differences in structure can turn the scale for the struggle of existence; in turn, individuals possessing advantageous traits will survive and reproduce more. He uses the example of prey hawks and how natural selection gives them. Characteristics of natural selection that differ from sexual selection, by being utilitarian, functional, sensible, economical and constructive.

Sexual Selection is elucidated by Darwin when he discuses “We are, however, here concerned only with that kind of selection, which I have called sexual selection. This depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction.” Here sexual selection is seen as conferring advantages for a particular sex in the SAME species versus the entire population. Its characteristics include showy, elaborate displays that cause a preference for one mate over another and therefore increasing the reproductive fitness of that particular individual who posses that trait. This in turn causes treats preferences as adaptive.

Dawkins takes a similar stance on natural and sexual selection, but tends to make fewer distinctions between the two. He reinforces how the best genes continue and prosper throughout time and are selected for. He further explains since females begin with a disadvantage due to the fact that they invest more in the offspring from fertilization, there in turn must be selective pressure on the males—this comes in the form of sexual selection. Females begin to form preferences for certain males that have certain traits and only those who posses them secure copulations. An example is the domestic-bliss strategy, where females select their males carefully, searching for fidelity and domesticity traits. By insisting a long courtship/waiting period, they weed out casual suitors and only copulates with those who are faithful and will stick around. So here patience is a virtue and their genes for sexual selection will then be passed on to the next generations and will be favored in the gene pool.