Sex and Mate Selection

and are unicellular. They were likely the first eukaryotes on earth and they carry the genetic material in some cases to undergo meiosis and sexual reproduction. They can undergo sexual reproduction in stressful environmental conditions. Viruses do not mate in the traditional sense but they do mix their DNA and RNA quite effectively, which is a primitive form of mating.

SEX AND MATE SELECTION

Mate selection is one way that evolution can occur in living things. Organisms of many different types will engage in some type of mate evaluation process, which assesses another s fitness and quality. Desirable qualities get passed from one generation to the next through the process of mate selection. In peacocks, for example, there is a certain coloration that increases the likelihood of a female choosing her mate. In many mating systems, there will be one gender that is more selective than the other and the other gender that is more competitive among each other.

There are direct benefits and indirect benefits to being choosy about a mate. Direct benefits include increasing the fitness of the choosy sex because of material advantages of having a certain partner. There may be better territory in one mate, increased ability to care for the young, and better protection from the predators. Indirect benefits include getting higher-quality genes from the potential mate.

There are several mechanisms by which mate selection is done. There can be direct phenotypic benefits, which involve certain traits that can be inherited from one generation to another. Female cardinals preferentially choose a male mate that has the brightest plumage because it is associated with better parenting skills. It also indirectly benefits the offspring, who get fed better.

Sensory bias can also take place. This is seen in certain mating calls in animals and in guppies, who select certain coloration but not for mating purposes. They simply have an affinity for the orange coloration of other guppies.

Another mechanism involves the presence of certain desirous traits that become selfreinforcing, even if it increases the animal s risk for predation or causes increased energy expenditure. Peacock feather coloration is related to this. There is no specific genetic benefit except to have more mates.

There are certain indicator traits that by themselves mean the mate is of a better quality. In humans, this would be seen as a preference for attractiveness. This could mean that a given trait

confers some type of protection against disease or that a certain trait indicates a better ability to get necessary nutrients.

Another mechanism involves genetic compatibility between two potential mates. In some cases, animals can select their mate based on scent. There have been studies in humans indicating that a woman s scent preference for a male depends on what types of genes the man has in relation to the woman. Dissimilar genes are preferred for disease resistance, according to the theory.

In most cases where a preference exists, it is the female that is the choosy sex because she has a greater parental investment compared to the male. This situation can be reversed in some species, especially if there is parental involvement after the birth of the offspring. Species that have this role reversal include seahorses and other fish that involve the female laying eggs into a male brooding pouch. The male raises the young. Male poison-arrow frogs also care for their young and have sex role reversal. Many birds have dual involvement in rearing the young. It has not been documented in mammals.

While we think of mate choice in other animal species, it is also an issue in humans. There are short-term and long-term strategies for selecting a mate. Both males and females have mate choice preferences. They are more similar to one another in humans that exists in other species. Women have preferences for tall men who have beards and a lower voice. Women seek out a mate that has better short-term resources, that have the potential for genetic benefits over another mate, or that will facilitate a breakup with her long-term partner. Women tend to prefer long-term benefits to a mate rather than short-term benefits.

Males have less of an investment in offspring than females and make many more gametes or sperm cells. Men prefer women who will give them a better sexual experience and who are more attractive. They care less about generosity athleticism, intelligence, and honesty in their female partner. They prefer a sexual partner who is more experienced. They are less likely to look at long-term benefits of a female mate but they do look for facial symmetry, commitment, and femininity, which predicts youthfulness. A low waist-to-hip ratio and larger breasts are also preferred.