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
145
