On which phenotypes of a population does selection pressure that produces evolution operate? Explain the concepts of "fitness" and "adaptation." How do adaptations arise? What are individuals with genes that help them perpetuate themselves in new conditions of existence called?
Selection pressure that produces evolution in a population operates on those structural, physiological, or behavioral phenotypic manifestations of genetically controlled traits that help determine whether an individual is more or less likely to survive to pass on its genes. Genetically controlled traits that increase an organism's fitness, or its probable genetic contribution to succeeding generations, are called adaptations. Thus, adaptations are characteristics that help an organism perpetuate its genes. Adaptations come in a great variety of forms ranging from being genetically uncomplicated to highly complex; from involving in individual cells to whole organ systems; and from being of benefit only under particular circumstances to being of benefit under many different circumstances. Adaptations favoring fitness arise from random mutations to genes, mutations that often have lingered on through many generations before ever proving to be useful to an individual or population. Individuals with genes that help them perpetuate themselves in new conditions of existence are said to be pre-adapted to the new condition.
