Evolutionary Theory

The term evolution (and its variants) is widely used in common parlance to denote any gradual or incremental variation, often connoting progress. It is also used analogically or metaphorically by students of history, technology, and development. Population ecologists, among others, have used it to mean any change arising from processes of selection operating on variation occurring in phenomena. Although these uses persist, the stricter Darwinian sense of evolution is “descent with modification.” Descent requires replication, which is now known to occur via the medium of the gene, a process that only occurs in biological reproduction.

The “replication” of ideas, technologies, or organizational forms is a metaphor when writers on these subjects invoke evolutionary concepts.

The logic of biological evolution is unique and compelling. In order to understand this logic, it is important to distinguish between genotype and phenotype. The genotype of an organism is the class to which an organism belongs, which is determined by the physical material made up of DNA that was inherited by the organism from its parents. The phenotype of an organism is the class to which an organism belongs as determined by the physical and behavioral characteristics of the organism—e.g., size and shape, metabolic activity, and so forth. This logic of evolution says that selection mostly does not occur at the level of the genotype, but rather the phenotype. It is individuals and groups that have to survive the pressures of hazardous environments, invasive pathogens, and other predators long enough to be able to reproduce, thereby transmitting their genes to their offspring. Any causal connection between genotype and phenotype is therefore subject to the logic of evolution—those that confer reproductive fitness will be more likely to be replicated; those that impede or that are irrelevant to fitness will become extinct.

This is natural selection—Darwin's great and “dangerous” idea, so-called by the philosopher Daniel Dennett because its inexorable logic is a “universal acid” that burns through to the evolutionary origins of any feature of organic design. To this Darwin added a corollary insight: the concept of sexual selection. It is not enough to have a phenotype that will survive environmental predations. One also needs to have reproductive opportunities of the best quality possible to enhance the probability of one's genes passing through to multiple future generations. The phenotypic expression is the search for mates who bear signs of “good genes” themselves, i.e., they represent the best chances for one's future offspring to survive and prosper. The consequence is a competitive market for mating opportunities in most species, where the most attractive, nurturing, fierce, or well resourced survive. Any quality can be the target of this selection and this depends on the environmental context, its demands and constraints.

This opens the path for coevolution to occur—for reciprocal change to occur in both context and the target. Frequency-dependent selection is one such process—as one type becomes dominant through natural and sexual selection in a population (e.g., tough and dominant individuals) its value decreases and the value of other types (e.g., nurturing and pacific individuals) increases. Population variation can occur around any number of characteristics that attain equilibrium by this comparative advantage, as is visible in our society's profiles of many fitness-relevant characteristics, such as handedness, personality, and body type.

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