which of the following is an acceptable definition of an adaptation among biologists? which of the following is an acceptable definition of an adaptation among biologists? a phenotypic variant that results in the highest fitness among a specified set of variants in a given environment. a derived character that evolved in response to a specific selective agent. a trait that evolved by natural selection for a particular function (because it increases fitness) from an ancestor that did not have that trait. all of these are acceptable definitions.