Question

How can strong natural selection be acting in a population and yet produce no evolutionary change?

A) This is a trick question; selection always produces an evolutionary change

B) The phenotypic variation on which selection acts is based entirely on environmental variation during development and not based on any genotypic variation so there can be no change

C) We could be looking at allele frequencies near the equilibrium point of a stable polymorphism; selection is acting on genetically controlled phenotypic variation but is merely maintaining the allele frequencies near or at that equilibrium point

D) We could be observing "purifying selection," in which new mutants for a discrete phenotypic trait are constantly being eliminated

E) B) and C) but not D)

F) C) and D) but not B)

G) B), C), and D)

Answer 1

Natural selection acts on the population's heritable traits, not on individual alleles, and selects for individuals with greater contributions to the gene pool of the next generation.

Step-by-step explanation:

Natural selection acts on the population's heritable traits: selecting for beneficial alleles and thus increasing their frequency in the population, while selecting against deleterious alleles and thereby decreasing their frequency—a process known as adaptive evolution.

Natural selection does not act on individual alleles, however, but on entire organisms.

An individual may carry a very beneficial genotype with a resulting phenotype that, for example, increases the ability to reproduce (fecundity), but if that same individual also carries an allele that results in a fatal childhood disease, that fecundity phenotype will not be passed on to the next generation because the individual will not live to reach reproductive age.

Natural selection acts at the level of the individual; it selects for individuals with greater contributions to the gene pool of the next generation, known as an organism's evolutionary (Darwinian) fitness.