Genetics and Evolutionary Biology

Evolution relies on genetic variation within a population. If all members were genetically identical, natural selection would have no variation to act upon, halting the evolutionary process.

Heritability is the part of phenotype variation in a population. This can be attributed to genetic variations in the organisms in that population. This is the factor which describes the chances of evolution occurring in that population on the basis of the genetic differences. 

Physical separation of groups preventing the gene flow between them leads to geographical isolation. Incompatible differences in reproductive structures leading to prevention of cross-fertilization refer to as mechanical isolation. Different periods of attainment of sexual maturity lead to temporal isolation. Hybrid sterility is one of the post-zygotic isolation. Incompatible premating behaviour leading to no attraction between groups for mating is termed as behavioural isolation. Thus, the correct answer is B.

Genetic variation results in the evolution. It results due to mutation in the genetic material resulting in a permanent change. The process of natural selection directly creates genetic variation. Natural selection will change the allele frequencies in the population. This in turn will create genetic variation due to loss of certain alleles during natural selection. Mutation and genetic changes occur spontaneously and change in the environment does stimulate it. The higher the heterozygosity in a population, the higher genetic variation is seen in the population. 

Natural selection is a process governed by changes in environmental factors, these factors produce stress on the organisms. That compels the organisms to undergo changes, in case the organism undergoes changes suitable to the environment, that is, it is suited to survive in the environment will also pass on those traits to the next generation, until the next change occurs. This is natural selection.

An adaptation is a genetic change or variation that provides survival advantage to the organism.

Genetic isolation exists when two populations are so different genetically that they cannot produce fertile offspring (or any offspring at all).
Temporal isolation is genetic isolation achieved due to temporal differences in breeding.
Behavioral

Isolation is a form of reproductive isolation in which two populations

have differences in courtship rituals or other types of behavior that

prevents them from interbreeding

Environmental variations are those variations which are merely due to environment. These variations are temporary and have nothing to do with the next generation. Hereditary variations are those variations which transfer to next generation. Discontinuous variations are sudden changes in organism which are also heritable.

Evolution is the change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes that are passed on from parents to offspring during reproduction.

A subpopulation becomes reproductively isolated from its parental population. It is the formation of species without geographical isolation and these species are called sympatric speciation. It is reproductive, behavioural and temporal isolation.

The biological species concept defines species based on the ability of individuals to interbreed and produce fertile offspring, which is maintained by reproductive isolation from other groups.

Reproductive isolation refers to the mechanisms that prevent two different populations from interbreeding and producing fertile offspring, which is a key step in speciation.

Reproductive isolation acts as a barrier that accelerates the divergence of gene pools, thereby hastening the process of speciation and organic evolution.