Gene flow can happen either through hybridization or by exchange of DNA sequence by bacteria or virus. Bacteria and virus have the ability to transfer genes across specie. The gene flow can also result in the formation of a combined gene pool which will have both the characteristics of the two population groups. Thus the barriers to gene flow as well as the gene flow itself, both have the potential to bring about species diversity and take evolution ahead. Genetic drift is the change in the frequency of a DNA sequence, usually called allele. This phenomenon totally depends on chance. When a new member is born in a species, the alleles that will be taken up into the genetic make up of that individual will be through a process of random sampling. And if that individual lives enough to reproduce, only then there is an assurance that the specific alleles in his genes have a scope to survive. It is in this way that the allele frequency changes within a population and this leads to genetic variance within species. Thus a new generation may emerge which may either have lost one genetic trait or may have strengthened one genetic trait of the species, more visibly. Mutations are sudden changes in DNA sequence, of an organism, caused by many factors including, viruses, radiation, mutagenic chemicals, errors during DNA replication, transposition of DNA sequences within the genome, and errors in cell division while sexual reproduction. It has been proved that mutations have a great role in the process of evolution, that is, in the birth of new species, particularly, in smaller life forms like viruses and bacteria. But for higher life forms, mutations are harmful or neutral with respect to the survival of the specie.
2. Race is a social construct rather than a scientific classification. All human beings belong to the species, Homo Sapiens. The concepts and categories of race have not been constant and these have been changing in the history of human kind.