Genomic Drift

Nozawa M, Kawahara Y, Nei M (2007) Genomic drift and copy number variation of sensory receptor genes in humans. Proc Natl Acad Sci USA 104 20421-20426... 

Both articles included comparative studies on ape genomes in an attempt to reveal information on the evolutionary age of polymorphisms. If at a biallelic site one allele is present in the related species, it thought to be the ancestral allele. In most cases the more frequent allele was also the ancestral one, although there were exceptions with the less frequent allele being that of the chimpanzee (this was ascribed to drift... 

Dover underlined that there is no rigid one-to-one relationship between evolutionary mechanisms and environmental processes, but noticed nonetheless that a certain correspondence does exist. He concluded therefore that adaptation is the normal result of natural selection just as exaptation is characteristic of neutral drift, and adoptation is typical of molecular drive. To our purposes, what matters is that we can indeed speak of three mechanisms of evolution the first two are natural selection and neutral drift, while the third mechanism can be called either genomic flux or molecular drive. 

Some moderately repeated DNA sequences are derived from cellular RNAs that were reverse-transcribed and Inserted Into genomic DNA at some time in evolutionary history. Those derived from mRNAs, called processed pseudo genes, lack introns, a feature that distinguishes them from pseudogenes, which arose by sequence drift of duplicated genes. 

Natural selection and genetic drift in genome evolution ... 

Figure 12,2. A. Scheme of negative selection in the conservative mode of evolution. Isochores (solid lines) that drift beyond the GC thresholds indicated by the broken lines are counterselected. B. Scheme of negative and positive selection in the transitional or shifting mode of genomes evolution. Isochores (solid lines) with decreasing GC levels are counterselected, whereas those with increasing GC levels are selected for. (From...

---