Editing Human genome (section)

== Evolution ==
{{Human timeline}}
{{See also|Human evolution|Chimpanzee Genome Project}}
[[Comparative genomics]] studies of mammalian genomes suggest that approximately 5% of the human genome has been conserved by evolution since the divergence of extant lineages approximately 200 million years ago, containing the vast majority of genes.<ref name="Mouse2004">{{cite journal | vauthors = Waterston RH, Lindblad-Toh K, Birney E, Rogers J, Abril JF, Agarwal P, Agarwala R, Ainscough R, Alexandersson M, et al. | title = Initial sequencing and comparative analysis of the mouse genome | journal = Nature | volume = 420 | issue = 6915 | pages = 520–562 | date = Dec 2002 | pmid = 12466850 | doi = 10.1038/nature01262 | quote = the proportion of small (50–100 bp) segments in the mammalian genome that is under (purifying) selection can be estimated to be about 5%. This proportion is much higher than can be explained by protein-coding sequences alone, implying that the genome contains many additional features (such as untranslated regions, regulatory elements, non-protein-coding genes, and chromosomal structural elements) under selection for biological function. | bibcode = 2002Natur.420..520W | doi-access = free }}</ref><ref name="ENCODE">{{cite journal | vauthors = Birney E, Stamatoyannopoulos JA, Dutta A, Guigó R, Gingeras TR, Margulies EH, et al. | title = Identification and analysis of functional elements in 1% of the human genome by the ENCODE pilot project | journal = Nature | volume = 447 | issue = 7146 | pages = 799–816 | date = Jun 2007 | pmid = 17571346 | pmc = 2212820 | doi = 10.1038/nature05874 | bibcode = 2007Natur.447..799B }}</ref> The published [[Common chimpanzee|chimpanzee]] genome differs from that of the human genome by 1.23% in direct sequence comparisons.<ref>{{cite journal | author = The Chimpanzee Sequencing Analysis Consortium | title = Initial sequence of the chimpanzee genome and comparison with the human genome | journal = Nature | volume = 437 | issue = 7055 | pages = 69–87 | date = Sep 2005 | pmid = 16136131 | doi = 10.1038/nature04072 | quote = We calculate the genome-wide nucleotide divergence between human and chimpanzee to be 1.23%, confirming recent results from more limited studies. | bibcode = 2005Natur.437...69. | doi-access = free }}</ref> Around 20% of this figure is accounted for by variation within each species, leaving only ~1.06% consistent sequence divergence between humans and chimps at shared genes.<ref>{{cite journal | author = The Chimpanzee Sequencing Analysis Consortium | title = Initial sequence of the chimpanzee genome and comparison with the human genome | journal = Nature | volume = 437 | issue = 7055 | pages = 69–87 | date = Sep 2005 | pmid = 16136131 | doi = 10.1038/nature04072 | quote = we estimate that polymorphism accounts for 14–22% of the observed divergence rate and thus that the fixed divergence is ~1.06% or less | bibcode = 2005Natur.437...69. | doi-access = free }}</ref> This nucleotide by nucleotide difference is dwarfed, however, by the portion of each genome that is not shared, including around 6% of functional genes that are unique to either humans or chimps.<ref>{{cite journal | vauthors = Demuth JP, De Bie T, Stajich JE, Cristianini N, Hahn MW | title = The evolution of mammalian gene families | journal = PLOS ONE | volume = 1 | issue = 1 | pages = e85 | year = 2006 | pmid = 17183716 | pmc = 1762380 | doi = 10.1371/journal.pone.0000085 | quote = Our results imply that humans and chimpanzees differ by at least 6% (1,418 of 22,000 genes) in their complement of genes, which stands in stark contrast to the oft-cited 1.5% difference between orthologous nucleotide sequences | bibcode = 2006PLoSO...1...85D | doi-access = free }}</ref>

In other words, the considerable observable differences between humans and chimps may be due as much or more to genome level variation in the number, function and expression of genes rather than DNA sequence changes in shared genes. Indeed, even within humans, there has been found to be a previously unappreciated amount of copy number variation (CNV) which can make up as much as 5–15% of the human genome. In other words, between humans, there could be +/- 500,000,000 base pairs of DNA, some being active genes, others inactivated, or active at different levels. The full significance of this finding remains to be seen. On average, a typical human protein-coding gene differs from its chimpanzee [[ortholog]] by only two [[amino acid]] substitutions; nearly one third of human genes have exactly the same protein translation as their chimpanzee orthologs. A major difference between the two genomes is human [[chromosome 2]], which is equivalent to a fusion product of chimpanzee chromosomes 12 and 13.<ref>{{cite journal | author = The Chimpanzee Sequencing Analysis Consortium | title = Initial sequence of the chimpanzee genome and comparison with the human genome | journal = Nature | volume = 437 | issue = 7055 | pages = 69–87 | date = Sep 2005 | pmid = 16136131 | doi = 10.1038/nature04072 | quote = Human chromosome 2 resulted from a fusion of two ancestral chromosomes that remained separate in the chimpanzee lineage | bibcode = 2005Natur.437...69. | doi-access = free }}<br />{{cite journal | vauthors = Olson MV, Varki A | title = Sequencing the chimpanzee genome: insights into human evolution and disease | journal = Nature Reviews Genetics | volume = 4 | issue = 1 | pages = 20–28 | date = Jan 2003 | pmid = 12509750 | doi = 10.1038/nrg981 | s2cid = 205486561 | quote = Large-scale sequencing of the chimpanzee genome is now imminent. }}</ref> (later renamed to chromosomes 2A and 2B, respectively).

Humans have undergone an extraordinary loss of [[olfactory receptor]] genes during our recent evolution, which explains our relatively crude sense of [[olfaction|smell]] compared to most other mammals. Evolutionary evidence suggests that the emergence of [[color vision]] in humans and several other [[primate]] species has diminished the need for the sense of smell.<ref>{{cite journal | vauthors = Gilad Y, Wiebe V, Przeworski M, Lancet D, Pääbo S | title = Loss of olfactory receptor genes coincides with the acquisition of full trichromatic vision in primates | journal = PLOS Biology | volume = 2 | issue = 1 | pages = E5 | date = Jan 2004 | pmid = 14737185 | pmc = 314465 | doi = 10.1371/journal.pbio.0020005 | quote = Our findings suggest that the deterioration of the olfactory repertoire occurred concomitant with the acquisition of full trichromatic color vision in primates. | doi-access = free }}</ref>

In September 2016, scientists reported that, based on human DNA genetic studies, all [[Behavioral modernity|non-Africans in the world today]] can be traced to a [[Anatomically modern human|single population]] that [[Recent African origin of modern humans|exited Africa]] between 50,000 and 80,000 years ago.<ref name="NYT-20160921">{{cite news | vauthors = Zimmer C | author-link=Carl Zimmer |title=How We Got Here: DNA Points to a Single Migration From Africa |url= https://www.nytimes.com/2016/09/22/science/ancient-dna-human-history.html |date=21 September 2016 |work=[[The New York Times]] |access-date=22 September 2016 }}</ref>