Editing Human evolution (section)

=== The genetic revolution ===

The genetic revolution in studies of human evolution started when [[Vincent Sarich]] and [[Allan Wilson (biologist)|Allan Wilson]] measured the strength of immunological cross-reactions of [[Serum (blood)|blood serum]] [[albumin]] between pairs of creatures, including humans and African apes (chimpanzees and gorillas).<ref name="MolClock">{{Cite journal |last1=Sarich |first1=V. M. |last2=Wilson |first2=A. C. |title=Immunological time scale for hominid evolution |journal=[[Science (journal)|Science]] |volume=158 |issue=3805 |pages=1200–1204 |date=1967 |pmid=4964406 |doi=10.1126/science.158.3805.1200 |bibcode=1967Sci...158.1200S |s2cid=7349579}}</ref> The strength of the reaction could be expressed numerically as an immunological distance, which was in turn proportional to the number of [[amino acid]] differences between homologous proteins in different species. By constructing a calibration curve of the ID of species' pairs with known divergence times in the fossil record, the data could be used as a [[molecular clock]] to estimate the times of divergence of pairs with poorer or unknown fossil records.

In their seminal 1967 paper in ''[[Science (journal)|Science]]'', Sarich and Wilson estimated the divergence time of humans and apes as four to five million years ago,<ref name="MolClock" /> at a time when standard interpretations of the fossil record gave this divergence as at least 10 to as much as 30&nbsp;million years. Subsequent fossil discoveries, notably "Lucy", and reinterpretation of older fossil materials, notably ''[[Sivapithecus|Ramapithecus]]'', showed the younger estimates to be correct and validated the albumin method.

Progress in [[DNA sequencing]], specifically [[mitochondrial DNA]] (mtDNA) and then [[Human Y-chromosome DNA haplogroup|Y-chromosome DNA]] (Y-DNA) advanced the understanding of human origins.{{sfn|DeSalle|Tattersall|2008|p=[https://books.google.com/books?id=Bf4Sitw7YaIC&pg=PA146 146]}}{{sfn|M'charek|2005|p=[https://books.google.com/books?id=n-K436zeUY8C&pg=PA96 96]}}{{sfn|Trent|2005|p=[https://books.google.com/books?id=772BEp8ZyMYC&pg=PA6 6]}} Application of the [[molecular clock]] principle revolutionized the study of [[molecular evolution]].

On the basis of a separation from the [[orangutan]] between 10 and 20&nbsp;million years ago, earlier studies of the molecular clock suggested that there were about 76 mutations per generation that were not inherited by human children from their parents; this evidence supported the divergence time between hominins and chimpanzees noted above. However, a 2012 study in Iceland of 78 children and their parents suggests a mutation rate of only 36 mutations per generation; this datum extends the separation between humans and chimpanzees to an earlier period greater than 7&nbsp;million years ago ([[Year#SI prefix multipliers|Ma]]). Additional research with 226 offspring of wild chimpanzee populations in eight locations suggests that chimpanzees reproduce at age 26.5 years on average; which suggests the human divergence from chimpanzees occurred between 7 and 13&nbsp;mya. And these data suggest that ''Ardipithecus'' (4.5 Ma), ''Orrorin'' (6 Ma) and ''Sahelanthropus'' (7 Ma) all may be on the hominid [[Lineage (evolution)|lineage]], and even that the separation may have occurred outside the [[East African Rift]] region.

Furthermore, analysis of the two species' genes in 2006 provides evidence that after human ancestors had started to diverge from chimpanzees, interspecies mating between "proto-human" and "proto-chimpanzees" nonetheless occurred regularly enough to change certain genes in the new [[gene pool]]:
: A new comparison of the human and chimpanzee genomes suggests that after the two lineages separated, they may have begun interbreeding... A principal finding is that the [[X chromosome]]s of humans and chimpanzees appear to have [[Genetic divergence|diverged]] about 1.2&nbsp;million years more recently than the other chromosomes.
The research suggests:
: There were in fact two splits between the human and chimpanzee lineages, with the first being followed by interbreeding between the two populations and then a second split. The suggestion of a hybridization has startled paleoanthropologists, who nonetheless are treating the new genetic data seriously.<ref>{{cite news |last=Wade |first=Nicholas |author-link=Nicholas Wade |date=May 18, 2006 |title=Two Splits Between Human and Chimp Lines Suggested |url= https://www.nytimes.com/2006/05/18/science/18evolve.html |newspaper=The New York Times |access-date=April 20, 2015 |archive-date=May 18, 2022 |archive-url= https://web.archive.org/web/20220518095858/https://www.nytimes.com/2006/05/18/science/18evolve.html |url-status=live}}</ref>