Endogenous Retroviruses and Human Evolution
Contributed by: Chris Harrison (University of Texas)
In The Descent of Man and Selection in Relation to Sex, Charles Darwin first suggested that humans shared a common ancestor with the great apes. Now, over a century later, the fruits of molecular biology and comparative genomics have corroborated Darwin’s hypothesis to a stunning degree.
Due to long statistical odds, retroviruses usually infect the DNA of somatic cells and are dubbed exogenous. In the event that a virus integrates itself into a portion of germline DNA, it becomes endogenous and is subject to normal Mendelian inheritance. The co-evolution of the virus and its host entails that the host’s progeny will inherit the virus.
Because of their vertical inheritance, finding the same ERV in two different species offers irrefutable evidence of common ancestry. Genome wide sweeps of the human and chimpanzee genome reveal that we share 7 ERVs with Pan troglodytes, the common chimp (Bonner et al. 1982; Sverdlov 2000; Dangel et al.1995; Svensson et al. 1995; Kjellman et al. 1999; Lebedev et al. 2000; Sverdlov 2000).
This image (courtesy Lavie et al. 2004) confirms the presence of HERV-K(HML-5) homologous sequences in various primate species:
Species abbreviations are as follows:
For Hominoidea, Hsa is Homo
sapiens, Ptr is Pan troglodytes, Ppy is Pongo pygmaeus, and Hla is Hylobates lar
For Old World primates, Cgu is Colobus guereza, Msp is Mandrillus sphinx, and Mmu is Macaca mulatta
For New World primates, Ssc is Saimiri sciureus, Cja is Callithrix jacchus, and Ase is Alouatta seniculus
For prosimians, Nyc is Nycticebus coucang.
Here, we see that HERV-K is present in numerous primate species, indicating that HERV-K was fixed in an ancestral genome whose descendents include all the above species, including Homo sapiens.
The shared ERVs between humans and chimpanzees (as well as other primates) represent one of the most convincing and intriguing arguments for the descent of man. Fossils and comparative anatomy can take us far, but retroviral evidence chronicles the evolutionary history of our species in unprecedented detail.
Bonner, T. I., C. O'Connell, et al. (1982) "Cloned endogenous retroviral sequences from human DNA." PNAS 79: 4709.
Dangel, A. W., B. J. Baker, et al. (1995) "Complement component C4 gene intron 9 as a phylogenetic marker for primates: long terminal repeats of the endogenous retrovirus ERV-K(C4) are a molecular clock of evolution." Immunogenetics 42:41-52.
Kjellman, C., H. O. Sjogren, et al. (1999) "HERV-F, a new group of human endogenous retrovirus sequences." Journal of General Virology 80: 2383.
Lavie L, Medstrand P, Schempp W, Meese E, Mayer J. Human endogenous retrovirus family HERV-K(HML-5): status, evolution, and reconstruction of an ancient betaretrovirus in the human genome. J Virol. 2004;78:8788–8798. doi:10.1128/JVI.78.16.8788-8798.2004.
Lebedev, Y. B., Belonovitch, O. S., Zybrova, N. V, Khil, P. P., Kurdyukov, S.G., Vinogradova, T.V., Hunsmann, G., and Sverdlov, E. D. (2000) "Differencesin HERV-K LTR insertions in orthologous loci of humans and great apes." Gene 247: 265-277.
Svensson, A. C., N. Setterblad, et al. (1995) "Primate DRB genes from the DR3 and DR8 haplotypes contain ERV9 LTR elements at identical positions." Immunogenetics 41: 74.
Sverdlov, E. D. (2000) "Retroviruses and primate evolution." BioEssays 22:161-171.