This video assumes the viewer has a basic understanding of biology. Works Cited: Bonner, T I. "Cloned Endogenous Retroviral Sequences From Human DNA." Proc Natl Acad Sci U S A 79 (1982): 4709-4713. 19 Oct. 2007 http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=6181510 Crick, Francis. "Central Dogma of Molecular Biology." Nature 227 (1970): 561-563. 18 Oct. 2007 http://www.nature.com/nature/focus/crick/pdf/crick227.pdf Dangel, A W. "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 (1995): 41-52. 19 Oct. 2007 http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=7797267&dopt=AbstractPlus Kjellman, C., H. O. Sjogren, et al. (1999) "HERV-F, a new group of human endogenous retrovirus sequences." Journal of General Virology 80: 2383. http://vir.sgmjournals.org/cgi/content/full/80/9/2383 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) "Differences in HERV-K LTR insertions in orthologous loci of humans and great apes." Gene 247: 265-277. Mitchell, Rick S. "Retroviral DNA Integration: ASLV, HIV, and MLV Show Distinct Target Site Preferences." PLoS Biology 2 (2004): 1127-1137. 18 Oct. 2007 http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15314653 Sverdlov, Eugene D. "Retroviruses and Primate Evolution." BioEssays 22 (2000): 161-171. 18 Oct. 2007 http://www3.interscience.wiley.com/cgi-bin/abstract/69502244/ABSTRACT?CRETRY=1&SRETRY=0 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. ------------------------------ Correction: At 3:39, I meant to say "humans possess 23 chromosomal pairs." Humans possess 46 chromosomes; 23 pairs.

Scientists believe they may be able to explain why people hiccup. Researchers in France have suggested that it may be linked to evolution and the fact that our ancient ancestors lived in the sea. Hiccups are sudden contractions of the muscles used for breathing in. Just after the muscles start to move, the glottis shuts off the windpipe to produce the characteristic "hic" sound. One theory is that the contractions prepare the unborn baby's respiratory muscles for breathing after birth. Another is that they stop amniotic fluid entering the lungs. But neither of these ideas fully stands up. For instance, if hiccups were supposed to keep fluid out of the lungs, it would make more sense for them to involve a cough-like response, not a breath inwards. This latest theory, originally published in the journal BioEssays and reported in New Scientist magazine, says the key to hiccupping lies in a group of animals for whom combining closure of the glottis and contraction of the "breathing in" muscles does serve a clear purpose. They are the primitive air breathers, such as lungfish, gar and many amphibians that still possess gills.