The evolution of Homo sapiens from a primate-like ancestor is quite well understood in contemporary biology. It is now the paradigm of evolutionary biology to know and appreciate the common ancestry shared by the chimpanzees and us. There is still some controversy as to who the last common ancestor was and precisely when it existed, but despite this the hominin vertical descent is fairly well documented through the means of genetics, morphological comparisons and fossil data. Also there is the fact that over 95% of our genome is identical to the great apes (with effectively 99% similarity to the chimpanzees). However this was all very enigmatic and ambiguous until a few years ago and here is why: all the modern great apes contain 48 chromosomes; however the human karyotype consists of 46 chromosomes. If humans and the great apes shared a common ancestor then how could this be so? This simple fact alone, unless proven to the contrary, should have succeeded in repudiating the notion of common ancestry between humans and the apes.
The primate karyotype contains genetic information on every chromosome that the loss of any of them would be fatal, so the loss of two chromosomes cannot be what had happened in our evolutionary history (Miller, 2007). Miller (2007) elucidates that the only possible option is therefore chromosomal fusion and that scientists had been suspecting this for a very long time.
If we recall the structure of a chromosome, it has centromeres in the middle and telomeres on the ends of the structure. If we were to see a fusion we would have to observe two main things: two telomere structures in the middle of the chromosome and two centromeres. An investigation was conducted by Tarjei et al (2005) to try to sequence the chimpanzee genome and to determine whether this fusion actually took place. The definitive results were later published by Tarjei et al (2005) in Nature magazine in 2005 confirming that this fusion did take place, the article reads as follows:
‘Human chromosome 2 resulted from a fusion of two ancestral chromosomes that remained separate in the chimpanzee lineage (chromosomes 2A and 2B in the revised nomenclature, formerly chimpanzee chromosomes 12 and 13); the precise fusion point has been mapped and its duplication structure described in detail.’
The findings which were published clearly demonstrate that the precise fusion point was discovered and the two chromosomes from which it came from, the evidence was unmistakable. Scientists throughout the 90’s published a few journals concerned with the origins of human chromosome number 2 and had experimentally determined the telomeric head to head fusion; however it was not until the recent study in 2005 that we determined that the two chromosomes were also present in the chimpanzees. Not only is this new discovery a great step in discovering the origins of our karyotype but also the origins of our species. This study proved to be a huge step in understanding evolutionary theory and had proved Darwin’s initial prediction that man was descended from the primates.
By Emad Ahangari
Bibliography
• Ijdo J W, Baldini A, Ward D C, Reeders S T, Wells R A, 1991, Origin of human chromosome 2: an ancestral telomere-telomere fusion, http://www.pnas.org/content/88/20/9051.abstract, (Accessed on 20/3/09)
• LaDeana W. Hillier1, Tina A. Graves1, Robert S. Fulton1, Lucinda A. Fulton1, Kymberlie H. Pepin1, Patrick Minx1, Caryn Wagner-McPherson1, Dan Layman1, Kristine Wylie1, Mandeep Sekhon1, Michael C. Becker1, Ginger A. Fewell1, Kimberly D. Delehaunty1, Tracie L. Miner1, William E. Nash1, Colin Kremitzki1, Lachlan Oddy1, Hui Du1, Hui Sun1, Holland Bradshaw-Cordum1, Johar Ali1, Jason Carter1, Matt Cordes1, Anthony Harris1, Amber Isak1, Andrew van Brunt1, Christine Nguyen1, Feiyu Du1, Laura Courtney1, Joelle Kalicki1, Philip Ozersky1, Scott Abbott1, Jon Armstrong1, Edward A. Belter1, Lauren Caruso1, Maria Cedroni1, Marc Cotton1, Teresa Davidson1, Anu Desai1, Glendoria Elliott1, Thomas Erb1, Catrina Fronick1, Tony Gaige1, William Haakenson1, Krista Haglund1, Andrea Holmes1, Richard Harkins1, Kyung Kim1, Scott S. Kruchowski1, Cynthia Madsen Strong1, Neenu Grewal1, Ernest Goyea1, Shunfang Hou1, Andrew Levy1, Scott Martinka1, Kelly Mead1, Michael D. McLellan1, Rick Meyer1, Jennifer Randall-Maher1, Chad Tomlinson1, Sara Dauphin-Kohlberg1, Amy Kozlowicz-Reilly1, Neha Shah1, Sharhonda Swearengen-Shahid1, Jacqueline Snider1, Joseph T. Strong1, Johanna Thompson1, Martin Yoakum1, Shawn Leonard1, Charlene Pearman1, Lee Trani1, Maxim Radionenko1, Jason E. Waligorski1, Chunyan Wang1, Susan M. Rock1, Aye-Mon Tin-Wollam1, Rachel Maupin1, Phil Latreille1, Michael C. Wendl1, Shiaw-Pyng Yang1, Craig Pohl1, John W. Wallis1, John Spieth1, Tamberlyn A. Bieri1, Nicolas Berkowicz1, Joanne O. Nelson1, John Osborne1, Li Ding1, Rekha Meyer1, Aniko Sabo1, Yoram Shotland1, Prashant Sinha1, Patricia E. Wohldmann1, Lisa L. Cook1, Matthew T. Hickenbotham1, James Eldred1, Donald Williams1, Thomas A. Jones2, Xinwei She3, Francesca D. Ciccarelli4, Elisa Izaurralde4, James Taylor5, Jeremy Schmutz6, Richard M. Myers6, David R. Cox6,10, Xiaoqiu Huang7, John D. McPherson1,10, Elaine R. Mardis1, Sandra W. Clifton1, Wesley C. Warren1, Asif T. Chinwalla1, Sean R. Eddy2, Marco A. Marra1,10, Ivan Ovcharenko8, Terrence S. Furey9, Webb Miller5, Evan E. Eichler3, Peer Bork4, Mikita Suyama4, David Torrents4, Robert H. Waterston1,10 & Richard K. Wilson, 2005, Nature Magazine – Generation and annotation of the DNA sequences of human chromosome 2 and 4, http://www.nature.com/nature/journal/v434/n7034/abs/nature03466.html, (Accessed on 19/3/09)
• Miller K, 2007, Ken Miller on Human Evolution – ‘Youtube.com’ (A lecture given by Dr Miller on the origins of human chromosome 2, uploaded to Youtube.com by ‘Kurpalac’), http://www.youtube.com/watch?v=zi8FfMBYCkk, (Accessed on 20/3/09)
• Tarjei S. Mikkelsen, LaDeana W. Hillier, Evan E. Eichler, Michael C. Zody, David B. Jaffe, Shiaw-Pyng Yang, Wolfgang Enard, Ines Hellmann, Kerstin Lindblad-Toh, Tasha K. Altheide, Nicoletta Archidiacono7, Peer Bork, Jonathan Butler, Jean L. Chang, Ze Cheng, Asif T. Chinwalla, Pieter deJong, Kimberley D. Delehaunty, Catrina C. Fronick, Lucinda L. Fulton, Yoav Gilad, Gustavo Glusman, Sante Gnerre, Tina A. Graves, Toshiyuki Hayakawa, Karen E. Hayden1, Xiaoqiu Huang, Hongkai Ji, W. James Kent, Mary-Claire King, Edward J. Kulbokas, III, Ming K. Lee, Ge Liu, Carlos Lopez-Otin, Kateryna D. Makova, Orna Man, Elaine R. Mardis, Evan Mauceli, Tracie L. Miner, William E. Nash, Joanne O. Nelson, Svante Pääbo, Nick J. Patterson, Craig S. Pohl, Katherine S. Pollard, Kay Prüfer, Xose S. Puente1, David Reich, Mariano Rocchi, Kate Rosenbloom, Maryellen Ruvolo, Daniel J. Richter, Stephen F. Schaffner, Arian F. A. Smit, Scott M. Smith, Mikita Suyama, James Taylor, David Torrents, Eray Tuzun, Ajit Varki, Gloria Velasco1, Mario Ventura, John W. Wallis, Michael C. Wend, Richard K. Wilson, Eric S. Lander, Robert H. Waterston, 2005, Nature Magazine – Initial sequence of the chimpanzee genome and comparison with the human genome, http://www.nature.com/nature/journal/v437/n7055/full/nature04072.html, (Accessed on 21/3/09)
Other Readings:
• Darwin C, 1890, The Descent of man, Forgotten Books publishing
• Dawkins R, 1976, The Selfish Gene 30th anniversary edition, Oxford University Press publishing
• Dennett D, 2006, Breaking the spell – religion as a natural phenomenon, Viking (penguin) publishing
• Dennett D, 1995, Darwin’s Dangerous idea – evolution and the meanings of life, Simon and Schuster publishing
• Miller K, 1999, Finding Darwin’s God, Cliff Street Books publishing
