© Nicholson This article is distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and redistribution in any medium, provided that the original author and source are credited. Cancers are defined by abnormal karyotypes, displaying ever-changing structural and numerical abnormalities. Such plasticity of the karyotype underlies the evolution of cancer cells (Navin et al. 2011, Pavelka, Rancati, and Li 2010, Lee et al. 2011, Nicholson and Duesberg 2009). Karyotype alterations are also responsible for phenotypic variation and evolution in yeast (Rancati et al. 2008, Pavelka, Rancati, and Li 2010) and arguably of species in general (King 1993, McCarthy 2008). Because the alterations in the karyotypes of cancer cells have been shown to be non-random and stable within limits (Li et al. 2009, Nicholson and Duesberg 2009, Gebhart and Liehr 2000, Mertens et al. 1997), recently it has been proposed that carcinogenesis may be a form of speciation (Duesberg et al. 2011, Vincent 2010)