For example, the 2R quadrupling of ..
Cosmic censorship hypothesis - Wikipedia
Initial attempts to unravel the evolutionary aspects of our own genome have borne out highly controversial results. Some has suggested that drastic events (2 rounds of whole genome duplication/2R hypothesis) at the base of vertebrate lineage led to the greater genetic complexity in modern vertebrate genome whereas other researchers rejected the 2R hypothesis at all and suggested a continuous mode of small scale duplications (segmental/gene cluster). These alternative scenarios of vertebrate genome evolution are largely based on data from human and few other vertebrate and invertebrate genomes. The recent availability of additional vertebrate and invertebrate genomes has provided an unprecedented insight into the core evolutionary processes that had shaped our genome, deep in the history of life. Surveying of newly sequenced genomes from the deepest branches of life has revealed that many components of the genetic toolkit seen in modern vertebrates arose and diversified deep in animal history even before the origin of chordates. Indeed the origin and evolution of vertebrates is partly accompanied by an increase in gene number, for instance one coherent HOX cluster in amphioxus like invertebrate to four or more HOX clusters in modern vertebrates. However, neither can we take this subtle increase in gene number as an only causative factor for evolution of phenotypic complexity in modern vertebrates nor we can take it as a reflection of whole genome duplication events early in their history. In depth analysis of the genomic data from recently diverged primate species on markedly different phenotypic trajectories provides valuable clues to ancient genomic events. These data supports the notion that small scale duplications and rearrangements have remained a pervasive phenomenon, driving the vertebrate evolution both at phenotypic and genotypic level, throughout their history. I conclude, therefore, that the comparative genomic data from species that diverged early in metazoan evolution (such as Cnidarian-bilaterian) as well as from the very recently diverged animals (such as primates among vertebrates) provides no evidence in favor of the ancestral tetraploidy in vertebrates. In fact it appears that the 2R hypothesis is an artifact, invoked by the lack of phylogenetic breadth in the genome sequence data in early years of genomic era.
10.1139/facets-2017-0063 - FACETS Journal
This is a critical overview of the 2R hypothesis (two rounds of whole genome duplication) on the origin of vertebrates. The conclusion that, to a large extent, is based on the unexpected genomic complexity of organizationally simple animals, such as sea anemone, and on the modest number of 2-fold and, particularly, 4-fold paralogons in vertebrate genomes, is that there is currently no basis to accept the 2R hypothesis. Instead, it is proposed that the vertebrate genome evolved by relatively small, regional duplications.