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GENOME AND EVOLUTION

March 27, 2022

In 1859, Charles Darwin published his famous book "On the Origin of Species". In the book, he proposed three concepts of evolution, heredity, variation and selection without knowing genes and DNA. With development of population genetics in the early 20th century and identification of DNA, this evolutionary theory is widely accepted. The current theory (called the modern synthesis, gradualism or neo-Darwinism) is slow, constant, consistent changes in DNA sequences affect the organism's fitness and subsequently selected. However, several scholars like de Vries and Goldschmidt proposed different views. In addition to gradualism. saltational changes (sudden changes without intermediates) would also be involved in evolution. I agree with Goldschmidt's view (often called 'Hopeful-monster hypothesis') and will test his idea experimentally.

In my analogy, each organism is a unique story. Nucleotides are equivalent to alphabets. Genes are words. Gene regulations are grammar. Words build a sentence (i.e. cell types). Sentences build a paragraph (i.e. tissues). Paragraphs build chapters (i.e. organs). Chapters build a story (i.e. organisms). A story of each species is the genome.

Importantly, a story is written on a physical material like paper (i.e. DNA). Two modes of assembling the story-written papers can be considered; a scroll (in case of prokaryotes) or a book (in case of eukaryotes). A book-style binding (i.e. chromosomes) permits easier changes in the story. During duplication of an original, not only typographical errors in a word or sentence but also incorrect collating, missing and duplicated pages could happen. These could mess up the original story but also create novel ones in rare occasions. I envision all metazoans as distinct edited versions of the same ancestral book/story.

In this view, chromosomal rearrangement (i.e. shuffling pages in a book) is one of essential mechanisms of speciation. It prevents successful meiotic divisions in hybrids establishing reproductive isolation. When it happens, phenotypic differences of a novel species from original parents can vary from no difference to massive differences. The chance of the later case to produce viable offsprings is slim. But in a rare occasion, a novel species emerges as "hopeful monster". Macroevolution is possible without intermediates. Interestingly, this view allows the possibility of 'forking' in addition to 'branching' in phylogenetic trees.

Ref:

Richard Goldschmidt "The Material basis of Evolution" (1940)

Michael J. D. White "Modes of Speciation" (1978)

Philip W. Hendrick "Establishment of Chromosomal Variants" (1980)

de Villena and Sapienza "Female meiosis drives Karyotypic Evolution in Mammals" (2001)

Masatoshi Nei "Mutation-Driven Evolution" (2013)

Stuart Kauffman "The Origins of Order" (1993)