Evolution and computation
DOI link for Evolution and computation
Evolution and computation book
Changes arise in the genome by mutation, often as ‘copy errors’ during transcription, when the sequence may be shuffled or some modules repeated by mutation. The changed genome in turn produces changes to physical form or phenome. Most mutations are either neutral or harmful to the living form, and beneficial mutations are rare. Differentiation during the development of an individual is controlled by the homeobox genes (originally discovered in the fruit fly Drosophila) that turn other genes on or off during development, controlling the order of morphogenesis and the position of different parts in relation to the body plan. In the case of the fruit fly, the mutation of a single gene, known as antennapedia, produces changes to the morphology and function of the fly’s antenna, so that it develops as a leg rather than an antenna. This is possible because all cells in the fly have all of the information necessary to become leg cells or antennae. Every cell in an organism carries a complete genome, all of the information necessary for the development of the complete organism. Antennapaedia and its homologues control limb development in all vertebrates, so that the forelimbs of birds develop as wings, or the extremities of the forelimbs develop as hands in humans or flippers in seals. Homeobox sequences have been conserved throughout evolution and are controlling factors to the development of even distantly related organisms. Changes to the homeobox genes have substantial effects on the morphology
of individuals, and when these changed individuals survive the rigours of natural selection, new descendant species are formed. If individual mutations offer the advantage of superior functionality in some capacity, then the mutant organism will have an enhanced reproductive fitness. If its progeny inherit the changed genome, then evolutionary change will occur. Differentiation by speciation, new species arising from a common ancestor, is normally described in phylograms, or tree-like charts. The underlying logic is to plot the sequence of morphological differentiations that lead from the ‘form’ of a common ancestor to the multiple differentiated forms of the whole group or taxa. For example, the common ancestor of all arthropoda, including crustaceans, centipedes, spiders, scorpions and insects, was a simple tube-like worm. The arthropoda group has over one million species alive today, with a fossil record that starts in the early Cambrian era, and it accounts for over 80 per cent of all known organisms. The sequence of morphological differentiation produced segmented bodies, exoskeletons and jointed legs. The co-option or recruitment of existing genes into new organisations means that no new molecules are needed, so that repetition and reconfiguration produce a higher complexity within the genome. Living forms have an anatomical and spatial organisation that con - sists of repeated modules that vary in size,
shape and number. The genome too is modular in organisation, consisting of many repeating sequences arrayed in distinct groups, each of which may contain common or multiple sequences that also occur in other groups. If small changes occur in the regulatory genes, they have the potential to produce changes to the size, shape and number of repeating modules in the living form. Over evolutionary time the genome has grown in size and complexity, but there is no apparent correlation between the size of the genome and the complexity of a living form. It has been observed that large living forms with very large genomes, such as trees in temperate climatic regions, tend to produce variant descendant species less often than other species. In the history of biological evolution, the emergence of small complex anatomical organisations made possible the emergence of ever larger and even more complex organisations. Complexity builds over time by a sequence of modifications to existing forms. There is both fossil and genetic evidence that the emergence of the general vertebrate organisation, and its subsequent modification into amphibians, reptiles, birds and mammals, occurred in this sequence.