The Major Transitions in Evolution

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The Major Transitions in Evolution. Eörs Szathmáry. Collegium Budapest AND Eötvös University. Units of evolution. multiplication heredity variability. Some hereditary traits affect survival and/or fertility. The importance of cumulative selection.
The Major Transitions in EvolutionEörs SzathmáryCollegium Budapest AND Eötvös UniversityUnits of evolution
  • multiplication
  • heredity
  • variability
  • Some hereditary traits affect survival and/or fertilityThe importance of cumulative selection
  • Natural selection is a non-random process.
  • Evolution by natural selection is a cumulative process.
  • Cumulative selection can produce novel useful complex structures in relatively short periods of time.
  • John Maynard Smith (1920-2004)
  • Educated in Eaton
  • The influence of J.B.S. Haldane
  • Aeroplane engineer
  • Sequence space
  • Evolution of sex
  • Game theory
  • Animal signalling
  • Balsan, Kyoto, Crafoord prizes
  • The major transitions (1995)***** These transitions are regarded to be ‘difficult’The importance of cumulative selection
  • Natural selection is a non-random process.
  • Evolution by natural selection is a cumulative process.
  • Cumulative selection can produce novel useful complex structures in relatively short periods of time.
  • Von Kiedrowski’s replicatorDifficulty of a transition
  • Selection limited (special environment)
  • Pre-emption: first come  selective overkill
  • Variation-limited: improbable series of rare variations (genetic code, eukaryotic nucleocytoplasm, etc.)
  • Difficult transitions are ‘unique’
  • Operational definition: all organisms sharing the trait go back to a common ancestor after the transition
  • These unique transitions are usually irreversible (no cell without a genetic code, no bacterium derived from a eukaryote can be found today)
  • Fisher’s(1930) question: the birth of ALife"No practical biologist interested in sexual reproduction would be led to work out the detailed consequences experienced by organisms having three or more sexes; yet what else should he do if he wishes to understand why the sexes are, in fact, always two?" Units of evolution
  • multiplication
  • heredity
  • variation
  • hereditary traits affecting survival and/or reproductionEgalitarian and fraternal major transitions (Queller, 1997)Recurrent themesin transitions
  • Independently reproducing units come together and form higher-level units
  • Division of labour/combination of function
  • Origin of novel inheritance systems Increase in complexity
  • Contingent irreversibility
  • Central control
  • The royal chamber of a termiteTermitesHamilton’s ruleb r> c
  • b:help given to recipient
  • r:degree of genetic relatedness between altruist and recipient
  • c:price to altruist in terms of fitness
  • Formula valid for INVASION and MAINTENANCE
  • Division of labour
  • Is advantageous, if the “extent of the market” is sufficiently large
  • If it holds that a “jack-of-all-trades” is a master of none
  • Not always guaranteed (hermaphroditism)
  • Morphs differ epigenetically
  • Most forms of multicellularity result from fraternal transitions
  • Cells divide and stick together
  • Economy of scale (predation, etc.)
  • Division of labour follows
  • Cancer is no miracle (Szent-Györgyi)
  • A main difficulty: “appropriate down-regulation of cell division at the right place and the right time” (E.S. & L. Wolpert)
  • What makes us human?
  • Note the different time-scales involved
  • Cultural transmission: language transmits itself as well as other things
  • A novel inheritance system
  • Evolution OF the brainFluid Construction Grammarwith replicating constructs (with Luc Steels)
  • selective amplification by linked replication
  • mutation, recombination, etc.
  • Why is often no way back?
  • There are secondary solitary insects
  • Parthenogens arise again and again
  • BUT no secondary ribo-organism that would have lost the genetic code
  • No mitochondrial cancer
  • No parthenogenic gymnosperms
  • No parthenogenic mammals
  • Contingent irreversibility
  • In gymnosperms, plastids come from one gamete and mitochondria from the other: complementary uniparental inheritance of organelles
  • In mammals, so-called genomic imprinting poses special difficulties
  • Two simultaneous transitions are difficult squared: parthenogenesis per se combined with the abolishment of imprinting or complementary uniparental inheritance
  • Central control
  • Endosymbiotic organelles (plastids and mitochondria) lost most of their genes
  • Quite a number of genes have been transferred to the nucleus
  • The nucleus controls organelle division
  • It frequently controls uniparental inheritance, thereby reducing intragenomic conflict
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