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The Major Transitions in Evolution

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.

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The Major Transitions in Evolution

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  1. The Major Transitions in Evolution Eörs Szathmáry Collegium Budapest AND Eötvös University

  2. Units of evolution • multiplication • heredity • variability Some hereditary traits affect survival and/or fertility

  3. 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.

  4. 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

  5. The major transitions (1995) * * * * * These transitions are regarded to be ‘difficult’

  6. 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.

  7. Von Kiedrowski’s replicator

  8. Difficulty 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.)

  9. 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)

  10. 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?"

  11. Units of evolution • multiplication • heredity • variation hereditary traits affecting survival and/or reproduction

  12. Egalitarian and fraternal major transitions (Queller, 1997)

  13. 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

  14. The royal chamber of a termite

  15. Termites

  16. Hamilton’s rule b 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 • APPLIES TO THE FRATERNAL TRANSITIONS!!!

  17. A note on shortcuts and computational irreducibility • If you do not attempt to find a shortcut, you are unlikely to discover one • Pi = 3.1415926…. • The digits never repeat themselves periodically: looks random (normal)  No shortcut (?) • BBP formula (Bailey, Borwein and Plouffe, 1996) • it permits one to calculate an arbitrary digit in the binary expansion of pi without needing to calculate any of the preceding digits • Links to chaos theory  normality?

  18. The origin of insect societies • Living together must have some advantage in the first place, WITHOUT kinship • The case of colonies that are founded by UNRELATED females • They build a nest together, then… • They fight it out until only ONE of them survives!!! • P(nest establishment together) x P(survival in the shared nest) > P(making nest alone) x P(survival alone) • True, even though P(survival in the shared nest) < P(survival alone)

  19. The problem of indiscriminate altruism • An important force: punishment • Worker bees can lay eggs, but they also can be destroyed by other workers • In many polygynous colonies workers fail to wipe out preferentially the kin of the other genetic lines – WHY?

  20. The difficulty of evolving discrimination • “Red beards” exist but seem to be rare • Discrimination must evolve from lack of discrimination • Two types of error reveal asymmetry • (1) you fail to kill a non-relative (decreases your lunch or the lunch of your kin) • (2) you kill your own kin (great price)

  21. 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

  22. 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)

  23. The propagule problem • Some animals can divide, but most develop from an egg • Michod: selection against selfish mutants (cancer-like parasites) • Wolpert & E.S.: cells originating from the same egg speak the same “epigenetic language” • Development is more reliable and evolvable

  24. Epigenetics: a novel inheritance system • Without cell differentiation and its maintenance we would not be here • Passing on of the differentiated state in cell division • “molecular Lamarckism” • Simple organisms: few states • Complex organisms: many states

  25. Genetics and epigenetics Chromatin marking: storage-based system

  26. Gene regulation by autocatalytic protein synthesis • After cell division the regulated state is inherited because enough protein Ais present • An attractor-based system

  27. What makes us human? • Note the different time-scales involved • Cultural transmission: language transmits itself as well as other things • A novel inheritance system

  28. Evolution OF the brain

  29. Fluid Construction Grammar with replicating constructs (with Luc Steels) • selective amplification by linked replication • mutation, recombination, etc.

  30. 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

  31. 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

  32. 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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