the major transitions in evolution
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/1.jpg)
The Major Transitions in Evolution
Eörs Szathmáry
Collegium Budapest AND Eötvös University
![Page 2: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/2.jpg)
Units of evolution
Some hereditary traits affect survival and/or fertility
1. multiplication
2. heredity
3. variability
![Page 3: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/3.jpg)
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.
![Page 4: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/4.jpg)
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
![Page 5: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/5.jpg)
The major transitions (1995)
***
*
* These transitions are regarded to be ‘difficult’
![Page 6: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/6.jpg)
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.
![Page 7: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/7.jpg)
Von Kiedrowski’s replicator
![Page 8: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/8.jpg)
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.)
![Page 9: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/9.jpg)
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)
![Page 10: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/10.jpg)
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?"
![Page 11: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/11.jpg)
Units of evolution
hereditary traits affecting survival and/or reproduction
1. multiplication
2. heredity
3. variation
![Page 12: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/12.jpg)
Egalitarian and fraternal major transitions (Queller, 1997)
![Page 13: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/13.jpg)
Recurrent themes in 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
![Page 14: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/14.jpg)
The royal chamber of a termite
![Page 15: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/15.jpg)
Termites
![Page 16: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/16.jpg)
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!!!
![Page 17: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/17.jpg)
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?
![Page 18: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/18.jpg)
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)
![Page 19: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/19.jpg)
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?
![Page 20: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/20.jpg)
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)
![Page 21: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/21.jpg)
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
![Page 22: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/22.jpg)
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)
![Page 23: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/23.jpg)
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
![Page 24: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/24.jpg)
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
![Page 25: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/25.jpg)
Genetics and epigenetics
Chromatin marking: storage-based system
![Page 26: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/26.jpg)
Gene regulation by autocatalytic protein synthesis
• After cell division the regulated state is inherited because enough protein A is present
• An attractor-based system
![Page 27: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/27.jpg)
What makes us human?
• Note the different time-scales involved• Cultural transmission: language transmits itself as
well as other things• A novel inheritance system
![Page 28: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/28.jpg)
Evolution OF the brain
![Page 29: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/29.jpg)
• selective amplification by linked replication• mutation, recombination, etc.
Fluid Construction Grammarwith replicating constructs (with Luc Steels)
![Page 30: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/30.jpg)
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
![Page 31: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/31.jpg)
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
![Page 32: The Major Transitions in Evolution](https://reader035.vdocuments.net/reader035/viewer/2022070404/56813b37550346895da40965/html5/thumbnails/32.jpg)
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