On Acceleration of Major Transitions in Evolution

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On Acceleration of Major Transitions in Evolution

• Wentian Li1 and Pedro Miramontes2
• 1. Robert S. Boas Center for Genomics and Human
  Genetics, Feinstein Institute for Medical
  Research, North Shore LIJ Health System, NY, USA
• 2. Department of Mathematics, School of Sciences,
  UNAM, Mexico

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This talk
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an astrobiology question (in different forms)

• Whats the probability to have life (lower or
  higher form) on earth?
• Whats the chance that there are other life forms
  (lower or higher) in other galaxies, other
  planets, somewhere in the universe?
• If we rewind the tape of life, then replay, would
  things be different? (in Stephen Jay Goulds
  words)
• Is life on earth inevitable (convergence,
  replicability, predictability, necessity) or an
  lucky event (contingency, chance)?

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Simplistic calculation of the probability

• From A to B, a sequence of events occurred
  (e1, e2, e3).
• If the probability for event e1 to occur is p1,
  that for e2 to occur is p2, then
• P(A? B) p1 p2 p3

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We think the more correct calculation should be

• From A to B, a series of major events
  occurred (e1, e2, e3)
• After a major event occurred, the unit, dynamics,
  mechanism, of evolution was dramatically
  changed
• With the new unit, the conditional probability
  P(e2e1) is very different from the naïve P(e2)
  (higher? acceleration?)
• P(A? B) P(e1)P(e2e1)P(e3e2,e1)

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This issue is relevant to the Evolution vs.
Intelligent Design (ID) debate!
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John Maynard Smith (1920-2004) and Eros
Szathmarys Major Transitions

• Origin of replicator (life)
• From individual replicating molecule to
  protocells, replicating molecules confined to a
  compartment
• From RNA to DNA/protein division of labors
• From bacteria/prokaryotes to eukaryotes with
  organelles
• From asexual clones to sexual reproduction
• From protists to multicellular animals/plants/fung
  i with a developmental body plan
• From solitary individuals to animal colonies
• Emergence of human/language, cultural inheritance
  

I did not include the gene -gt chromosome
transition
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Important features of major transitions

• Almost irreversible. No turning back
• The higher level unit is robust
• Should have benefit
• May take a long time from the
• first event to be widespread
• May have occurred multiple times

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Examples of non-biological unit-changing
transitions

• Computer hardware integrated circuit
• Computer software re-usable functions,
  subroutines, modules
• Language common phrases
• Finance fund of funds
• Business chain stores, franchise
• Scientific research collaboration
• Society group/committee decision-making
• When one says do not reinvent the wheel, the
  higher-leveled, established unit/method/procedure
  is implied!

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Eugene Koonins list of major transitions
(actually, last common ancestors. Tree vs. star
debate)

• Origin of protein folds
• Origin of virus
• Origin of cells
• Origin of major branches of bacteria and archaea
• Origin of major branches of eukaryotes
• Origin of major branches of animals

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Theodore Modis 13 lists of major events in the
history of biology and technology
http//www.growth-dynamics.com/
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Many items in Modis collections are irrelevant
to our purpose

• Big bang (15 billions years ago) Sagan 1
  non-biological
• Oxygen-rich atmosphere developed (2BYA)
  Barrow,Silk 13 external change
• First dinosaurs (290 MYA) Sagan 21 is
  dinosaur important?
• Mass extinctions (280MYA, 66MYA) EncyBritannica,
  9, 13 important in its own right, but still
  external
• Earliest burial of the dead (0.1MYA) Tobias 20
  so?
• Human disappear (?) Boyer 25 no date is
  available!

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500MYA
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Possible criticisms on this scaling plot

• Many major transitions in these lists are
  non-biological
• Invention could be made multiple times,
  independently, at different periods
• selection bias more are known about recent
  history than distant history
• Could be potential impact of mass extinction on
  slowing down evolution?

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Moores law and Kurzweils singularity for
technology

• Gordon Moore (1929-) integrated circuit will
  double the performance every 18 months- 2 years
• Straight line in semi-log plot
• Similar trend in many other technology progresses
  (e.g. hard disk)
• Self-fulfilled prophecy?
• If the (exponential) trend is extrapolated (i.e.,
  if the trend continues forever), physical
  limitation on performance implies a time when
  progress stops (singularity)
• Criticized by Modis the acceleration may only
  be the initial stage, followed by stagnation

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We are more interested in unit-changing,
dynamics-changing, level-of-selection altering
events. So Marnard-Smith/Szathmary (MSS)s list
is most relevant
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MSS1 MT origin of life, replicators

• RNA molecule is the best candidate of initial
  replicator
• Due to poor accuracy, the length of RNA that can
  be a replicator is limited (e.g. 20 bases)
• The potential role of charged surface
  (Wachtershauser)
• Time ? before 3.5 BYA

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MSS2 MT origin of proto-cell, cell-wall

• Lipid bilayer membrane can form naturally in
  water
• Another possible semi-cell was formed with the
  surface at the bottom
• We assume replicators organized within a
  protocell (wall, membrane) have certain
  advantages (high fitness)
• Time ?, before 3.5 BYA

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MSS3 MT origin of DNA/protein split and the
genetic code

• RNA world RNA was both information carrier and
  enzyme
• As RNA-enzyme acquired amino acids as co-factor,
  became a proto translational machinery
• Did genetic code evolve at all?
• Time ? before 3.5 BYA

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MSS4 MT origin of Eukaryotes

• Bacteria losing the rigid cell wall
• The new flexible wall/membrane allowed it to
  swallow (eat/digest)
• Some material being eaten became organelles
  (mitochondria, plastids)
• Time 1.9BYA (Sagan), 2.1 (Britannica, fossil),
  1.7(U.Arizona, protist/green algae), 1.5
  (Heidmann),2.1 (Nelson),

Hedges, BMC Evo Biol (2004), 42
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MSS5 MT origin of sex

• Eukaryote sex most likely made the transition
  from isogamy (e.g. yeasts mating type) to
  anisogamy/oogamy
• Possible early prototype haploid-diploid cycle
  without sex/fusion
• Later on (after the emergence of multicellular
  organism), there is a germ-line and somatic cell
  difference
• Time ?

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MSS6 MT origin of multi-cellular organisms and
body-plan

• Cambrian explosion maybe the presence of a
  predator pushed other animals to have hard shell,
  thus fossil records
• Time 900MYA? 640-540MYA?

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MSS7 MT origin of animal society, social
insects

• Division of labor (similar to that with DNA and
  protein) non-reproductive individuals who
  contribute energy instead of gene pool
• Overlapping generations
• Cooperative care of the young
• Not a physical unit
• Time honeybee(120
• MYA)

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MSS8 MT origin of modern human and language

• Earliest fossil for H.sapiens 0.2 MYA
• Time of language 0.1 MYA
• Did other homo have
• language? Depending on
• its definition
• No anatomical evidence
• (yet) linking language
• exclusively to H.sapiens

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recurrence plot of MSS eight major transitions
x ith MT, y (i1)th MT
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before adding an event
after
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before moving the time
after
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For these 8 major transitions

• After removing the first three MTs (first
  replicators, first protocell, first genetic
  code), the rest 5 MTs have an acceleration trend
  (slope0.56)
• The trend is not as obvious as in Modis plot
  (his list has first mammals, first primate,
  first great apes, first homo, first stone tool,
  debatably, not as major as ours)
• Uncertainties in some datings

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Should we or should we not expect acceleration?

• Once a new unit (new level) was irreversibly
  created, the evolution dynamics should be
  completely new. Whether the marching to the next
  MT is faster or not is not clear, but at least
  different.
• Maybe at the time when a MT first occurred, the
  environment wasnt right to allow it have a
  strong impact?
• What if we miss some other MTs?

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The term acceleration has been used to mean
something else

• Logistic function, sigmoid curve, S-curve..has
  the form f(t) 1/(1e-a-bt)
• The transition from one state
• to another has faster
• (accelerating) changing-rate
• Has been used to describe
• human evolution

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Mass extinctions since Cambrian explosion the
Big Five

• 1. 480 MYA
• 2. 370 MYA
• 3. 250 MYA biggest,
• Permian-Triassic
• 4. 195 MYA
• 5. 65 MYA, 2nd biggest,
• CretaceousTertiary (K-T)

Did mass extinction decelerate the evolution?
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Same recurrence plot with big five marked
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Periodic occurrence (26MY) of mass extinctions
(Raup and Sepkoski, 1984)
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Do we have evidence that mass extinction
decelerate the evolution?

• The mass extinctions with the accurate dating
  were all after Cambrian explosion (550 MYA)
• It is crucial to know whether there were mass
  extinctions between 3.5-2 BYA
• If the hypothesis that mass extinction followed
  periodic pattern, then it shouldnt affect the
  acceleration of major transitions

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Mathematical theories?
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Understanding level-changing major transitions

• Promote cooperation among units
• Similarity among units (kinship)
• Compartment
• Synergetic interactions
• Reciprocal relations (hypercycle)

• Suppress competition between units
• Division of labors
• Fair (game) (e.g. no meiosis distortion)
• Policing by a member
• Self-organization, physical property
• Lower-energy state
• Neighbors, proximity

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Szathmarys stochastic corrector

• Two types of low-level units (1) red replicase,
  helping other to replicate faster, pay a price.
  (2) green selfish
• Compartment/cell (high-level unit) exits.
• Within a cell, green units replicate more
• Comparing different cells, those with certain red
  units replicate more
• Cell splits (or re-mixing)
• Reaching equilibrium

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Prices equation for single-level
(C.C. Li (1912-2003), George Price
(1922-1975))
w3
t
t1
Change of phenotype
Due to selection, i.e., correlation between
fitness and phenotype
Due to transmission bias
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Prices equation for single-level (2nd version)
transmission bias (no w term)
Due to selection, correlation between two
generations
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3rd version Lewontins three conditions for
natural selection
phenotypic change
(3) heritability
natural selection
(2) differential fitness (1) phenotype variation
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Prices equation for two-level systems
unit j in group k
transmission bias
selection at the group level
selection within a group (k)
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Some theoretical works published in physics
journals

• R.Donato (1996), A stochastic model for
  evolution of altruistic genes, J. Physique,
  6445-453.
• Donato, Peliti, Serva (1997), The selection of
  altruistic behaviour, Theory of Biosciences,
  116309-320.
• Silva, Fontanari (1999), Deterministic group
  selection model for the evolution of altruism,
  Euro.Phys.J.B, 7385-392.
• Silva, Fontanari (1999), Stochastic group
  selection model for the evolution of
  altruism,Physica A, 268257-268.
• Alves, Campos, Silva, Fontanari (2000), Group
  selection models in prebiotic evolution,
  Phys.Rev.E, 63011911
• Rozenfeld, Gruver, Albano, Havlin (2006),
  Altruism A natural strategy for enhancing
  survival, Physica A, 369817-822.

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Remaining questions

• Should we consider the emergence of neural
  systems and the emergence of immune systems as
  major transitions? (Further improvement on
  multicellularism)
• How to date the (e.g.) emergence of the field of
  genetics Mendels 1866 paper had no impact,
  only the 3 papers in 1900 generated wider
  interests. Similar dating problems for many MTs.
• The mathematical model above cant answer the
  question about time gap between two major
  transitions, because the low- and high-level unit
  can be anything.

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conclusion

• After each major transition, the level of
  selection (unit), dynamical behavior,.. had
  changed. This change more likely (but perhaps not
  always) led to a comparatively faster pace
  evolving towards the next major transition. Data
  from the last 6 of the 8 major transitions
  compiled by Marnard-Smith and Szathmary show
  evidence for this acceleration. Though one may
  also argue about this being caused by a data
  selection bias.