Transcript The Major Transitions in Evolution

Mi öröklődik a géneken
kívül?
Szathmáry Eörs
Collegium Budapest
Eötvös University
Units of evolution
1. multiplication
2. heredity
3. variation
hereditary traits affecting
survival and/or
reproduction
The formose ‘reaction’
formaldehyde
autocatalysis
glycolaldehyde
Butlerow, 1861
The reductive citric acid cycle
Von Kiedrowski’s replicator
Peptide replicator networks
Classification of replicators
Limited
heredity
Holistic
formose
Modular
Von
Kiedrowski
Unlimited
heredity
genes
Limited
(# of individuals)  (# of types)
Unlimited
(# of individuals) << (# of types)
King (1980): evolution of the
coenzymes
• He looked at the metabolic maps then
• Coenzymes looked auto- and cross-catalytic
• BUT the situation is slightly more
complicated
• The idea nicely links to the assumed
primitive ancestry of coenzymes (related to
the idea of the RNA world)
An autocatalytic cycle in the given
environment
Although A is autocatalytic, it is not
strictly needed
Dependent on the environment!
Autocatalysis of the pair (A, B) is
more complicated, but easy to see
If this is big, you may not realize the
autocatalysts
The basic question
• Could one kick-start metabolism just with
external molecules and macromolecules
(genes an enzymes)?
• Influx  buildup of metabolism?
Metabolic networks
Membrane heredity
Principle of membrane heredity
Prions
Strain-specific prion propagation
Yeast and fungal amyloid prions
Epigenetic inheritance
1. Structural inheritance (e.g. cortical
inheritance in ciliates)
2. Autocatalytic gene activity
3. Chromatin marking (e.g. methylation)
Genetic and epigenetics
Regulation of gene expression by
constitutive expression of a
protein
• After division the state is inherited because
enough protein is around
Stable and unstable epigenetic
markings
Inheritance of DNA methylation
patterns
Linaria flower inheritance
Linaria (gyújtoványfű)
• A naturally occurring mutant of Linaria vulgaris, originally described
more than 250 years ago by Linnaeus, in which the fundamental
symmetry of the flower is changed from bilateral to radial.
• The mutant carries a defect in Lcyc, a homologue of the cycloidea
gene which controls dorsoventral asymmetry in Antirrhinum.
• The Lcyc gene is extensively methylated and transcriptionally silent in
the mutant.
• This modification is heritable and co-segregates with the mutant
phenotype.
• Occasionally the mutant reverts phenotypically during somatic
development, correlating with demethylation of Lcyc and restoration
of gene expression.
• It is surprising that the first natural morphological mutant to be
characterized should trace to methylation, given the rarity of this
mutational mechanism in the laboratory.
• This indicates that epigenetic mutations may play a more significant
role in evolution than has hitherto been suspected.
Somatic instability of peloric plants
Types of transmitted variation
Language is not Weismannian
soma
germ
soma
germ
protein
DNA
germ
sentence
Neural
germ
representation
protein
DNA
sentence
Neural
representation
Chimpanzee culture
• Each chimpanzee community has its own unique array of traditions
that together constitute the local ‘culture’.
• ‘Customary’ acts are those typical in the community, ‘habitual’ ones
are less common but consistent with social transmission, and ‘absent’
acts are those missing with no apparent straightforward environmental
explanation.
• Traditions are defined as behaviour patterns that are customary or
habitual in at least one site but absent elsewhere.
• Transmission is attributed to social learning on the basis of a complex
of circumstantial evidence, ranging from intense observation by
juveniles to distributions inconsistent with alternative explanations.
The cultures of wild chimpanzees
The different social conventions
of neighbours: the grooming
hand-clasp
Tool-set for harvesting termites
Selective copying
Why is language so interesting?
• Because everybody knows that only we talk
• …although other animals may understand a
number of words
• Language makes long-term cumulative
cultural evolution possible
• A novel type of inheritance system with
showing “unlimited hereditary” potential
Design features of language
• Compositionality (meaning dependent on how
parts are combined)
• Recursion (phrases within phrases)
• Symbolicism (versus icons and indices)
• Cultural transmission (rather than genetic)
• SYMBOLIC REFERENCE and SYNTAX
Three interwoven processes
• Note the different time-scales involved
• Cultural transmission: language transmits itself as
well as other things, has its own dynamics