Transcript The Major Transitions in Evolution

Darwin for all Seasons
Eörs Szathmáry
Collegium Budapest and Eötvös University
Units of evolution
1. multiplication
2. heredity
3. variability
Some hereditary traits affect
survival and/or fertility
Some majoir transitions are
particularly difficult to explain
• The origin of evolvability in chemistry
• The origin of the genetic code
• The origin of language
The formose ‘reaction’
formaldehyd
e
autocatalysi
s
glycolaldehyde
Butlerow, 1861
Von Kiedrowski’s replicator
SPREAD for replication (von
Kiedrowski)
Classification of replicators
Limited
heredity
Holistic
formose
Modular
Von
Kiedrowski
Unlimited
heredity
genes
Limited
(# of individuals)  (# of types)
Unlimited
(# of individuals) << (# of types)
The main problem of the origin of
life is metabolite channelling
• Enzymes speed up reactions relative to the
unwanted reactions
• Spontaneous decay reactions abound
• Maintenance, not only reproduction,
requires autocatalysis
dx/ dt = k x – d x = 0
Chemical evolution was a race
between tar formation and life
formation
Chemical networks
Life
Tar
•What fraction of planets would end up with just tar?
•What was the role of evolution by natural selection?
Gánti’s chemoton model
metabolism
template
copying
membrane
growth
ALL THREE SUBSYSTEMS ARE AUTOCATALYTIC
Evolution of metabolism: primitive
heterotrophy with pathway innovation
Evolved
enzymatic
reaction
A
A
B
C
B
C
D
D
A
Necessarily heterotrophic
protocell
Assume D is the most
complex
A
B
C
C
B
D
Technology I: evolved nanobots
• In vitro selection of ribozymes is an excellent
example
• Artifical minimal cells for science and technology
• More artificial constructs (e.g. out of DNA)
• Successful copying of connectivity information
• „The first successful examples of nanobots will be
probably similar to some early systems in
biology” (Whitesides)
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
• A novel inheritance system
A simple experiment (Hauser &
Fitch)
• Finite state grammar
(AB)n is recognizable
by tamarins
• Phrase structure
grammar AnBn is
NOT.
• Human students
recognize both:
HOW?
Recuerdos de mi vida (Cajal, 1917,
pp. 345–350)
“At that time, the generally accepted idea that the
differences between the brain of [non-human]
mammals (cat, dog, monkey, etc.) and that of man
are only quantitative, seemed to me unlikely and
even a little offensive to human dignity. . .
but do not articulate language, the capability of
abstraction, the ability to create concepts, and,
finally, the art of inventing ingenious instruments.
..
seem to indicate (even admitting fundamental
structural correspondences with the animals) the
existence of original resources, of something
qualitatively new which justifies the
psychological nobility of Homo sapiens?. . . ’’.
Evolution of the cortex
Ontogenesis of a neuronal network
Neurogenesis AND synaptogenesis
Implementing projections (lock and key)
Variation and selection in neural
development (Changeux)
• There is vast
overproduction of
neurons and synapses
• Transient redundancy
is selectively
eliminated according
to functional needs
Evolution in the brain: some open
questions
• The example of the immune system clearlly shows
that launching a within-organism variationselection mechanism can be adaptive
• There is de novo production of neurons over the
lifespan
• Multiple rounds of survival selection on neurons
generated at different times
• What exactly could be the units of selection
(synapses, neurons, groups, activity patterns)?
• What about the ‘millisecond meme’?
Between linguistic input and
output…
Transmission dynamics in
simulated agents
Technology II: evolved,
communicating agenst
• Communication among autonomous agents would
be very important (rescue operations, planetary
exploration)
• Artificial evolution of nervous systems
(evolutionary robotics)
• The importance of embodiment: autonomous
grounding of emergent semantics