Download Does evolution drive toward ever

VCUG3001/VCPG6001 Unravelling Complexity April 2013
Does evolution drive toward
ever-increasing complexity?
Lindell Bromham
Centre for Macroevolution and Macroecology
Evolution, Ecology & Genetics,
Research School of Biology,
Australian National University
www.tempoandmode.com
www.macroevoeco.com
Great
Chain
of
Being
God
Angels
Heaven
Humans
Beasts
Plants
Flame
Rocks
You are here
Sacculina
Sacculina
Sacculina
barnacles
crustaceans
arthropods
language
sociality
Major Transitions
in Evolution
multicellularity
cells
chromosomes
genes
replication
Does this trend indicate a drive toward complexity?
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0
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100
150
Cell type number
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250
Millions of Years before Present
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400
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700
0
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100
150
Cell type number
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250
Millions of Years before Present
200
Genome size
Diversity and complexity increase over time because
uniformity and simplicity must be actively maintained
in the face of inevitable change.
Predicts non-adaptive trend toward complexity
Increase more likely than decrease
More DNA is costly
More DNA is risky
So if more DNA is bad,
why does it accumulate?
R. A. Fisher
In a large population,
selection can promote
tiny advantages and build
adaptation in small steps
Tomoko Ohta
The power of selection
depends on population size
In small populations,
chance effects can lead to
nonadaptive change
‘‘Where, then, is the direct supporting
evidence for the assumption that
complexity is entirely rooted in
adaptive processes? No existing
observations support such a claim,
and, given the massive global
dominance of unicellular species over
multicellular eukaryotes, in terms of
both species richness and numbers of
individuals, if there is an advantage of
organismal complexity, one can only
marvel at the inability of natural
selection to promote it.’’
Michael Lynch
Origins of Genome Architecture
Does gain in complexity = failure to stay
simple?
Complexity is not a measure of success
and does not necessarily convey advantage
Stepwise evolution of complexity is not evidence for a driven trend
Neutral models explain complex patterns using simple processes
Diversity
Availability
Effort
Sheehan PM (1977) Species diversity in the phanerozoic: a
reflection of labor by systematicists? Paleobiology 3:325-328
Arthropoda
Mollusca
Chordata
Platyhelminthes
Nematoda
Annelida
Cnidaria
Echinodermata
Porifera
Bryozoa
Rotifera
Myxozoa
Nemertea
Acanthocephala
Tardigrada
Gastrotricha
Acoelomorpha
Nematomorpha
Brachiopoda
Onychophora
Kinorhyncha
Entoprocta
Sipuncula
Echiura
Hemichordata
Gnathostomulida
Ctenophora
Chaetognatha
Loricifera
Mesozoa
Phoronida
Priapulida
Cycliophora
Xenoturbellida
Placozoa
Micrognathozoa
1
Ecdysozoa
Lophotrochozoa
Deuterostomia
10
100
1000
10000
100000
1000000
Approximate number of described species