Spring School in Complexity Science
Introduction to
Complexity Science
Adaptation
Adaptive Complexity
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Seth Bullock, 2006
Terms
Adaptive
1. Flexible, plastic: capable of changing
2. Fit for purpose: evolutionarily adaptive
Adaptation
1. An evolved trait:
2. The process that generates adaptations
3. Also process of change in, e.g., the eye
Adapt, Adaption
To change purposefully: cf chameleon
Adapted
Altered in order to response
Seth Bullock, 2006
Complex Adaptive Systems
Complex adaptive systems come in many forms:
Evolutionary, Neural, Cultural, Linguistic, etc.
Markets, Languages, Brains, etc.
Their hall-mark:
without global co-ordination
organisation comes to reflect environment
Seth Bullock, 2006
Gaia
H: “our planet functions as a single organism that
maintains conditions necessary for its survival”
“Life, or the biosphere, regulates
or maintains the climate and the
atmospheric composition at an
optimum for itself”.
Gaia is not an organism, but “an emergent
property of interaction among organisms”.
What is the claim here? That genes bring about
and maintain global homeostasis?
Seth Bullock, 2006
Fallacies, Misconceptions, etc.
Since adaptive systems almost always combine…
scale
connectivity
non-linear interactions
…they are often complex adaptive systems.
Consequently, adaptive systems are extremely
subtle, and at times, counter-intuitive.
But they are:
the most potent source of biological inspiration
extremely important in their own right
Seth Bullock, 2006
Units of Selection
“We are survival machines—robot vehicles blindly
programmed to preserve the selfish molecules known
as genes. This is a truth which still fills me with
astonishment. Though I have known it for years, I
never seem to get fully used to it” – Richard Dawkins.
Why do we serve genes and not vice versa?
Because genes are replicators
“longevity, fecundity and copying-fidelity”
they, not us, persist across generations
changes to genes, not bodies, are copied
e.g., amputees do not give birth to amputees
Seth Bullock, 2006
Group Selectionist Thought
Dawkins’ work contributed to the debunking of
evolutionary explanations cast at the group level.
Ageing: good for the herd, weeds out stragglers
Sex ratio: efficient for pairing males & females
Communication: the exchange of information
It can be seductive to imagine a
“Groups”:
kind of “selective hierarchy”.
species
ecosystems But “higher” selective pressures
biosphere
are undercut by those below…
organism!
…so genes hold the trump card.
Seth Bullock, 2006
Game Theory
Game theory suggests that global altruism is
unlikely to survive individual selfish interests:
Tragedy of the Commons
a little restraint ensures a common resource for all
Prisoners Dilemma
if both prisoners resist temptation, both go free
Hawk-Dove game
if all play Dove, resources are shared non-violently
In each game, short-termist, individualist, geneeyed behaviour destroys fragile mutualism.
Unfortunately such games are everywhere.
Seth Bullock, 2006
Progress
Short-termist, individualistic, gene-eyed evolution
seems progressive: a march from monad to man.
Seth Bullock, 2006
Evolution ≠ Optimization
But, why would a blind process of random change
+ selection inexorably drive towards… anything?
“our theory of evolution does not
predict an increase in anything”
Progress: change that is directed
and in some sense positive.
Could any
apparent
direction be
an artefact?
Seth Bullock, 2006
Arms Races
Dawkins & Krebs suggested that “arms races”
between coevolving species might drive progress.
During an arms race, “the equipment for
survival, on both sides, is improving”.
But arms races do not spiral upwards.
And surely this is short-term stuff?
Is it, in fact, just adaptation?
More significant, are major innovations: cells, sex,
multi-cellularity, sociality, even language…
Might evolution “never be the same again” after
each “major transition”.
Seth Bullock, 2006
Major Transitions
For Dawkins, major transitions are “watershed
events” in the history of life. They bring about
new ways of being adaptive, new opportunities...
“boosting evolution itself in
ways that seem entitled to
the label progressive”
Once brought about, such
transitions may be difficult
(though not impossible) to reverse, conferring a
“one-way ratchet of of progressive innovation”.
Seth Bullock, 2006
Fitness Landscapes
Central to much reasoning about adaptation is an
iconic visual metaphor: the fitness landscape.

dimensionality
neutrality
locality
passivity
objectivity
Seth Bullock, 2006
“Open-Ended Evolution”
“What features must be present in a system if it is
to lead to indefinitely continuing evolutionary
change?” – Maynard Smith.
Since adaptation is a response to environmental
pressures, some authors suggest that an everchanging environment may be such a feature.
E.g., Co-evolution amongst species…
Additionally, the replicators involved will
necessarily need to be able to build more
complicated (complex?) replicators.
However, still an open(-ended?) question…
Seth Bullock, 2006
Apparent Design ≠ Evolution
“Natural selection is the only known mechanism
capable of effecting the appearance of design.”
In On Growth and Form D’Arcy Thompson argues
that honeycomb structure arises for the same
reasons as spherical bubbles.
What other structures, behaviours, organisations
can be explained in this way?
Seth Bullock, 2006
Constraints vs. Opportunities
Physics and chemistry, then, define, populate and
structure the space of possible adaptations.
Often thought of as “constraints” on evolution.
But it is as accurate to use “enabling” language.
The “morphospace” of available forms seeds
natural selection with self-organising structures.
Is morphospace sparse or densely populated?
Your answer to this question fixes where you sit
on the “self-organisation vs. selection” debate.
Seth Bullock, 2006
Self-Organization vs. Selection
“We stand in the need of a new
conceptual framework that allow us to
understand an evolutionary process in
which self-organization, selection and
historical accident find their natural
places with one another.” – Kauffman.
“Ultra-Darwinists” believe that it is practical to
neglect morphospace considerations.
An opposite position holds that understanding
natural complexity is largely a matter of grasping
the nature of self-organisation.
Seth Bullock, 2006
Evolution To The “Edge of Chaos”
A system cannot exhibit adaptation (via natural
selection) if it tends to either fixity or disorder.
Stasis/Fixity
Complexity
Disorder/Flux
If possible, systems will evolve such that they sit
between fixity and flux: at the “edge of chaos”.
This regime has some interesting properties:
complex patterns, robustness, efficiency
scale-invariant behaviour
but not just adaptive systems
Seth Bullock, 2006
Power Laws
What unites those systems
that exhibit “power laws”?
oak leaf size is normal
solar flare size is not
Is this due to self-organised criticality?
Observed in distributions of earthquakes, firm &
GDP growth, evolutionary extinction, internet
traffic & structure, epidemics, heart arrhythmias…
How long will it be before the power law has as
central a role in science as the normal curve?
Seth Bullock, 2006