Introduction to Complexity Science

1. Introduction toComplexity Science Adaptation

2. Adaptive Complexity   

3. 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

4. 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

5. “Life, or the biosphere, regulates or maintains the climate and the atmospheric composition at an optimum for itself”. Gaia H: “our planet functions as a single organism that maintains conditions necessary for its survival” 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?

6. 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

7. 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

8. 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 kind of “selective hierarchy”. But “higher” selective pressures are undercut by those below… …so genes hold the trump card. • “Groups”: • species • ecosystems • biosphere • organism!

9. 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, gene-eyed behaviour destroys fragile mutualism. Unfortunately such games are everywhere.

10. Progress Short-termist, individualistic, gene-eyed evolution seems progressive: a march from monad to man.

11. “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? Evolution ≠ Optimization But, why would a blind process of random change + selection inexorably drive towards… anything?

12. During an arms race, “the equipment for survival, on both sides, is improving”. Arms Races Dawkins & Krebs suggested that “arms races” between coevolving species might drive progress. • 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, evenlanguage… Might evolution “never be the same again” after each “major transition”.

13. 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”.

14. Fitness Landscapes Central to much reasoning about adaptation is an iconic visual metaphor: the fitness landscape.  • dimensionality • neutrality • locality • passivity • objectivity

15. “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 ever-changing 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…

16. 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?

17. 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.

18. 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.

19. 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

20. oak leaf size is normal solar flare size is not Power Laws What unites those systems that exhibit “power laws”? Is this due to self-organised criticality? Observed indistributions 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?