the evolution of identity and modularity in nature...
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The Evolution ofIdentity and Modularity
in Nature and ComputationLee Spector
Cognitive ScienceHampshire College
Tuesday, April 16, 13
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Overview
• Modularity
• Identity
• Evolving computer programs
• Evolving modular programs
• Implications
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Modularity is Everywhere
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http://equitygreen.typepad.com/blog/2007/08/hybrid-seattle-.html#more
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http://www.flickrfotos.com/modular-44-plastic-coffee-table-design/
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http://talkinterior.com/interior-design-vita-minimalist-modular-home/
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http://www.e-potpourri.com/index.php/2008/02/02/octopus-studios-silverfish-aquarium-boasts-modern-modular-design/
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http://wyss.harvard.edu/viewevent/37/wyss-seminar-series-kasper-stoyhttp://www.technovelgy.com/ct/Science-Fiction-News.asp?NewsNum=953
http://www.engadget.com/2005/03/26/m-tran-self-reconfigurable-modular-robot/http://www.hizook.com/blog/2012/01/16/ted-talks-about-robots-and-robotics-part-1
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http://www.synthtopia.com/content/2007/04/04/moog-55-modular-synthesizer/
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http://mappery.com/map-of/Tokyo-Metro-Map
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Modularity in Software
• Pervasive and widely acknowledged to be essential
• Modules may be functions, procedures, methods, classes, data structures, interfaces, etc.
• Modularity measures include coupling, cohesion, encapsulation, composability, etc.
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http://en.wikipedia.org/wiki/File:Sa-fern.jpg
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http://a-z-animals.com/animals/centipede/
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Cognitive Science• Long history of modularity theories: Gall, ...
Simon, ... Fodor, ... Cermak and Craik, ... Gardner, ... Jackendoff, ... Grafman, ...
• Simon’s “nearly decomposable systems”
• Fodor’s features: domain specific, mandatory, fast, encapsulated, fixed architecture, characteristic patterns of ontogeny and failure
• Central vs. input systems
• Modest vs. massive
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Questions
• Why are modules everywhere?
• What are they good for?
• Where do they come from?
• What conditions permit or facilitate their emergence?
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Identity
• How are modules recognized by other components of a system?
• Where do module identities come from?
• How can module identity co-evolve with modular architecture?
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Holland’s Tags
• Initially arbitrary identifiers that come to have meaning over time
• Appear to be present in some form in many different kinds of complex adaptive systems
• Examples range from immune systems to armies on a battlefield
• A general tool for the support of emergent complexity
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Evolution of Altruism
• Puzzles/challenges/results since Darwin
• Explanations of altruism toward:
• Kin
• Reciprocating partners
• Agents with good reputations
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Tag-Based Altruism
• Individuals have tags and tag-difference tolerances
• Donate when ∆tags ≤ tolerance
• Riolo et al. (Nature, 2001) showed that tag-based altruism can evolve; Roberts & Sherratt (Nature, 2002) claimed it would not evolve under more realistic conditions
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Spector, L., and Klein, J. Genetic stability and territorial structure facilitate the evolution of tag-mediated altruism. In Artificial Life.
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Evolutionary Computation
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Genetic Programming
• Evolutionary computing to produce executable computer programs.
• Programs are tested by executing them.
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Evolving Modular ProgramsWith “automatically defined functions”
• All programs in the population have the same, pre-specified architecture
• Genetic operators respect that architecture
• Complicated, brittle, limited...
• Architecture-altering operations: more so
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Evolving Modular ProgramsWith “execution stack manipulation”
• Code queued for execution is stored on an “execution stack”
• Allow programs to duplicate and manipulate code that on the stack
• Simple types and uses of modules can be evolved easily
• Does not scale well to large/complex systems
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• Include instructions that tag code (modules)
• Include instructions that recall and execute modules by closest matching tag
• If a single module has been tagged then all tag references will recall modules
• The number of tagged modules can grow incrementally over evolutionary time
Evolving Modular ProgramsWith tags
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Dirt-Sensing, Obstacle-Avoiding Robot Problem
>
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DSOAR Instructions
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DSOAR Effort
8x4 8x6 8x8 8x10 8x12Problem Size
0
2x106
4x106
6x106
8x106
1x107
1.2x107
1.4x107
1.6x107
Com
puta
tiona
l Effo
rt
TagExec
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Evolved DSOAR Architecture (in one environment)
Module0
Module1
3 Module2
1
Module41
Module32 5
Module7
2 2 3
1
Module8
3
2 4
3 8
Module5
3 9
Module6
1 5
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Evolved DSOAR Architecture (in another environment)
Module0
Module2
1
Module9
1
Module10
1
Module11
1
Module121
Module32 8
Module13
1 8
Module14
2 6
Module4
2 7
2 6
Module5
3 8
1 1
1 2
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Conclusions
• Tags provide an effective mechanism for the evolution of modular programs that solve difficult problems
• Tags may provide or explain mechanisms that support the evolution of modularity in a range of other systems, both natural and artificial
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