Altruism A Simulated Investigation COM SCI 194 Honors Research Fall 2007 ~ Spring 2008 Alexander Liu...
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Transcript of Altruism A Simulated Investigation COM SCI 194 Honors Research Fall 2007 ~ Spring 2008 Alexander Liu...
Altruism A Simulated Investigation
COM SCI 194 Honors Research
Fall 2007 ~ Spring 2008
Alexander Liu and Eric Chang
Professor Amit Sahai
Why Study Altruism?
• First, a definition• Existence in species both
animal and human• Impact on human society and
culture• Above all, it’s exciting!
Previous Works
• Haystack model• The evolution of altruism:
Game theory …Fletcher & Zwick
• Usage of A-life to support evolutionary biology theories
• Avida
Mathematical Models• Price’s Equation
“In other words, for b>a there may be a positive contribution to the average altruism as a result of a group growing due to its high number of altruists and this growth can offset in-group losses, especially if the variance of the in-group altruism is low. In order for this effect to be significant, there must be a spread in the average altruism of the groups.”
• Hamilton’s Rule• r = the genetic relatedness • B = the additional reproductive benefit • C = the reproductive cost to the individual of performing the
act.
Our Scope
• Not about morality or conscientious intent…
• Origins and reason for persistence
• How does a gene that decreases the fitness of the individual get passed on through generations?
Approach• Advantages of virtual
simulation• Direct and fast• Building our framework:
eden.java• Design parameters and
requirements• Limitations and caveats
Our Own Little eden (.java)
• Overall description• The world environment• Food availability and
resolution• Reproduction• Genetic variance through
succeeding generations
Base Experiment
• First in our “main line” of experiments
• Either completely altruistic or completely selfish
• Random movement• Results• Why?
Variable Levels
• Altruism levels allowed to vary in increments of 0.1 between 0.0 and 1.0
Variable Altruism, averaged trials
-100
0
100
200
300
400
500
600
700
0 0.2 0.4 0.6 0.8 1 1.2
Sharer
Modifications
Variable Altruism, averaged trials
-100
0
100
200
300
400
500
600
700
0 0.2 0.4 0.6 0.8 1 1.2
Sharer
Sharer/Breeder
Breeder
• Food sharing between parent and child organism
• Same trait governs two behaviors
Genes, not Numbers
Geneset-10, five trials
-50
0
50
100
150
200
250
300
350
400
0 2 4 6 8 10 12
• Instead of a sliding scale, behavior is governed by a gene-set
• Genes have a chance to turn on or off
Extension and Comparison
• Problems with a small gene-set• Effect of increasing the gene-set• Comparison with the previous results
-100
0
100
200
300
400
500
600
700
0 2 4 6 8 10 12
sliding 0-10
geneset- 10 values
geneset- 20 values
Back to the Numbers
0-100
0
50
100
150
200
250
300
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
-100
0
100
200
300
400
500
600
700
800
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
food/breeding
breeding only
• Altruism levels allowed to vary between 0.00 and 1.00 in increments of 0.01
Sexually Determined Altruism
• Regardless of starting conditions, the distribution always converges to a selfish result
Selective Altruism
S elec tive Altruis m
0
20
40
60
80
100
120
1.0:
0.89~0.99:
0.79~0.89:
0.69~0.79:
0.59~0.69:
0.49~0.59:
0.39~0.49:
0.29~0.39:
0.19~0.29:
0.09~0.19:
0.00~0.09:
S electiveA ltruism
• In previous experiments, there is no clear advantage to being altruistic
• Test Condition: altruistic organisms only share with similarly altruistic neighbors
Mutation rate: 20% chance of +- 0.1
Selective Range:
Shares with altruists +- 0.05 range
Altruism vs. Selfishness Revisited
• Hording Behavior Observed • Population Distribution Snapshot at Equilibrium:
Pure Altruistic Pure Selfish
– 1.0: 0 72– 0.9: 0 86– 0.8: 4 79– 0.7: 2 57– 0.6: 15 67– 0.5: 32 41– 0.4: 59 10– 0.3: 87 0– 0.2: 65 1– 0.1: 97 0
• Equilibrium eventually breaks. • Altruists exhibit much more robustness and
consistent rebounding
Conclusions
• Contingent upon several conditions– Conditional altruism– Relatedness and locality
• Beginnings- parent/child interaction
• Persistence– Altruists do benefit (each
other)– Price Equation
Distinctions• Differences between
altruism in animal species and in human society
• The importance of a persistent culture
• And transmission of cultural elements
• Genetic basis versus expression
And…
• Final thoughts
• A big thank you
• Questions?