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

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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

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500

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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?