1. Empirical Studies of Evolvability in Tierra Preliminary Results
Tom Ray
ATR Kyoto Japan
Zoology, University of Oklahoma

2. Objectives
The objective is to understand how the design and configuration of Tierra-like systems affects the properties of their evolution
The first step is to develop quantitative measures of evolvability

3. Simple Test
Under certain conditions, Tierra tends to evolve towards smaller replicators.
Once a minimal size is reached, evolution stops.
A good index should be able to discriminate the period of evolutionary optimization from the stasis that follows.

4. Evolution and Stasis

5. Period of Stasis origin of dominant genotype
In the run of , genotype 27aal appeared at t=800, and dominated the remainder of the run (until end at t=2500)

6. Origin of 27aal

7. Period of Stasis origin of dominant parasite
At t=1200 a 15 byte parasite entered into an ecologically and evolutionarily stable equilibrium with the 27 byte host

8. Origin of Parasite

9. Viable Mutants
The 27 byte replicator includes three loci at which two instructions are acceptable (8 neutral mutants)
In addition there are viable variants including one-byte insertions or deletions
The 15 byte parasite includes one locus at which two instructions are acceptable and one locus at which any (of 32) instructions are acceptable (64 neutral mutants)

10. Host and Parasite Populations

11. Indices of Evolvability? Based on Genotypes
Number
Turnover: births + deaths of genotypes
Diversity: negative sum of p log p
Integral Sum: all populations over time
Integral Max: largest pop integral over time
Maximum Proportion
Average Age

12. Genotype Number

13. Turnover: births + deaths

14. Diversity: - sum of p log p

15. Maximum Proportion

16. Integral Sum: all populations

17. Integral Max: largest pop integral

18. Integral Max & Max Proportion

19. Integral Sum: all populations

20. Integral Max: largest pop integral

21. Average Age

22. Web Pages
This presentation: evolvability.html
Tierra Home Page:
Tom Ray:

23. The End