Contents

• Introduction• Tierra system description• Mac-tierra• Results• Discussion

Introduction

• Exploration of life in general is limited• Tierra is an artificial life model to explore

the origin of diversity

What Is Life?

• “I would consider a system to be living if it is– Self-replicating and– Capable of open-ended evolution

• Synthetic life should self replicate, and evolve structures or processes that were not designed in or preconceived by the creator.”

The Tierra Simulator

• Virtual parallel computer• Cellularity: each program gets its own

memory and CPU time. Each cell can read and execute every instruction but has write permission to its own or its daughter cell

• The operating system executes the code of each cell in the computer’s memory

main memory

instruction codes

cells

operating systemfetch - decode - execute

daughtercell

The Language

• Special machine language to be portable and secure

• Small instruction set (32 instructions, operands included), that is less fragile when the code is mutated

• Jumps: addressing by templates

The Operating System• The slicer: processor time sharing mechanism

– Control time for large/small creatures• The reaper: kills cells when the memory is full

from the top of a queue– The creature starts at the bottom of the queue– It moves up the queue when it fails to execute

instructions (because its algorithm is flawed), and stays where it is, or moves down when it succeeds

• The genebank saves information about each genome

Mutation

• Cosmic mutations cause the flipping of random bits in the soup at a low frequency

• Copy errors result in replication errors• Flaws can occur during execution. The

result is off by 1 at some low frequency• Creatures activity scramble the soup

The Digital Environment: Self-replicating computer programs (colored geometric objects) occupy the RAM memory of the computer (orange background). Mutations (lightning) cause random changes in the code. Death (the skull) eliminates old or defective programs.

Energy

Territory

Abiotic environment

Amino acids

Genome

Natural lifeNatural life

Program

Assembler instructions

Operating system

Memory

CPU time

TierraTierra

The ancestor

• The simulation start with one simple self replicating ancestor - 80 instructions.

• This ancestor evolve communities of interacting “living” creatures, due to mutations.

Ancestor’s Genome01 (nop_1)01 (nop_1)01 (nop_1)01 (nop_1)04 (zero)02 (or1)03 (shl)03 (shl)18 (mov_cd)1c (adrb)00 (nop_0)00 (nop_0)00 (nop_0)00 (nop_0)07 (sub_ac)19 (mov_ab)1d (adrf)00 (nop_0)00 (nop_0)00 (nop_0)

01 (nop_1)08 (inc_a)06 (sub_ab)01 (nop_1)01 (nop_1)00 (nop_0)01 (nop_1)1e (mal)16 (call)00 (nop_0)00 (nop_0)01 (nop_1)01 (nop_1)1f (divide)14 (jmp)00 (nop_0)00 (nop_0)01 (nop_1)00 (nop_0)05 (if_cz)

01 (nop_1)01 (nop_1)00 (nop_0)00 (nop_0)0c (push_ax)0d (push_bx)0e (push_cx)01 (nop_1)00 (nop_0)01 (nop_1)00 (nop_0)1a (mov_iab)0a (dec_c)05 (if_cz)14 (jmp)00 (nop_0)01 (nop_1)00 (nop_0)00 (nop_0)08 (inc_a)

09 (inc_b)14 (jmp)00 (nop_0)01 (nop_1)00 (nop_0)01 (nop_1)05 (if_cz)01 (nop_1)00 (nop_0)01 (nop_1)01 (nop_1)12 (pop_cx)11 (pop_bx)10 (pop_ax)17 (ret)01 (nop_1)01 (nop_1)01 (nop_1)00 (nop_0)05 (if_cz)

self examfind 0000 [start] bxfind 0001 [end] axcalculate size cx

1111

reproduction loopAllocate daughter ax

jump 0010

1101

call 0011 (copy procedure)cell division

copy procedureSave registers to stack

return1110

1100

1010move |bx| |ax|decrement cx

if cx==0 jump 0100increment ax & bxjump 0101

restore registers1011

Ancestor

The Ancestral Program - consists of three “genes” (green solid objects). The CPU (green sphere) is executing code in the first gene, which causes the program to measure itself.

The Parasite

• Uses the ancestor’s copy procedure to copy himself

• The host is not affected by the parasite• Superior competitor • 45 instructions• Population cycles

self examfind 0000 [start] bxfind 0001 [end] axcalculate size cx

1111

reproduction loopAllocate daughter ax

jump 0010

1101

call 0011 (copy procedure)cell division

1110

copy procedureSave registers to stack

return

1100

1010move |bx| |ax|decrement cx

if cx==0 jump 0100increment ax & bxjump 0101

restore registers1011

self examfind 0000 [start] bxfind 0001 [end] axcalculate size cx

1111

reproduction loopAllocate daughter ax

jump 0010

1101

call 0011 (copy procedure)cell division

1110

Ancestor & parasite

A Parasite (blue, two piece object) uses its CPU (blue sphere)to execute the code in the third gene of a neighboring host organism (green) to replicate itself, producing daughter parasite(two-piece wire frame object).

The Hyper-Parasite

• Robust self-replicate program by itself• When a parasite tries to use the hyper-

parasite, the hyper-parasite cause the parasite to replicate the hyper-parasite

• Drive the parasites to extinction

self examfind 0000 [start] bxfind 0001 [end] axcalculate size cx

1111

call 0011

reproduction loopAllocate daughter ax

jump 0000

1101

cell division

1110

copy procedure1100

1010move |bx| |ax|decrement cx

if cx==0 jump 1100increment ax & bxjump 0101

self examfind 0000 [start] bxfind 0001 [end] axcalculate size cx

11111101

reproduction loopAllocate daughter ax

jump 0010

call 0011 (copy procedure)cell division

1110

parasite

Hyper-parasite

A Hyper-parasite (red, three piece object) steals the CPU from a parasite (blue sphere). Using the stolen CPU, and its own CPU (red sphere) it is able to produce two daughters (wire frame objects on left and right) simultaneously.

Symbionts

• Manually created• One contains the self-exam and copy

procedure• The other contains the self-exam and

reproduction loop• 46 and 64 instructions

self examfind 0000 [start] bxfind 0001 [end] axcalculate size cxjump 0010

1111

reproduction loopAllocate daughter ax

jump 0010

1101

call 0011 (copy procedure)cell division

copy procedureSave registers to stack

return1110

1100

1010move |bx| |ax|decrement cx

if cx==0 jump 0100increment ax & bxjump 0101

restore registers1011

symbionts self examfind 0000 [start] bxfind 0001 [end] axcalculate size cxjump 0010

1111

1110

Social Hyper-Parasites

• Appear when there is genetic uniformity• Cooperate with the previous social hyper-

parasite cell• 61 instructions• Jumping templates of size 3

Cheaters: Hyper Hyper Parasites

• Invade the social system• Position themselves between aggregating

hyper parasites to capture the instruction pointer

• 27 instructions

Experiments (Simulations)Hosts, red, are very common. Parasites, yellow, have appeared but are still rare.

Hosts, are now rare because parasites have become very common. Immune hosts, blue, have appeared but are rare.

Immune hosts are increasing in frequency, separating the parasites into the top of memory.

Immune hosts now dominate memory, while parasites and susceptible hosts decline in frequency. The parasites will soon be driven to extinction.

Experiments (Simulations)

• Changing parameters:– Mutation rate– Selection for small/large cells

• Exploring the ecology in controlled environment– Run two competing cells without mutation – Run a fixed population of cells

• Micro/macro scales

Emergence

• Cariani defined emergence relative to the expected model as the state when the model no longer describes the system

• Emergence types:– Syntactic– Semantic– Pragmatic

AL and Biology Theory

BiologyBiology

ALAL

suggest the modelsuggest the factors

experimental studytest biologicaltheories

Biological Factors of Diversity

• Adaptation to biologic evolving environment vs. To physical environment– Emergent fitness function

• Size, shape, distribution, fragmentation, heterogeneity

Possible Extensions

• Predators• Multi-cellular organs• Introducing energy costs• Separating genotype from phenotype

Summary

• A framework for synthesis of life was presented

• Natural-like behavior was detected in the system

• This system opens the way for inter-disciplinary future research

Resources

• The Tierra homepage - Thomas Raywww.hip.atr.co.jp/~ray/tierra/tierra.html

• Mac Tierra - Simon Fraserwww.santfe.edu/~smfr/mactierra.html

• Core life - Erik de Nevewww.xs4all.nl/~alife/corelife.htm