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Reference Guide

Genetics in Creatures

An Introduction:

© Copyright 1997 CyberLife Technology Ltd. No part of this document may be reproduced without the written permission of CyberLife Technology Ltd. ALL RIGHTS RESERVED. CyberLife is a registered trademark of CyberLife Technology Ltd.

Genetics

The instructions for making living systems are encoded into their DNA (and in the case of viruses, RNA). DNA stands for deoxyribonucleic acid (for RNA, drop the "deoxy" from the beginning), and is made up of chemical instructions for manufacturing proteins—the building blocks of living cells. A complete set of instructions for making one single protein is called a gene.

Collectively, the genetic instructions required to make an entire living system are called the genotype, and the resultant life form is the phenotype.

Genes are joined together in a long string of DNA, punctuated by special markers. This is then wrapped into a giant super-helix called a chromosome. Chromosomes can contain many tens of thousands of genes. Humans carry 46 chromosomes, arranged as pairs—23 from the mother and 23 from the father. They carry a total of around 100,000 genes.

Each cell in the body, with the exception of the sex cells, carry a complete set of chromosome pairs. When egg and sperm cells are manufactured, the chromosomes from the two parents combine to produce a single set in a process called crossing over. The egg and sperm population will therefore contain many unique genomes. During conception, the two single sets of 23 chromosomes combine to produce a new full set of 46. Cells from this full chromosome can then begin to divide normally.

Cells that contain pairs of chromosomes, such as those in humans, are called diploid. Cells containing a single set of chromosomes (such as human sex sperm and egg cells) are called haploid. The chromosomes in Creatures are haploid throughout, so this process functions slightly differently.

Genetics in Creatures

Unfortunately it is beyond the scope of current technology to model this process at the protein level, but the general principle of genetics—a set of instructions describing structures that create systems out of which behaviour can emerge—is borrowed from nature for Creatures.

Creatures genotypes consist of a single haploid chromosome. As a result of being haploid, it has to carry both male and female genes to avoid vital sex genes getting lost during the cross over process. When a creature is created, only the appropriately sexed genes are expressed, those from the other gender are carried but ignored.

The Creatures genetic system has 13 specific gene types, handling biochemistry, brain and creature structure. During successful mating between creatures, the chromosome from each parent is crossed and spliced to produce a new one made up of genes from both donors. To prevent the loss of critical genes, each gene type is preceded by a standard header that indicates which of the crossing over errors are allowed:

  • Duplication. Indicates the gene can be accidentally duplicated
  • Mutation. Individual information pieces within the gene can be mutated
  • Deleted. The gene can be deleted entirely

The standard generation one Norn, as found on the egg disk contains 321 genes of which 12 are female specific and 8 are male specific. As a result of cross-over errors in further generations, the number of genes can vary over time.

Gene Types

  • Sex. Norn D-DNA carries both male and female genes. Some genes can be active for one particular sex only (i.e., the reproductive system), and others are for both (such as the digestive system, immune system, etc.)
  • Mutability. Most genes can be mutated, deleted or duplicated during the breeding process. Some critical genes may not be manipulated in some ways, specified in the mutability box.
  • Switch-on time. This dictates which of the seven life stages at which this gene switches on. To be on at birth, it should be set to "Embryo".

The gene types and their descriptions are shown in the table below. Type and sub-type numbers are shown in brackets after the name:

Gene Type Gene Sub-Type Gene Description
Brain Genes (0) Lobe (0) Defines a brain lobe. (9 in generation 1 creature)

Information stored in this gene includes the amount of neurones and their individual dynamics. This is the most complex gene type—a page by page description is shown after this table

Biochemistry Genes (1) Receptor (0) Chemical receptor. (43 in generation 1 creature)

This binds to a cell in the brain and "fires" when a given chemical reaches a certain threshold. Receptors are used throughout a Creature’s system

  Emitter (1) Chemical emitter. (27 in generation 1 creature)

Binds to a cell in the brain and emits an amount of a specified chemical—the concentration depending on the neurone it is attached to

  Reaction (2) Chemical reaction. (53 in generation 1 creature)

Specifies a chemical reaction and the amounts involved. Chemical reactions are in the form AI + BJ Þ CK + DL, where A, B, C and D are chemical numbers and I, I, K and L are the concentrations involved. All reactions are allowed except nothing Þ something. The reaction rate can also be specified, the approximate half-life of which is shown in the status bar.

  Half Lives (3) Chemical Half-lives. (1 in generation 1 creature)

There is normally only one of these genes, and it specifies the approximate half-life (the time in which it takes a chemical to decay to half its full concentration) for each.

  Initial Concentration (4) Chemical initial concentration. (8 in generation 1 creature)

This gene allows a fixed dose of a chemical to be present when the gene switches on. It is these genes that allow us to give new-born Norns energy (glucose and glycogen) and natural immunity (a low dose of antibodies).

Creature Genes (2) Stimulus (0) Stimulus. (26 in generation 1 creature)

Emit chemicals when a given stimulus occurs. This allows a gene to emit pain when a creature bumps into a wall, for example.

  Genus (1) Species. (1 in generation 1 creature)

The only compulsory gene (although many others are required to make a viable life-form.) This gene specifies the species of creature and the mother and father’s genetic moniker.

  Appearance (2) Graphic appearance ID. (4 in generation 1 creature)

Describes which of the eight possible graphic sets are used to make up any given area of the body. Initially, four are specified: Head, arms, body and legs.

  Pose (3) Creature Pose. (104 in generation 1 creature)

Describes the graphic location information for a Norn to get into any given "pose". There are four walking poses, for example, which are cycled in an animation specified with a "gait" gene (see below).

  Gait (4) Specify pose sequence. (8 in generation 1 creature)

Specifies the poses required to move through a given sequence. For example, there is a gait for normal walking. Different poses switch on at different times to replace these with "older looking" walking sequences as the creature ages.

  Instinct (5) Creature instinct. (19 in generation 1 creature)

Instincts reward creatures for performing a certain action at a certain time. An example instinct is the one that helps creatures to avoid overcrowding. It says that "if the "crowded" drive is high, and I am looking at another creature, and I retreat from it, reward me." After doing this for a while, the creature will learn that retreating from a crowded situation is a good thing

  Pigment (6) Pigmentation. (12 in generation 1 creature)

Refers to a colour and the concentration of that colour. Colours can be red, green or blue.

TOTALS: 13 separate types 321 genes total in generation 1 creature

Female specific genes: 12 (all in the reproductive system)

Male specific genes: 8 (all but one in the reproductive system)

Brain Lobe gene—Detailed gene description:

Page Description of use
General Specifies neurone count, positioning in the brain and all of the common gene parameters such as mutability and switch-on time.
Cell Body Cell body dynamics and cell state rule. State variable rules (or SVRules) dictate how the neurone state is calculated. This is a non-brittle (i.e., mutable) genetically specified expression.
Dendrite 0 growth Class 0 Dendrites – growth, dendrite migration and initial attachment details
Dendrite 0 dynamics Class 0 Dendrites – dynamics.
Dendrite 1 growth Class 1 Dendrites – growth, dendrite migration and initial attachment details
Dendrite 1 dynamics Class 1 Dendrites – dynamics.

You are advised to read the paper "Creatures: Artificial Life Autonomous Software Agents for Home Entertainment." by S. Grand, D. Cliff, A. Malhotra, which was presented at Agents 97. It contains a detailed break-down of how the brain model in Creatures works.

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