The following chapters illustrate the intricacy of a two-CA system. The model in mind was a host parasite interaction. Soon it became evident that the relationship between the two CA was more intricate. The host developed parasite attributes, and the parasite displayed symbiotic features.
Experiment-1: Two isolated and non interacting CA a grown. Next, CA-1, the parasite encroaches upon CA-2, the host . Soon CA-2 mounts its immune system and kills the parasite.
Experiment-2: Host immunity is inbuilt in the CA structure The experiment investigates, whether the CA state at t = 40 is immunizing. Two CA couples are involved. The first interacts in the same way as in the first experiment. At t = 40 the immune host donates its state to the not immune host of the second couple. Soon after transfer the parasite in the second couple dies, which shows that the host became immune.
Experiment-3: Compare the outcomes of immunity transfer at t = 20 and t = 40. Following both treatment the parasites died, and the hosts became immune. The structure of the two parasites differed. One was somewhat more robust, yet both ultimately died. The outcome of immunization depends on the context of the host. Context is defined as set of processes operating in the organism during immunization.
Experiment-4: Explores the immunizing potential of other states and contexts. State transfers between the two hosts were done at rising times. Not all transfers ended in a successful outcome. In some, CA-1 did not die, in others, CA-2 died. The experiment evaluates only successful outcomes Out of 62 transfers only 16 (=26%) conferred immunity.
Immunization confers more then just immunity. The CA learns new strategies. The different states of the donor CA-2 may be regarded as a library of actions , or a repertory, which may be transferred to the recipient for different purposes. What is the nature of the information transferred from donor to recipient? It is more than a set of signals
Experiment-5: Explores the effect of parasite removal on the system. The parasites were killed at rising times. In 11 instances (=18%) CA-1 killing was followed by CA-2 death. Apparently the relationship between CA-1 and CA-2 involves more than just a one way exploitation. In most cases both CA gained. When CA-2 dies soon after CA-1 is killed it indicates that during their brief encounter CA-2 benefited from a vital substance produced by CA-1. Host responded to parasite killing in three kinds of behavior: Partial dependency on CA—1, Independence and mounting dependence.
The relationship between the two CA involves more than just a one way exploitation. Parasite and symbiont are not as distinct as is commonly viewed. Each host parasite relationship involves also symbiosis.