Barricelli's numerical organisms were like tropical fish in an aquarium, confined to an ornamental fragment of a foreign ecosystem, sealed behind the glass face of a Williams tube. The perforated cards that provided the only lasting evidence of their existence were lifeless imprints, skeletons preserved for study and display. The numerical organisms consisted of genotype alone and were far, far, simpler than even the most primitive viruses found in living cells (or computer systems) today. Barricelli knew that "something more is needed to understand the formation of organs and properties with a complexity comparable to those of living organisms. No matter how many mutations occur, the numbers... will never become anything more complex than plain numbers."[28] Symbiogenesis--the forging of coalitions leading to higher levels of complexity--was the key to evolutionary success, but success in a closed, artificial universe has only fleeting meaning in our own. Translation into a more tangible phenotype (the interpretation or execution, whether by physical chemistry or other means, of the organism's genetic code) was required to establish a presence in our universe, if Barricelli's numerical symbioorganisms were to become more than laboratory curiosities, here one microsecond and gone the next.

Barricelli wondered "whether it would be possible to select symbioorganisms able to perform a specific task assigned to them. The task may be any operation permitting a measure of the performance reached by the symbioorganisms involved; for example, the task may consist in deciding the moves in a game being played against a human or against another symbioorganism."[29] In a later series of experiments (performed on an IBM 704 computer at the AEC computing laboratory at New York University in 1959 and at Brookhaven National Laboratory in 1960) Barricelli evolved a class of numerical organisms that learned to play a simple but non-trivial game called "Tac-Tix," played on a 6-by-6 board and invented by Piet Hein. The experiment was configured so as to relate game performance to reproductive success. "With present speed, it may take 10,000 generations (about 80 machine hours on the IBM 704...) to reach an average game quality higher than 1," Barricelli estimated, this being the quality expected of a rank human beginner playing for the first few times.[30] In 1963, using the large Atlas computer at Manchester University, this objective was achieved for a short time, but without further improvement, a limitation that Barricelli attributed to "the severe restrictions... concerning the number of instructions and machine time the symbioorganisms were allowed to use."[31]

In contrast to the IAS experiments, in which the numerical symbioorganisms consisted solely of genetic code, the Tac-Tix experiments led to "the formation of non-genetic numerical patterns characteristic for each symbioorganism. Such numerical patterns may present unlimited possibilities for developing structures and organs of any kind to perform the tasks for which they are designed."[32] A numerical phenotype had taken form. This phenotype was interpreted as moves in a board game, via a limited alphabet of machine instructions to which the gene sequence was mapped, just as sequences of nucleotides code for an alphabet of amino acids in translating proteins from DNA. "Perhaps the closest analogy to the protein molecule in our numeric symbioorganisms would be a subroutine which is part of the symbioorganism's game strategy program, and whose instructions, stored in the machine memory, are specified by the numbers of which the symbioorganism is composed," Barricelli explained.[33] In coding for valid instructions at the level of phenotype rather than genotype, evolutionary search is much more likely to lead to meaningful sequences, for the same reason that a meaningful sentence is far more likely to be evolved by choosing words out of a dictionary than by choosing letters out of a hat.

A purely numerical sequence could, in principle (and in time) evolve to be translated, through any number of intermediary languages, into anything else. "Given a chance to act on a set of pawns or toy bricks of some sort the symbioorganisms will 'learn' how to operate them in a way which increases their chance for survival," Barricelli explained. "This tendency to act on any thing which can have importance for survival is the key to the understanding of the formation of complex instruments and organs and the ultimate development of a whole body of somatic or non-genetic structures."[34] Once the concept of translation from genotype to phenotype is given form, Darwinian evolution picks up speed--not just the evolution of organisms, but the evolution of the genetic language and translation system that provide the flexibility and redundancy to survive in a noisy, unpredictable world. A successful interpretive language not only tolerates ambiguity, it takes advantage of it. "It is almost too easy to imagine possible uses for phenotype structures--because the specifications for an effective phenotype is so sloppy," wrote A. G. Cairns-Smith, in his Seven Clues to the Origin of Life . "A phenotype has to make life easier or less dangerous for the genes that (in part) brought it into existence. There are no rules laid down as to how this should be done."[35]

Barricelli's pronouncements had a vaguely foreboding, Butler-ish air about them, despite the disclaimer about confusing "life-like" with "alive." Samuel Butler had warned that Darwin's irresistible logic applied not only to the kingdom of nature but to the kingdom of machines; Nils Barricelli now demonstrated that it was the kingdom of numbers that held the key to that "Great First Cause" of Erasmus Darwin's "one living filament," whether encoded as strings of nucleotides or as strings of electronic bits. Barricelli saw that electronic digital computers heralded an unprecedented change of evolutionary pace, just as Butler had seen evolution quickened by the age of steam.

Barricelli's use of biological terminology to describe self-reproducing code fragments is reminiscent of early pronouncements about artificial intelligence, when machines that processed information with less intelligence than a pocket calculator were referred to as machines that think. A relic from the age of vacuum tubes and giant brains, Barricelli's IAS experiments strike the modern reader as nanve--until you stop and reflect that numerical symbioorganisms have, in less than fifty years, proliferated explosively, deeply infiltrating the workings of life on earth. With our cooperation as symbiotic hosts, self-reproducing numbers are managing (Barricelli would say learning) to exercise increasingly detailed and far-reaching control over the conditions in our universe that are helping to make life more comfortable in theirs. Are the predictions of Samuel Butler and Nils Barricelli turning out to be correct?

"Since computer time and memory still is a limiting factor, the non-genetic patterns of each numeric symbioorganism are constructed only when they are needed and are removed from the memory as soon as they have performed their task," explained Barricelli, describing the Tac-Tix-playing organisms of 1959. He might as well have been describing that class of numerical symbioorganisms --computer software--that we execute and terminate from moment to moment today. "This situation is in some respects comparable to the one which would arise among living beings if the genetic material got into the habit of creating a body or a somatic structure only when a situation arises which requires the performance of a specific task (for instance a fight with another organism), and assuming that the body would be disintegrated as soon as its objective had been fulfilled."[36]

The precursors of symbiogenesis in the von Neumann universe were order codes, conceived (in the Burks-Goldstine-von Neumann reports) before the digital matrix that was to support their existence had even taken physical form. Order codes constituted a fundamental alphabet that diversified in association with the proliferation of different hosts. In time, successful and error-free sequences of order codes formed into subroutines--the elementary units common to all programs, just as a common repertoire of nucleotides is composed into strings of DNA. Subroutines became organized into an expanding hierarchy of languages, which then influenced the computational atmosphere as pervasively as the oxygen released by early microbes influenced the subsequent course of life.