Darwin Among the Machines (22 page)

Barricelli enlarged on the theory of cellular symbiogenesis, formulating a more general theory of “symbioorganisms,” defined as any “self-reproducing structure constructed by symbiotic association of several self-reproducing entities of any kind.”
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Extending the concept beyond familiar (terrestrial) and unfamiliar (extraterrestrial) chemistries in which populations of self-reproducing molecules might develop by autocatalytic means, Barricelli applied the same logic to self-reproducing patterns of any nature in space or time—such as might be represented by a subset of the 40,960 bits of information, shifting from microsecond to microsecond within the memory of the new machine at the IAS. “The distinction between an evolution experiment performed by numbers in a computer or by nucleotides in a chemical laboratory is a rather subtle one,” he observed.
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Barricelli saw the IAS computer as a means of introducing self-reproducing structures into an empty universe and observing the results. “The Darwinian idea that evolution takes place by random hereditary changes and selection has from the beginning been handicapped by the fact that no proper test had been found to decide whether such evolution was possible and how it would develop under controlled conditions,” he reported in a review of the experiments performed at the IAS. “A test using living organisms in rapid evolution (viruses or bacteria) would have the serious drawback that the causes of adaptation or evolution would be difficult to state unequivocally, and Lamarckian or other kinds of interpretation would be difficult to exclude. Reproduction plus evolution, however, does not necessarily equal life. In his earliest account of the first round of IAS experiments, submitted to the journal
Methodos
in 1953 and published (in Italian) in 1954, he cautioned his readers that “a question that might embarrass the optimists is the following: ‘If it's that easy to create living organisms, why don't you create a few yourself?'”
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After forty-three years, Barricelli's experiments appear as archaic as Galileo's first attempt at a telescope—less powerful than half a pair of cheap binoculars—although Galileo's salary was doubled by the Venetian Senate in 1609 as a reward. The two Italians compensated for their primitive instruments with vision that was clear. Barricelli tailored his universe to fit within the limited storage capacity of the IAS computer's forty Williams tubes: a total of one two-hundredth of a megabyte, in the units we use today. Operating systems and
programming languages did not yet exist. “People had to essentially program their problems in ‘absolute,'” James Pomerene explained, recalling early programming at the IAS, when every single instruction had to be hand-coded to refer to an absolute memory address. “In other words, you had to come to terms with the machine and the machine had to come to terms with you.”
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Working directly in binary machine instruction code, Barricelli constructed a cyclical universe of 512 cells, each cell occupied by a number (or the absence of a number) encoded by 8 bits. Simple rules that Barricelli referred to as “norms” governed the propagation of numbers (or “genes”), a new generation appearing as if by metamorphosis after the execution of a certain number of cycles by the central arithmetic unit of the machine. These reproduction laws were configured “to make possible the reproduction of a gene only when other different genes are present, thus necessitating symbiosis between different genes.”
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The laws were concise, ordaining only that each number shift to a new location (in the next generation) determined by the location and value of certain genes in the current generation. Genes depended on each other for survival, and cooperation (or parasitism) was rewarded with success. A secondary level of norms (the “mutation rules”) governed what to do when two or more different genes collided in one location, the character of these rules proving to have a marked effect on the evolution of the gene universe as a whole. Barricelli played God, on a very small scale.

The empty universe was inoculated with random numbers generated by drawing playing cards from a shuffled deck. Robust and self-reproducing numerical coalitions (patterns loosely interpreted as “organisms”) managed to evolve. “We have created a class of numbers which are able to reproduce and to undergo hereditary changes,” Barricelli announced. “The conditions for an evolution process according to the principle of Darwin's theory would appear to be present. The numbers which have the greatest survival in the environment . . . will survive. The other numbers will be eliminated little by little. A process of adaptation to the environmental conditions, that is, a process of Darwinian evolution, will take place.”
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Over thousands of generations, Barricelli observed a succession of “biophenomena,” such as successful crossing between parent symbioorganisms and cooperative self-repair of damage when digits were removed at random from an individual organism's genes.

The experiments were plagued by problems associated with more familiar forms of life: parasites, natural disasters, and stagnation when there were no environmental challenges or surviving competitors
against which organisms could exercise their ability to evolve. To control the parasites that infested the initial series of experiments in 1953, Barricelli instituted modified shift norms that prevented parasitic organisms (especially single-gened parasites) from reproducing more than once per generation, thereby closing a loophole through which they had managed to overwhelm more complex organisms and bring evolution to a halt. “Deprived of the advantage of a more rapid reproduction, the most primitive parasites can hardly compete with the more evolved and better organized species . . . and what in other conditions could be a dangerous one-gene parasite may in this region develop into a harmless or useful symbiotic gene.”
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Barricelli discovered that evolutionary progress was achieved not so much through chance mutation as through sex. Gene transfers and crossing between numerical organisms were strongly associated with both adaptive and competitive success. “The majority of the new varieties which have shown the ability to expand are a result of crossing-phenomena and not of mutations, although mutations (especially injurious mutations) have been much more frequent than hereditary changes by crossing in the experiments performed.”
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Echoing the question that Samuel Butler had asked seventy years earlier in
Luck, or Cunning?
Barricelli concluded that “mutation and selection alone, however, proved insufficient to explain evolutionary phenomena.”
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He credited symbiogenesis with accelerating the evolutionary process and saw “sexual reproduction [as] the result of an adaptive improvement of the original ability of the genes to change host organisms and recombine.”
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Symbiogenesis leads to parallel processing of genetic code, both within an individual multicellular organism and across the species as a whole. Given that nature allows a plenitude of processors but a limited amount of time, parallel processing allows a more efficient search for those sequences that move the individual, and the species, ahead.

Efficient search is what intelligence is all about. “Even though biologic evolution is based on random mutations, crossing and selection, it is not a blind trial-and-error process,” explained Barricelli in a later retrospective of his numerical evolution work. “The hereditary material of all individuals composing a species is organized by a rigorous pattern of hereditary rules into a collective intelligence mechanism whose function is to assure maximum speed and efficiency in the solution of all sorts of new problems . . . and the ability to solve problems is the primary element of intelligence which is used in all intelligence tests. . . . Judging by the achievements in the biological world, that is quite intelligent indeed.”
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A century after
On the Origin of Species
pitted Charles Darwin and Thomas Huxley against Bishop Wilberforce, there was still no room for compromise between the trial and error of Darwin's natural selection and the supernatural intelligence of a theological argument from design. Samuel Butler's discredited claims of species-level intelligences—neither the chance success of a blind watchmaker nor the predetermined plan of an all-knowing God—were reintroduced by Barricelli, who claimed to detect faint traces of this intelligence in the behavior of pure, self-reproducing numbers, just as viruses were first detected by biologists examining fluids from which they had filtered out all previously identified living forms.

The evolution of digital symbioorganisms took less time to happen than to describe. “Even in the very limited memory of a high speed computer a large number of symbioorganisms can eirise by chance in a few seconds,” Barricelli reported. “It is only a matter of minutes before all the biophenomena described can be observed.”
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The digital universe had to be delicately adjusted so that evolutionary processes were not immobilized by dead ends. Scattered among the foothills of the evolutionary fitness landscape were local maxima from which “it is impossible to change only one gene without getting weaker organisms.” In a closed universe inhabited by simple organisms, the only escape to higher ground was by exchanging genes with different organisms or by local shifting of the rules. “Only replacements of at least two genes can lead from a relative maximum of fitness to another organism with greater vitality,”
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noted Barricelli, who found that the best solution to these problems (besides the invention of sex) was to build a degree of diversity into the universe itself.

“The Princeton experiments were continued for more than 5,000 generations using universes of 512 numbers,” Barricelli reported. “Moreover, the actual size of the universe was usually increased far beyond 512 numbers by running several parallel experiments with regular interchanging of several (50 to 100) consecutive numbers between two universes. . . . Within a few hundred generations a single primitive variety of symbioorganism invaded the whole universe. After that stage was reached no collisions leading to new mutations occurred and no evolution was possible. The universe had reached a stage of ‘organized homogeneity' which would remain unchanged for any number of following generations. . . . In many instances a new mutation rule would lead to a complete disorganization of the whole universe, apparently due to the death by starvation of a parasite, which in this case was the last surviving organism. . . . Homogeneity problems were eventually overcome by using different mutation rules in different sections of each universe. Also slight modifications of the
reproduction rule were used in different universes to create different types of environment . . . by running several parallel experiments and by exchanging segments between two universes every 200 or 500 generations it was possible to break homogeneity whenever it developed in one of the universes.”
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As Alan Turing had blurred the distinction between intelligence and nonintelligence by means of his universal machine, so Barricelli's numerical symbioorganisms blurred the distinction between living and nonliving things. Barricelli cautioned his audience against “the temptation to attribute to the numerical symbioorganisms a little too many of the properties of living beings,” and warned that “the author takes no responsibility for inferences and interpretations which are not rigorous consequences of the facts presented.”
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He stressed that although numerical symbioorganisms and known terrestrial life-forms exhibited parallels in evolutionary behavior, this did not imply that numerical symbioorganisms were alive. “Are they the beginning of, or some sort of, foreign life forms? Are they only models?” he asked. “They are not models, not any more than living organisms are models. They are a particular class of self-reproducing structures already defined.” As to whether they are living, “it does not make sense to ask whether symbioorganisms are living as long as no clear-cut definition of ‘living' has been given.”
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A clear-cut definition of “living” remains elusive to this day.

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.”
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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.”
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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 nontrivial 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.
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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.”
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