Edge: George Dyson Presentation [page 2]
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DARWIN AMONG THE MACHINES; OR, THE ORIGINS OF [ARTIFICIAL] LIFE?

A Presentation By George Dyson

In examining the prospects for artificial intelligence and artificial life Samuel Butler (1835-1902) faced the same mysteries that permeate these two subjects today. "I first asked myself whether life might not, after all, resolve itself into the complexity of arrangement of an inconceivably intricate mechanism," he recalled in 1880, retracing the development of his ideas. "If, then, men were not really alive after all, but were only machines of so complicated a make that it was less trouble to us to cut the difficulty and say that that kind of mechanism was 'being alive,' why should not machines ultimately become as complicated as we are, or at any rate complicated enough to be called living, and to be indeed as living as it was in the nature of anything at all to be? If it was only a case of their becoming more complicated, we were certainly doing our best to make them so." [1]

These questions can be distilled into one essential puzzle: the origin of life. "We wanted to know whence came that germ or those germs of life which, if Mr. Darwin was right, were once the world's only inhabitants," asked Butler "They could hardly have come hither from some other world; they could not in their wet, cold, slimy state have traveled through the dry ethereal medium which we call space, and yet remained alive. If they traveled slowly, they would die, if fast, they would catch fire."[1] The only viable answer, without recourse to some higher being "at variance with the whole spirit of evolution," was that life "had grown up, in fact, out of the material substances and forces of the world"- as life might once again be growing up out of the material substances and forces of machines.

Freeman J. Dyson, a mathematical physicist better known as one of the architects of quantum electrodynamics, took a mid-career detour into theoretical biology that resulted in a thin volume titled Origins of Life. The essence of my father's hypothesis was that life began not once, but twice. "It is often taken for granted that the origin of life is the same thing as the origin of replication," he wrote, noting "a sharp distinction between replication and reproduction. Cells can reproduce but only molecules can replicate. In modern times, reproduction of cells is always accompanied by replication of molecules, but this need not always have been so. Either life began only once, with the functions of replication and metabolism already present in rudimentary form and linked together from the beginning, or life began twice, with two separate kinds of creatures, one kind capable of metabolism without exact replication, the other kind capable of replication without metabolism.... The most striking fact which we have learned about life as it now exists is the ubiquity of dual structure, the division of every organism into hardware and software components, into protein and nucleic acid. I consider dual structure to be prima facie evidence of dual origin. If we admit that the spontaneous emergence of protein structure and of nucleic acid structure out of molecular chaos are both unlikely, it is easier to imagine two unlikely events occurring separately over a long period of time." [2]

Over a period of twenty years, Dyson developed a toy mathematical model that "allows populations of several thousand molecular units to make the transition from disorder to order with reasonable probability."[3] These self-sustaining--and haphazardly reproducing--autocatalytic systems then provide energy (and information) gradients hospitable to the development of replication, perhaps first of parasites infecting the metabolism of primitive precursors of modern cells. Once metabolism is infected by replication, as the Darwins showed us, natural selection will do the rest.

Natural selection does not require replication; statistically approximate reproduction, for simple creatures, is good enough. The difference between replication (producing an exact copy) and reproduction (producing a similar copy) is the basis of a broad generalization: genes replicate but organisms reproduce. As organisms became more complicated, they discovered how to replicate instructions (genes) that could help them reproduce; looking at it the other way around, as instructions became more complicated, they discovered how to reproduce organisms to help replicate the genes.

If organisms truly replicated, or reproduced even an approximate likeness of themselves without following a distinct set of inherited instructions, we would have Lamarckian evolution, with acquired characteristics transmitted to the offspring. According to the dual-origin hypothesis, natural selection may have operated in a purely statistical fashion for millions if not hundreds of millions of years before self-replicating instructions took control. This brings us back to Butler versus Darwin, because during this extended evolutionary prelude Lamarckian, not neo-Darwinian, selection would have been at work. We should think twice before dismissing Lamarck because Lamarckian evolution may have taken our cells the first - and most significant - step toward where we stand today. Genotype and phenotype may have started out synonymous and only later become estranged by the central dogma of molecular biology that allows communication from genotype to phenotype but not the other way. Life, however, arrives at distinctions by increments and rarely erases its steps. Remnants of Lamarckian evolution may be more prevalent, biologically, than we think - not to mention Lamarckian tendencies among machines.

My father asked three fundamental questions: "Is life one thing or two things? Is there a logical connection between metabolism and replication? Can we imagine metabolic life without replication, or replicative life without metabolism?"[4] These same three questions surround the origin(s) of life among machines. Here, too, a dual-origin hypothesis can shift the balance of probabilities in life's favor once the distinction between reproduction and replication is understood. In looking for signs of artificial life, either on the loose or cooked up in the laboratory, however permeable this distinction may prove to be, one should expect to see signs of metabolism without replication and replication without metabolism first. If we look at the world around us, we see a prolific growth of electronic metabolism, populated by virulently replicating code just as the dual-origin hypothesis predicts. The origins of this go back (at least) to the inauguration of John von Neumann's high-speed electronic digital computer at the Institute for Advanced Study in 1951.

"During the summer of 1951," according to Julian Bigelow, "a team of scientists from Los Alamos came and put a large thermonuclear calculation on the IAS machine; it ran for 24 hours without interruption for a period of about 60 days, many of the intermediate results being checked by duplicate runs, and throughout this period only about half a dozen errors were disclosed. The engineering group split up into teams and was in full-time attendance and ran diagnostic and test routines a few times per day, but had little else to do. So it had come alive."[5]

The age of digital computers dawned over the New Jersey countryside while a series of thermonuclear explosions, led by the MIKE test at Eniwetok Atoll on 1 November 1952, corroborated the numerical results. In 1953, a series of experiments performed at the Institute for Advanced Study demonstrated that digital computers could be used not only to develop the means of destroying life, but to spawn lifelike processes of a form so far entirely unknown.

Italian-Norwegian mathematician Nils Aall Barricelli (1912-1993) arrived at the Institute as a visiting member for the spring term of 1953. Barricelli initiated extensive tests of evolution theories in 1953, 1954, and 1956, using the IAS computer to develop a working model of Darwinian evolution and to investigate the role of symbiogenesis in the origin of life.The theory of symbiogenesis was introduced in 1909 by Russian botanist Konstantin S. Merezhkovsky (1855-1921) and expanded by Boris M. Kozo-Polyansky (1890-1957) in 1924.[6] "So many new facts arose from cytology, biochemistry, and physiology, especially of lower organisms," wrote Merezhkovsky in 1909, "that [in] an attempt once again to raise the curtain on the mysterious origin of organisms... I have decided to undertake... a new theory on the origin of organisms, which, in view of the fact that the phenomenon of symbiosis plays a leading role in it, I propose to name the theory of symbiogenesis."[7] Symbiogenesis offered a controversial adjunct to Darwinism, ascribing the complexity of living organisms to a succession of symbiotic associations between simpler living forms. Lichens, a symbiosis between algae and fungi, sustained life in the otherwise barren Russian north; it was only natural that Russian botanists and cytologists took the lead in symbiosis research. Taking root in Russian scientific literature, Merezhkovsky's ideas were elsewhere either ignored or declared unsound, most prominently by Edmund B. Wilson's dismissal of symbiogenesis as "an entertaining fantasy that the dualism of the cell in respect to nuclear and cytoplasmic substance resulted from the symbiotic association of two types of primordial microorganisms, that were originally distinct."[8]

Merezhkovsky viewed both plant and animal life as the result of a combination of two plasms: mycoplasm, represented by bacteria, fungi, blue-green algae, and cellular organelles; and amoeboplasm, represented by certain "monera without nuclea" that formed the nonnucleated material at the basis of what we now term eukaryotic cells. Merezhkovsky believed that mycoids came first. When they were eaten by later-developing amoeboids they learned to become nuclei rather than lunch. It is equally plausible that amoeboids came first, with mycoids developing as parasites later incorporated symbiotically into their hosts. The theory of two plasms undoubtedly contains a germ of truth whether the details are correct or not. Merezhkovsky's two plasms of biology were mirrored in the IAS experiments by embryonic traces of the two plasms of computer technology -- hardware and software -- that were just beginning to coalesce.


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