The computer model

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Towards the end of the eighteenth century, just as the chemists' critique was giving way, another opposition to mechanism arose and gave origin to a new version of vitalism. This movement started as a spontaneous, almost instinctive, reaction of many biologists to a veritable absurdity that mechanists wanted to impose on biology. It was a revolt against preformationism, the idea that adult structures are already preformed in a homunculus within the fertilised egg. In 1764, Charles Bonnet explicitly launched the great challenge of preformationism: "If organised bodies are not 'preformed', then they must be 'formed' every day, in virtue of the laws of a special mechanics. Now, I beg you to tell me what mechanics will preside over the formation of a brain, a heart, a lung, and so many other organs?"

The challenge was clear, and in order to avoid preformationism biologists were forced to conclude that the formative force required by Bonnet in order to account for embryonic development must indeed exist. It was an embryological, rather than a chemical, force, very close to Aristotle's inner project, but it also was given the name of vis vitalis. Preformationism, as we have seen, was definitely abandoned in 1828, when von Baer's monumental treatise showed that embryonic development is a true epigenesis, as Aristotle had maintained, i.e. a genesis of new structures and not a simple growth of pre-existing structures. Once again, mechanists were forced into admitting that the concept of a "living machine" had to be modified in order to account for the reality of embryonic development, but this time a solution turned out much more difficult to find, and throughout the whole of the nineteenth century the claim of vitalism appeared unsurmountable.

The answer came only with genetics, and more precisely with the discovery that life does not consist only of matter and energy but also of information. In 1909, Wilhelm Johannsen made a sharp distinction between the visible part of any organism (the phenotype) and the part that is carrying hereditary instructions (the genotype), and argued that a living being is not a monad but a dual system, a diarchy, a creature that results from the integration of two complementary realities. Unfortunately, Johannsen's message was either ignored or misunderstood, and it was only the computer, with the distinction of hardware and software, that turned the phenotype-genotype duality into a comprehensible and popular concept.

What matters is that the genotype - the biological software - is a deposit of instructions and therefore is potentially capable of carrying the project of embryonic development. This was the long-awaited answer to vitalism, and the computer became therefore the new model of mechanism. In reality, the new model of a living machine is not the computer that we encounter in our daily life, but an ideal machine known as von Neumann's self-replicating automaton.

John von Neumann, one of the founding fathers of computer science (it was he who invented the central processing unit), asked himself if it is possible to design an automaton that is capable of building any other automaton (a universal constructor), and in particular an automaton that builds copies of itself (a self-replicating machine). His great contribution was the demonstration that such machines are theoretically possible (Figure 1.2). In practice, a von Neumann's self-replicating machine has never been built because of its complexity (it requires more than 200000 components), but the proof that it could be built amounts to saying that it is possible, and proves therefore that a machine is capable of replication (Marchal, 1998). Von Neumann announced these conclusions in 1948, and his work inspired a completely new research field that today is already divided into disciplines and is collectively known as artificial life. A parallel, but different, field is that of artificial intelligence, and it is important to keep them apart. Artificial intelligence studies characteristics that in real life appeared at the end of evolution, whereas artificial life simulates what appeared at the beginning (Sipper, 1998; Tempesti et al, 1998).

In the field of artificial life we are today at a level that organic life reached about 4 billion years ago, at the time of the so-called primordial soup, but the interesting thing is that we could actually witness the origin of this new form of life with our own eyes. This is the last frontier of mechanism, the borderline beyond which the dream could become true.

TM'

UC'

s '

D'(UC+TM )

Figure 1.2 Von Neumann's self-replicating machine.

(A) A universal constructor UC can use its own description D(UC) to build a copy of itself, UC', and of its description D'(UC).

(B) A universal constructor UC can include a universal computer, for example a Turing machine (TM), and build a copy of the entire system from its description D(UC+TM).

Figure 1.2 Von Neumann's self-replicating machine.

(A) A universal constructor UC can use its own description D(UC) to build a copy of itself, UC', and of its description D'(UC).

(B) A universal constructor UC can include a universal computer, for example a Turing machine (TM), and build a copy of the entire system from its description D(UC+TM).

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How to Stay Young

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