I must confess that I have something in common with Creationists: I find it difficult to understand how the earliest and simplest life forms came to exist. Unlike the creationists, however, I am not willing to suggest that the earliest life forms were created as-is by some sort of disembodied sentient Supreme Being. I can’t fathom how such a Being could get anything at all done, given that “he” is alleged to be disembodied; for instance, some sort of physical neural network is a prerequisite for cognition. Further, those who posit that life was created as-is by a supernatural Creator need to explain how that Creator got here in the first place; their creation of a Creator constitute an eternal regress. Who created “God,” and God’s God, etc.
Thus, I don’t believe in a ghostly Creator, but where does this leave me? How did the earliest life forms emerge from non-life? Though firm answers have not yet been substantiated through rigorous scientific experimentation, I am intrigued by the ideas put forth by Stuart Kauffman in his 1995 book, At Home in the Universe: The Search for Laws of Self Organization and Complexity.
Early in his book, Kaufman points out that the simplest free living cells (called “pleuromona”) are highly simplified types of bacteria. They have a cell membrane, genes, RNA, protein synthesizing machinery and all the other necessary gear to constitute a form of life. Here’s the problem:
The number of genes pleuromona is variously estimated at a few hundred to about 1000, compared with the estimated 3,000 in Escherichia Coli, a bacterium in our intestines. Pleuromona is the simplest thing we know to be alive. Your curiosity should be aroused. Viruses, which are vastly simpler than the pleuromona, are not free living. They are parasites that invade cells, co-opt the cells metabolic machinery to accomplish their own supper production, escape the host cell, and invade another. All free living cells have at least the minimum molecular diversity of pleuromona. Your antenna should quiver a bit here. Why is there this minimum complexity? Why can’t a system simpler than pleuromona be alive? The best answer that the advocates of the RNA world can offer is an evolutionary just-so story . . . [T]he nude RNA or the nude ribozyme polymerase [stories] offer no deep account of the observed minimum complexity of all free living cells.
Kaufman offers calculations suggesting that it would be well nigh impossible for free-living organizations to evolve based upon the nude RNA theory. It would take too much time because they are too complex to have evolved in the time available for that evolution; there would seem to be a critical mass of complexity inherent in the mechanism of evolvability that would never get off the ground. At this point, it might seem that Kaufman was about to give up on naturalistic explanations and to embrace the reasoning of astronomer Fred Hoyle, described here:
“A junkyard contains all the bits and pieces of a Boeing 747, dismembered and in disarray. A whirlwind happens to blow through the yard. What is the chance that after its passage a fully assembled 747, ready to fly, will be found standing there? So small as to be negligible, even if a tornado were to blow through enough junkyards to fill the whole Universe.” (p.19)
For more on Hoyle’s argument, and how most biologists would respond, see this well-written account.
Kaufman, a theoretical biologist with a focus on complex systems, rejected Hoyle’s concerns. Kauffman argues that Hoyle failed to appreciate “the power of self-organization.” Further,
It is not necessary that a specific set of 2,000 enzymes be assembled, one by one, to carry out a specific set of reactions. . . . There are compelling reasons to believe that whenever a collection of chemicals contains enough different kinds of molecules, a metabolism will crystallize from the broth. If this argument is correct, metabolic networks need not be built one component at a time; they can spring full-grown from a primordial soup. Order for free, I call it. If I am right, the model of life is not We the improbable, but We be expected.
Kauffman is suggesting that once systems reach a critical mass of complexity, the enormous numbers of micro-reactions within will naturally link up to form complex closed loops.
What I call a collectively autocatalytic system is one in which the molecules speed up the very reactions by which they themselves are formed: A makes B; B makes C; C makes A again. Now imagine a whole network of the self-propelling loops … Alone, each molecular species is dead. Jointly, once catalytic closure among them is achieved, the collective system of molecules is alive.
Kaufman argues that life is not limited to template replication, but is “based on a deeper logic.”
I hope to persuade you that life is a natural property of complex chemical systems, that when the number of different kinds of molecules in a chemical soup passes a certain threshold, a self-sustaining network of reactions and autocatalytic metabolism-will suddenly appear. Life emerged, I suggest, not simple, but complex and whole, and has remained complex and whole ever since-not because of a mysterious elan vital, but thanks to the simple profound transformation of dead molecules into an organization by which each molecule’s formation is catalyzed by some other molecule in the organization. The secret of life, the wellspring of reproduction, is not to be found in the beauty of Watson-Crick pairing, but in the achievement of a collective catalytic closure. The roots are deeper than the double helix and are based in chemistry itself. So, in another sense, life–complex, whole, emergent–is simple after all, a natural outgrowth of the world in which we live.
Kaufman argues that the secret lies in the “catalysis” that will occur in open thermodynamic systems. This is a welcome alternative to an equilibrium system, which “corresponds to death.”
Living systems are, instead, open thermodynamic systems persistently displaced from chemical equilibrium. We eat and excrete, as did our remote ancestors. Energy and matter flow through us, building up the complex molecules that are the tokens of the game of life.
Based upon his elegant theoretical models, Kaufman concludes that the emergence of autocatalytic sets is “almost inevitable.” To the extent that he is correct, Kauffman suggests: “Not only are we at home in the universe, but we are far more likely to share it with as yet unknown companions.” Kaufman does not in the least disparage natural selection, but argues that the hidden order offered by self-organization of complex adaptive systems undergirds the capacity to evolve. Nonetheless, he argues that autocatalytic sets “can evolve without a genome,” admitting all-the-while that this is not the kind of evolution we’re used to thinking about.
[A]ll kinds of organic molecules can be substrates and products of reactions, but simultaneously act catalytically to hasten other reactions. No mystery stands in the way of a dual role for chemicals. . . [T]he spontaneous emergence of self-sustaining webs is so natural and robust that it is even deeper than the specific chemistry that happens to exist on earth; it is rooted in mathematics itself.
(Page 59, 61, 69, 71, 73).
Much of Kauffman’s analysis will not come easily to those who have not yet studied complex systems and dynamic systems analyses. Kaufman heavily relies on these tools to the stepladder (rather than the sort of Divine skyhook shunned by Daniel Dennett) that allows natural selection to get off the ground:
One way to get such a network to behave in an orderly manner would be to design it with great care and craft. But we propose that autocatalytic metabolisms arose in the Primal Waters spontaneously, built from a random conglomeration of whatever happened to be around. One would think that such a haphazard concoction of thousands of molecular species would most likely behave in a manner that was disorderly and unstable. In fact, the opposite is true: order arises spontaneously, order for free. . . . To see why order emerges spontaneously I have to introduce some of the concepts mathematicians used to think about dynamical systems . . .
Again, Kaufman’s theoretical models are impressively constructed and described in At Home In the Universe.
When I first encountered Kaufman’s arguments fifteen years ago, his arguments were disorienting to me, but I was eventually sold on the idea of order for free, self organization in non-equilibrium systems (and see here). And further, I am not convinced by the idea of extremely complex critters scaling up from nothing based upon some sort of biological (e.g., DNA) templates.
Some would argue that what Kaufman offers is not true science because it remains too theoretical. Kaufman would be the first to suggest that we have a long way to go to substantiate the manner in which life originated. In the meantime, I would also urge Kauffman doubters to take a careful look at Kauffman’s written work and consider the value his models might offer to future experimentation.
Or, of course, you could simply assert that we don’t know the answer, or you could confidently bellow to your friends and family that you have found all of the answers in ancient religious writings.