Spontaneous combustion! Life is not the same as organized life. Part II.

The idea of spontaneous generation as debated by philosophers before the age of science referred not just to life as a particular kind of self-sustaining chemical reaction, but to that process as manifest in highly organized--differentiated--organisms:  trees, beetles, worms, and all of us.

Maggots--disgusting as they may be--are highly organized forms of life with anatomic structures, highly specialized cells, and that develop by developmental differentiation through sequential patterns of gene expression.  The idea of spontaneous generation referred to such complex creatures, and by extension to all organisms, not just bubbling primal soup.

Even if such soup were to exist today in little cauldrons in the rocks or sea, it would not produce such organisms.  That is the key difference between life as a chemical phenomenon--which it most clearly is--and life as a complex ecology of different organisms, each of which is itself an internal ecology of different organs, which are ecologies of different cell types, and cells have their own internal ecology of subregions, specialized functions, and the like.  This is true even of bacteria, singly and in aggregates, fossils of which have been found from as early as 3.8 billion years ago.  Those don't arise spontaneously!  And that is the very central key to why life is not like crystal formation, volcanoes, and solar systems.  And, of course, it's the deeply insightful awareness of this, by Charles Darwin and at the same time by Alfred Wallace, that we call 'evolution', that was one of the most transforming insights a human being ever had.

Life is about continuation of a reaction--that's, after all, what you are relative to your parents, and their parents, and theirs, and......so on back to the initial lively cauldron.  And more importantly, centrally, life is about the accumulation of divergence of subsets of this reaction.  Divergence requires isolation (we called it partial sequestration in Mermaid's Tale), and transmission with memory (largely resident in DNA) that preserves divergence.  And the way that such divergence with memory accumulates in the kind of life we have here on earth, at least, is brought about by the fact that the basic processes of life are combinatorial and polymeric (see our prior series on this topic).

Genes and the proteins they code for are polymers, long molecules of sequences of a few possible subunits, whose behavior depends on, resides in, and is all about the number, location, and arrangement of particular substrings along the polymer.  That is what accumulates 'information' over time and produces functional subdivision like tissues and organs.

No matter what you may think of maggots (some people actually eat them!), they are marvelously organized, complex forms of life.  New flies are not spontaneously generated; instead, they are just cellular continuations of parent flies.

Any spontaneous generation of new 'living' (biochemical) reactions would simply be simple.  Organization of sequestered substructures and the DNA and protein polymers that make that possible, took hundreds of millions of years, if we can trust the earliest fossil evidence, found by our friend Bill Schopf at UCLA and others.  What we don't allow in modern biological thinking is spontaneous generation of highly organized life.  It must be possible in principle: after all, you and we are just chemical reactions that were generated by the chemical reactions in the eggs that founded us and all the way back to the first soup.  But the probability that a bunch of molecules randomly bouncing around in some puddle in your back yard would generate a bacterial cell, much less a bunny rabbit, is astronomically small (if the universe is truly infinite, however, that must be occurring infinitely many times at this very instant and at every instant--think about that for a while!).

In boring mundane terms, at least, it's not happening here.  Nor are organized structures like, say, bunny ears, being generated out of a tadpole pond.  No, these things are products of very long histories, not short-term instances. 

We need to carry the point forward, because it has fundamental lesson for our view of how evolution works and, generally, is strong support for and reflection of a key point in Darwin's founding theory of evolution.  It's that complex structures arise gradually.  If bunny ears or even just maggots could arise spontaneously, Darwin rightly thought, religious Creationist arguments would be more plausible than historical evolutionary ones.  But the facts show that the evolutionary arguments are the only plausible ones of those that have been offered so far.

Even when complex traits do seem to arise out of nowhere, such as extra vertebrae in the backs of children that were  not present in their parents, this is not spontaneous generation in the usual sense, because these are just anomalous repetitions of processes--like the one that generates vertebrae--that stutter more than usual.

This is why we never find, say, an organ from some dead organism that is totally unlike anything ever seen before.  Nowhere on the tree of the major life-forms that we know of (image grabbed from the Smithsonian Museum's webpage: http://www.mnh.si.edu/exhibits/darwin/treeoflife.html).  Or, less fantastical, we would never unearth a long DNA sequence that was totally unrelated to that of any known type of organism--that could not be shown to fit somewhere in the 'tree' of DNA sequences from plants, animals, and microbes for which we do have sequence.  DNA sequences carry the information for organisms, coding for their traits, and must reflect their history.  

If  we really found a long DNA sequence with no similarity to those we know of, and no structure (such as protein coding elements) that are universal to the life we do know of, we would be in a real quandry: it would be some trick, some product of a  DNA sequencing machine rather than a remnant of actual life, or we would have to rethink our entire theory of the history of life.  It would be very exciting and upsetting--a lot of fun to live through--but there's no sign of it happening.

So this is the deeper sense in which biologists can seriously say that, yes, spontaneous generation did occur once, but no, it is not an explanation for subsequent life.  We're not having our cake and eating it too:  we're saying that a cake takes time to bake!

Spontaneous combustion! How life began, how life begins.... Part I.

How did life begin?  People who don't find the answer in the Bible often believe they'll find it in Darwin's Origin of Species, but of course Darwin doesn't touch on the origin of life at all.  In fact, he doesn't even explain the origin of species.  But that's a story for another day.

For centuries it was viable to speculate that life arose by spontaneous generation. Stuff in the soil, for example, came together to produce organisms.  Of course, the knowledge at that time did not permit definitive study of the question.  But one example was the apparent spontaneous appearance of maggots in dead meat. Ugh!

However,  in 1784 Lazzaro Spallanzani performed a famous experiment (duplicated below by Ken a few years ago, as he described here) that showed these maggots only arose if the meat was exposed to flies, who laid their tiny, unobserved eggs on it.

The maggots did seem to appear spontaneously, but Spallanzani showed that if gauze were placed over the meat, no maggots (Whew!).  Thus, we needed another explanation, and in the age of science another type of spontaneous generation, Creation of species as individual acts of God, wasn't acceptable either.  Now, anyone who argues for spontaneous generation is gently ushered to the psychological services center.  But the story isn't quite so clear cut!

In our book, The Mermaid's Tale, we point out that people no longer believe in spontaneous generation .... except at the beginning, when organic life sprang spontaneously from inorganic elements.  Of course we were not the first to notice this inconsistency.  In fact, Thomas Mann wrote of it much more eloquently 85 years before we did.

In his beautiful book, The Magic Mountain, Mann tells the story of Hans Castorp, a young naval engineer just embarking on his career.  He pays a visit to his cousin in a TB sanatorium, intending to stay for 3 weeks and then return to work, but he ultimately spends 7 years there.  Being set as it is in a place of illness, where both healing and death are integral parts of life, the book is full of musings about the meaning of life, death, time, work, illness, science, art and much more.

Here's Mann on the origins of life (from the John E Woods translation).

What was life?  No one knew.  No one could pinpoint when it had emerged from nature and struck fire.  Nothing in the realm of life was self-actuated or even poorly actuated from that point on.  And yet life seemed to have actuated itself.  If anything could be said about it, then, it was this: life's structure had to be so highly developed that nothing like it could occur in the inanimate world.  The distance between an amoeba--a pseudopod--and a vertebrate was minor, insignificant in comparison to that between the simplest form of life and inorganic nature, which did not even deserve to be called dead--because death was merely the logical negation of life.  Between life and inanimate nature, however, was a yawning abyss, which research sought in vain to bridge.  people endeavored to close that abyss with theories--it swallowed them whole, and was still not an inch less broad or deep.  In the search for some link, scientists had stooped to the absurdity of hypothesizing living material with no structure, unorganized organisms, which if placed in a solution of protein would grow like crystals in a nutrient solution--whereas, in fact, organic differentiation was simultaneously the prerequisite and expression of all life, and no life-form could be proved that did not owe its existence to propagation by a parent.  What jubilation had greeted the first primal slime fished from the sea's deepest deeps--and what humiliation had followed.  It turned out that they had mistaken a precipitate of gypsum for protoplasm.  But to avoid one miracle (because it would be a miracle for life spontaneously to arise out of and return to the same stuff as inorganic matter), scientists had found it necessary to believe in another: archebiosis, that is, the slow formation of organic life from inorganic matter.  And so they went about inventing transitional and intermediate stages, assuming the existence of organisms lower than any known form, but which themselves were the result of even more primal attempts by nature to create life--attempts that no one would ever see, that were submicroscopic in size, and whose hypothesized formation pre supped a previous synthesis of protein. 

Mann goes on to answer the question of what is life poetically, as warmth produced by instability attempting to preserve form, the existence of that with no inherent ability to exist, and so on.  Mann needs no proof to support his answer, he can simply write it and it's there for as long as we can read.

Scientists, though, still struggle with their assumed transitional forms and submicroscopic particles. We claim not to believe in spontaneous generation, but we accept that it occurred (but only once!) in the primordial soup.  That starting event wasn't an act of God, as deists might claim, but the fluke (spontaneous, not pre-ordained) coming together of the right chemicals, perhaps plus some lightning bolts, to start the reaction that we know today as 'life'.

The idea that this occurred only once is preposterous.  It is far more likely that similar conditions in a similar span of time occurred trillions upon trillions of times within and among ponds, tides, shores, seas, rivers, lakes or wherever the magic soup occurred.  What we mean in science is that all of today's life came from one origin.  It leaves its trace of that single start-up.  More on that in a moment.

If we speculate on whether there are little green men (or even little red bacteria) on Mars, as a way of justifying costly tourist adventures there, then that's an acknowledgment that life arose by spontaneous combustion at least twice even within our own solar system!  (Unless of course we believe it was seeded on Earth by a meteor from Mars.) And if, as we discussed in previous posts on life in the universe, there are billions of habitable planets, even just thinking of earth-like life, then spontaneous generation of life is a downright everyday occurrence.  And if one thinks there are nearly infinitely many such planets, spontaneous generation is necessarily occurring somewhere, right this very minute (can you feel it?)!

So, it's not mysticism of any kind to argue for spontaneous generation.  And can we say that it is not still occurring, even here on earth?  One would have to rule out any possibility of the same chemical ingredients being present in right amounts anywhere on earth.  That seems at least somewhat unlikely (though, we think it is widely thought  that the actual origin of life was in an earth with oxygen-free atmosphere, so the question isn't so simple, and perhaps it's not occurring anywhere here any longer).

How can we as scientists deny, much less denigrate, Creationism if we then in our next breath, adopt  Darwin's final metaphor in the Origin, say that life was breathed into an otherwise inanimate earth?  The answer is simple, and relates to what is spontaneously being generated, and to the nature of life not just as a chemical phenomenon, but as a polymer phenomenon, as we described in earlier posts.  In part II of this short series, we'll elaborate.