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| Darwin's "warm little pond" |
"How did life first arise on Earth?" is one of those questions like "What caused the Big Bang?" that creationists and religious apologists love because science either doesn't yet have an answer, or the real answer seems counter-intuitive and thus can be dismissed in front of an audience conditioned to assume that the Universe and everything in it - apart from their assumed god - should be easy to understand and makes intuitive sense even with little or no knowledge of the subject. The answer that the BB was a quantum event and so did not necessarily require a cause, can be waved aside as an evasion rather than an answer. There is never any questioning of the assumptions contained in the question itself.
The question of how life arose, for example, assumes there is some quality or other called 'life' - some almost or actually magical ingredient of living things that makes them living. Ask a creationist to define 'life' and you either get the usual evasion and avoidance or some incoherent gibberish betraying an almost complete ignorance of basic biology, just an assumption that there is something called 'life' which needs explaining. What you never get is a coherent, useable definition of 'life' and yet you are still required to explain in detail and to their complete satisfaction, how it arose.
The questions are obviously designed not to further understanding but to embarrass and discredit science in the belief that "God did it!" then wins by default. And of course any real answers have to be ignored because that conclusion is sacred and immutable. It's all a test of faith, you see.
The fundamental puzzle of the origin of life is not the origin of the hardware, but is the origin of the software.
I have previously proposed that the only real definition of 'life' is in fact localized entropy management - in other words, using energy to reverse the tendency of a system to become more disordered. Biological systems do this by metabolising nutrients as the energy source, derived ultimately either from the sun or, in a few specialised organisms, from geothermal energy. And of course, by replicating, living systems ensure their long-term survival basically by renewing worn out and degenerated parts.Astrobiologist Chris McKay
NASA's Ames Research Center
NASA's Ames Research Center
So this brings me to a paper published yesterday which deals with the mathematical probability of a first replicating molecule arising within a 'sea of molecules' (so many people seem to take Darwin's "warm little pond" for granted when discussing abiogenesis). It was especially pleasing to see Jacob Aaron of New Scientist when discussing this paper to use an almost identical definition to mine with:
One way to define "life" is as a system that fights against the universal increase in entropy, a measure of disorder in systems. All known life has parts that make copies of themselves, and this ability to self-replicate is a way of fighting disorder by maintaining information over time.
Jacob Aaron, Chances of first life improved by weighted dice; New Scientist, 18 September 2014, Magazine issue 2987
The paper by Christoph Adami of Michigan State University, East Lansing, Michigan, USA, uses information theory to show that, if you start with a non-random distribution of monomer molecules, and the distribution is closer to that required to form a replicating molecule, then the probability of spontaneously assembling a chain of monomers with enough information to self-replicate is increased by several orders of magnitude.
Abstract
Research investigating the origins of life usually focuses on exploring possible life-bearing chemistries in the pre-biotic Earth, or else on synthetic approaches. Little work has been done exploring fundamental issues concerning the spontaneous emergence of life using only concepts (such as information and evolution) that are divorced from any particular chemistry. Here, I advocate studying the probability of spontaneous molecular self-replication as a function of the information contained in the replicator, and the environmental conditions that might enable this emergence. I show that (under certain simplifying assumptions) the probability to discover a self-replicator by chance depends exponentially on the rate of formation of the monomers. If the rate at which monomers are formed is somewhat similar to the rate at which they would occur in a self-replicating polymer, the likelihood to discover such a replicator by chance is increased by many orders of magnitude. I document such an increase in searches for a self-replicator within the digital life system avida
You only have to make this very first step, where you are getting some crappy replicator. The moment evolution can actually work with it, you're done.
Christopher Adami
As Jacob Aaron goes on to point out, once a self-replicating molecule has formed, no matter how inefficient, natural selection will take over and improve on it.
I confess I don't know enough about information theory or understand Adami's math well enough to comment on this, other than to say it makes statistical sense that if you load the dice in your favour you improve the probability of getting your desired outcome - that seems a no-brainer to me. However, it begs the question of how the dice got loaded in the first place and Adami mentions one possibility - meteorites, which apparently have a distribution of monomers closer than random to the distribution he thinks was required.
But I have to say this looks a little too convenient an answer and one which I can see playing into the hands of creationist frauds and anti-science ID pseudo-scientists who will inevitably claim scientists have 'proved' that someone had to load the dice for life to be created.
And I wonder if it's necessary anyway. Assuming something like Darwin's "warm little pond", which need not have been that little, we would not be dealing with the analog of dealing a deck of cards, reshuffling, then dealing again until we get that million to one hand; we could be metaphorically dealing tens or hundreds of millions of hands simultaneously over and over again with no aim in mind, incorporating random bits of earlier chains - simply chemistry and physics. It would be just a matter of time for the one in a billion or trillion combination to occur, but, since there was no time limit, the right combination was bound to arise at least once, eventually. After all, if the one in ten million chance didn't happen regularly, no one would ever win the National Lottery.
It might have taken half a billion years for that 'life creating' event to occur, no matter what the monomer distribution was in the pond, and once started we know what happened next.
'via Blog this'
As Jacob Aaron goes on to point out, once a self-replicating molecule has formed, no matter how inefficient, natural selection will take over and improve on it.
ReplyDeleteThe is the critical point -- once the first self-replicating molecule is formed, natural selection takes it from there, regardless of whether the replication process and the things it leads to meet any given definition of "life" or not.
A bunch of atoms spontaneously forming a self-replicating molecule is staggeringly unlikely, perhaps so unlikely that even in a universe of billions of galaxies each containing billions of planets, it might well have happened only once. But given that scale, it's not too implausible that it might have happened once.
Notice that this also explains why we don't see any evidence of other technological civilizations on the universe, something which still mystifies some people.
That and that fact that, for most parts of the Universe or even our own galaxy, even travelling at the speed of light, any information from another civilization would take thousands or millions of years to reach us and travel is for all practical purposes, impossible.
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