Wednesday, 1 May 2019

Perfectly Plausible Abiogenesis

I get more than a little bit bored with almost every debate with creationists eventually, and often very quickly, coming down to a demand that we explain abiogenesis, or more likely an assertion that it can't be explained because it's 'impossible'.

Then comes the parrot squawk, "you can't get life from non-life", as though any of them could define this 'life' thing.

So, with that in mind, I thought I would both give a puff for my book, What Makes You So Special? From the Big Bang to You and put on record a perfectly plausible explanation for how abiogenesis could have happened. Note, it's not meant to be an account of how it actually happened, just how it could have happened, to refute creationist claims that it is impossible.

If any creationists wishes to substantiate that claim, please feel free to go through the following ten steps and say which laws of chemistry and/or physics would make one or more of them impossible. If you can't, clearly, it is not impossible.

This is taken from Chapter 8 - Germinating the Tree of Life. I can't lay claim to the original ten steps which are based on a New Scientist article by Nick Lane and Michael LePage, entitled How life evolved: 10 steps to the first cells although the wording is mine.

Very many of the fundamental internal cell processes that are essential to our lives and the lives of every living thing evolved in bacteria, including maybe the genetic code.

The third thing to understand is that when we talk about a process evolving, we are not talking about something that sprang into existence in a single instance in a single cell. We are usually talking about something that evolved slowly across the entire population, or at least a substantial part of it, with elements of it evolving independently of other elements, then later coming together to form something even more advantageous than the sum of its parts. Even if the probability of an advantageous change occurring are very small, we are talking about bacteria with a generation time often measured in tens of minutes in favourable situations. A hundred million bacteria replicating every hour very quickly produces the billion to one chance.

In addition, bacteria are known to swap genetic material in a simple form of ‘sexual’ reproduction, and they die and leave genetic material around to be taken in by other bacteria. The more successful bacteria will leave more of the good stuff that made them successful lying around in the environment. Then there is the role of viruses. Some viruses insert the DNA version of their RNA into their host’s genome where it can become part of the host’s DNA. So if a virus incorporates the RNA version of an earlier host’s DNA into their own genome, it can be transferred to a new host. The result is that a piece of DNA is now replicated in a new bacterium.

And all the while, generation after generation, natural selection is favouring those better at leaving descendants and quickly removing anything that makes reproduction less likely. Every generation is filtered through a sieve that allows more of the advantageous genes through and fewer of the less advantageous genes, while seriously deleterious genes are quickly eliminated. The effect is to concentrate the advantageous genes up an improbability gradient so what was once the billion to one chance becomes increasingly common in successive generations.

In addition to bacteria, biologists have identified another class of simple, single–celled organisms call archaea. These are similar to bacteria in having a single strand of DNA but they have a different cell membrane enclosing them. Because bacteria and archaea have just a single (circular) strand of DNA they are termed eukaryote cells. Scientists do not yet know for sure whether bacteria evolved from archaea or whether the two different eukaryote cells evolved independently from the first replicating molecules.

The reason this is important to you is that it is here that your oldest genes are being cooked up. Many of the basic processes that make yours and almost everything else’s cells work are being created, not by magic although it is something almost magical, but by the simple process of evolution by natural selection.

Before we skip lightly over the next few billion years to where more complex cells, prokaryote cells, arise we need to go back one step. We need to look at how simple self–replicating molecules became bacteria and archaea.

The honest answer to this question, like the question of how the first simple self–replicating molecule arose and what it was, is that we do not yet know. We do not know if it was a single line of development or two or more that later got together. However, laboratory experiments have come up with a very plausible series of steps, as outlined in a New Scientist article by Nick Lane and Michael Le Page (Lane & Le Page, 2009). They assumed that the most likely location for it to have happened was in porous rocks in alkaline waters around geothermal vents and outlined ten steps:
  1. Water filtering down into newly–formed rocks around geothermal vents reacted with minerals to produce an alkaline, hydrogen and sulphide rich fluid that welled up in the vents.
  2. This fluid reacted with acidic sea water which was then rich in iron to form deposits of highly porous carbonate rock and a foam of iron–sulphur bubbles.
  3. Hydrogen and carbon dioxide trapped in these bubbles reacted to make simple organic molecules such as methane, formates and acetates; reactions that would have been catalysed by iron–sulphur compounds.
  4. The electrochemical gradient between the alkaline fluid in the pores and the acidic seawater would have provided energy to drive the spontaneous formation of acetyl phosphate and pyrophosphate. These behave like ATP (adenosine triphosphate) which powers modern cells. This power supply would in turn power the formation of amino acids and nucleotides.
  5. Currents produced by thermal gradients and diffusion within the porous carbonate rock would have concentrated the larger molecules creating the conditions for building RNA, DNA and proteins and creating the conditions for an evolutionary process where molecules that could catalyse the formation of copies of themselves would quickly dominate and win the struggle for resources.
  6. Fatty molecules would have coated the surface of the pores in the rock, enclosing the self–replicating molecules in a primitive cell membrane.
  7. Eventually, the formation of the protein catalyst, pyrophosphatase enabled the protocell to extract more energy from the acid–alkaline gradient. This enzyme is still found in some bacteria and archaea.
  8. Some protocells would have started using ATP as their primary energy source, especially with the formation of the enzyme ATP synthase. This enzyme is common to all life today.
  9. Protocells in locations where the electrochemical gradient was weak could have generated their own gradient by pumping protons across their membrane using the energy released by the reaction between hydrogen and carbon dioxide, so producing a sufficient gradient to power the formation of ATP.
  10. The ability to generate their own chemical gradient freed these protocells from dependence on the pores in the rock, so they were now free to become free–living cells. This could have happened at least twice with slightly different cells, one type giving rise to bacteria; the other to archaea.
The above ten–step process is of course speculative and probably impossible to test and verify in a laboratory because the conditions around these geothermal vents deep below the ocean would be impossible to replicate in a laboratory, as would the time it might have taken. No–one is claiming it all happened in a day or two, or even weeks or years; not even the lifetime of a working scientist. It could have taken tens or hundreds of millions of years. No–one was in any hurry and there was no objective. Things happened when they happened.

The important point is that none of this is implausible; there is nothing in the laws of chemistry and physics which would prevent it. If chemistry can happen it will happen.

So now we know that the evolution of primitive bacteria–like and archaea–like cells was not only possible but entirely plausible. We do not know the precise details but we know it happened because there are bacteria and archaea around today.

We have now gone from simple, self–replicating molecules to simple eukaryote cells. In a few billion years these will have evolved and refined and perfected their internal chemistry, all the while driven by a simple test of fitness to replicate themselves. Those that were better at it came to dominate those that were not so good, in their particular environment. In a different environment, others came to dominate.


Note again, this is not a claim that this is the precise way that it actually happened and Lane and LePage certainly don't claim it is. It is however, a refutation of the claim that it couldn't have happened.

If a creationist wants to claim that abiogenesis is impossible, they need to refute this ten-step process, otherwise they are knowingly lying.








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1 comment :

  1. Very good bit of writing there.

    I do smile when anyone says "life cannot come from non-life" - if that were true, then it logically follows that life must have pre-existed eternally!

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