Posts Tagged abiogenesis

Abiogenesis

A friendly creationist left a comment on one of the old posts. I thought I’d respond to him or her in more detail here. Here’s what he or she said:

“Am I missing something? This article said nothing about how all life on earth could have evolved in only 4 billions years… NOTHING! But hey, if you want to believe everything arranged itself from a goo or a rock – GO AHEAD!”

That sounds to me like a CHALLENGE!

I certainly don’t believe “everything arranged itself” from a rock, and I’m pretty sure “goo” is only a singular noun in World Of Goo (worth taking a look at)… but I’ll try to explain what I accept as the most likely hypothesis about abiogenesis (which I guess is a synonym for “believe”? eh, close enough).

I’ll also try and simplify it as best I can, but I’m no expert so everyone else can feel free to correct me on this if/when I get it wrong.

Y’see, young earth was a very active place. Volcano’s and meteorites and lots and lots and lots of rain. Imagine the plot of Armageddon combined with the Yellowstone caldera erupting combined with a British Public Holiday, but everywhere.

Anyway, all this activity meant that pretty much every body of water, especially the shallow ones, would have been filled to the brim with volatile chemicals and minerals, like the floor of a chem lab after a shrapnel grenade. And combine a situation like that with an energy source (the sun) and earth would have been home to a whole host of interesting chemical reactions, including those that result in organic compounds.

Note that this isn’t speculation. The famous Urey/Miller experiment might not have been a particularly good simulation of early-earthian conditions, but it demonstrated that if you dump a load of inorganic components together and apply energy, you can get organic compounds easily enough. Besides, it’s successors have done a far better job of simulating early-earthian conditions, with even better results.

But back to early earth. This mix of organic compounds in shallow water, across an entire planet (that’s a lot of space for a microscopic experiment) provides the perfect environment for the formation of more complex chemical reactions, including those involved in abiogenesis.

Now, the exact mechanism of abiogenesis isn’t known, but this isn’t because it’s difficult to make happen. Turns out there’s loads of ways to make a self-replicating molecule. We’re spoiled for choice: there’s so many that it’s hard to pick a “most likely” option. Personally, I like the idea of catalytic cycles.

A catalytic cycle isn’t a self-replicating molecule. A self-replicating molecule is something that builds copies of itself out of whatever molecules exist in it’s environment: so Molecule A takes 2 Molecule B’s and combines them into another Molecule A. A catalytic cycle, on the other hand, is a molecule that builds another molecule, which in turn builds the first molecule. So A builds copies of B, and B builds copies of A. It’s chemical symbiosis, and the component molecules can be even simpler than self-replicating molecules (which are already fairly simple).

Anyway, once you’ve got reproduction, these molecules quickly take over their environment, converting all the “building block” molecules. If one of these cycles changes slightly to use a different mineral to make itself, it will be able to spread further than the original and become dominant where there’s none of the original food. This process can then continue until all the worlds oceans are teeming with catalytic cycles or another variety of chemical self-replicator. From there they become more and more complex, to use more and more ‘food sources’ and fill more and more niches. This is the base for evolution: random mutation + natural selection. It leads to more versatile molecules, to RNA and to DNA, and later to single celled organisms. Since you’re all undoubtedly familiar with evolution, I’ll skip that for now.

As you can see, this process isn’t the creationist misrepresentation of “the components of a cell rolled together by chance”. You might be able to say “the components of a catalytic cycle rolled together by chance”, but that wasn’t so much chance as chemistry.

Of course, the biggest stumbling block for public acceptance of the science behind abiogenesis (well, apart from people desperate to believe the universe as a whole cares about them) is that all this would have happened nearly 4 billions years ago. We don’t even have many *rocks* that old, and even if we did it’s not like molecules fossilize  So there’s no way to know what the exact structure of the early self-replicator/catalytic cycles may have been. Maybe aliens did seed the planet with their dandruff, maybe God did look at a barren rock and think “you know what this needs? SINGLE CELLED ORGANISMS!”, maybe space bacteria from Mars surfed an asteroid here. Maybe all of these things happened at once and God got smacked in the face by an asteroid carrying martian head-lice  We’ll never know for certain. All we can do is try to work out what the most likely scientific hypothesis option is. And that’s abiogenesis.

This isn’t enough for IDists and creationists, though: for some reason (I’ll avoid speculating on motives) they can’t accept that abiogenesis is even a possibility. But since it obviously is (and the research in that area just keeps on confirming this), they need to misrepresent it as something absurd in order to make their arguments from incredulity.

Which brings us back to the comment that sparked this post.

But hey, if you want to believe everything arranged itself from a goo or a rock – GO AHEAD

I don’t want to believe that because it’s a ridiculous misrepresentation. But hey, if you want to believe that the scientific alternative to your own beliefs is blatantly stupid, a fact which has somehow miraculously escaped the attention of every atheist chemist, biochemist and biologist on earth despite them spending their lives researching this stuff… go ahead.

“Or maybe it’s a CONSPIRACY!”

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Abiogenewhat?

Okay, as much as I enjoy telling the development saga, it’s past time for a rant against ignorance. It’s like running for charity, only replace the foot blisters with throat ulcers and the happy children with offended denialists.

Upon what topic of irredeemable stupidity should we feed this rant monster, so it can grow into a big and healthy eldritch abomination whose only desire is to see this world die in internet flame wars? Irreducible complexity? Second law of thermodynamics? Micro vs macro evolution?

No… I’m going to go earlier than that, to a pet hate of mine. The claim: “A cell can’t form by chance.”

From experience, this claim is often accompanied by a bit of good ol’ statistical abuse. The claimant will find a protein, calculate the probability of that protein being that protein, and show off the result as if adding enough to the exponent somehow makes a number important. Here’s a good example from Talk Origins:

”The proteins necessary for life are very complex. The odds of even one simple protein molecule forming by chance are 1 in 10113, and thousands of different proteins are needed to form life.”
Watchtower Bible and Tract Society. 1985. Life–How Did It Get Here? Brooklyn, NY, pg. 44.

Of course, anyone with a basic understanding of statistics and a good pair of heavy boots can kick your ass over this. It’s possible to use the same logic to “prove” that Hydrogen can’t possibly be more common than all the other elements, because each naturally occurring atom only has a 1 in 91 chance of being hydrogen. Besides, the sheer extent of lies upon misinformation upon things-deliberately-overlooked involved in getting these sort of numbers normally indicates the person using them is either a professional charlatan or copy-pasting from the website of a professional charlatan. If you’re interested, check out Lies, Damned Lies, Statistics, and Probability of Abiogenesis Calculations on Talk Origins. I know it’s a little dated, but it’s a fine start. I’ll stay here and deal with the simpler aspect of the claim, using slightly smaller words, not least because I don’t understand all the big ones.

So improbable... not.
(img src: http://www.astrobio.net/pressrelease/83/one-handed-life)

A common answer to the cell-forming-by-chance claim (aside from the fact that the original reproducer is believed to have been far simpler than a modern cell, and was probably little more than a fairly complicated molecule in the right solution to allow it to “reproduce”) is that the forming of the “first cell” has nothing to do with evolution. And that’s perfectly true: this is the domain of abiogenesis, and an acceptance of the still-relatively-young science behind abiogenesis has bugger all to do with accepting the oversized mountains of evidence for evolution. Even if abiogenesis turns out to be a load of rubbish when it comes to explaining the existence of life on earth, evolution remains a highly convincing explanation for the diversity of life on earth.

But that answer is also a cop-out. Abiogenesis is still the most likely method by which life arose on our planet, and as a hypothesis it’s a heck of a lot more complete than the juvenile concept anti-evolutionists so often seem to have of it: namely, that the pieces of a cell “rolled together” purely by chance.

As already stated, the original reproducer was most likely little more than a complicated organic molecule that made copies of itself. Even so, this still sounds like a complex thing to have come about at first, (well, not really: “Self-replicators can be incredibly simple, as simple as a strand of six DNA nucleotides (Sievers and von Kiedrowski 1994)”) until you realise that it didn’t just “come about”: it was the end product of a long chain of natural biochemical reactions, which are far from uncommon. They’re everywhere, reacting with each other and with the results of their own reactions.

Sadly accurate

Given the size of our planet, and the incomprehensible time-frames we’re talking about, is it really so hard to believe that the right sequence of biochemical reactions could result in some sort of imperfect chemical replicator?

Now if you’re a denialist, there’s a good chance you are even now rolling your eyes and saying “it’s all just speculation, he has no evidence”. To which I say: Yes. You’re right, it is speculative. That’s the nature of abiogenesis. We’re talking about microscopic chemical reactions that happened billions of years ago: what “evidence” could we possibly produce aside from a plausible, reproducable path from chemestry to life? We don’t have a TARDIS. But we do have the ability to reason, and sometimes the similarities are striking.

The ‘evidence’ for abiogenesis is that there is life on earth now, and that it wasn’t always there. From these two facts, we can offer plausible explanations, and try to prove them wrong one by one until we’re left with only one option. This is where denialists fail at science. They offer implausible explanations, then try to prove the plausible ones wrong.

I’m not saying there wasn’t a deity who intervened directly and breathed life onto our dead earth 4 billion years ago, or a race of organic engineers who designed the earliest life, or a temporal traveller who accidentally dropped his sandwich in a rock pool. All of these things are possible, in the same way that me being a brain in a jar, or having been created memories-and-all last Thursday, is possible.

But they are not the most likely, plausible, or scientifically supported explanation. That would be Abiogenesis.

/rant
Qu

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“The year is 2033. The last survivors of the Flame War have fled into underground bunkers beneath the shattered remnants of the once great social networking sites. The surface world is given over to unrestricted porn and 4chan mutants. Humanity teeters on the dark brink of extinction.

But we are those who will never give in to despair. We will return to our shattered internet, though it costs us our lives, our very identities. We do not forgive. We do not forget. But we will rebuild.”

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