Not Once, but Twice

For his first trick in Discovery Rewrites Plant Evolution, Brian Thomas will dredge up an old botanical discovery from 2009 which he apparently forgot to comment on at the time:

One of the first lessons in plant evolution is that algae existed for millions of years before the more complicated materials and structures necessary to convert them into woody land plants had ever evolved. This lesson sounded more feasible when evolutionists thought that algae were missing a critical land plant tissue-building chemical. But when secular scientists discovered this very material in algae from the coast of California, they invented new lessons to replace the old. Changing evolutionary lessons illustrate important origins lessons.

is that ”one of the first lessons in plant evolution” (I doubt it)? Has Brian ever conceded that any evolutionary process was ‘feasible’? (In this case he would probably have claimed that not having lignin – the chemical in question – was just one more impossible step.) For that matter, is feasibility even affected here? So many questions in this paragraph alone…

And yes, what we think we know about the evolution of life changes sometimes due to new discoveries – that’s because evolution is science.

In 2009, scientists found lignin in the algae Calliarthron. Lignin is an important ingredient because it enables this red alga to resist the wear and tear of living in tumultuous surf. Trees and tall plants use lignin to strengthen their cell walls. It is a complex organic polymer that acts as a glue to stiffen structures, allowing plants to climb high. And the discovery of this lignin in algae turned plant evolution into tumult.

Thomas’ somewhat exaggerated idea of what this finding meant seems to, at least in part, come from the title of the press release that accompanied the paper: Discovery of Land Plant Characteristic in Seaweed May be Evolutionary Curve Ball. Now, I have no cultural reference point when it comes to baseball metaphors, but as I understand it a “curve ball” would be considered a bad thing. The other main aspect is that Brian likes to confuse challenges to a specific evolutionary narrative with a challenge for evolution itself – we very much have the former here.

Current Biology. They expressed difficulty believing that plants’ abilities to manufacture lignin evolved two times—once in algae and once in land plants. The study authors wrote, “Because monolignol [lignin chemical] synthesis is exceptionally complex, it seems unlikely that Calliarthron and terrestrial plants evolved monolignol biosynthesis and polymerization completely independently.”

But why should this be difficult for an evolutionist to believe? If evolution is powerful enough to produce people, pine trees, and pangolins from primordial protists, then what would hinder it from inventing lignin multiple times?

Professor Mark Denny told the University of British Columbia, “The pathways, enzymes and genes that go into making this stuff are pretty complicated, so to come up with all those separately would be really, really amazing. Anything is possible, but that would be one hell of a coincidence.”

The title of the paper was Discovery of lignin in seaweed reveals convergent evolution of cell-wall architecture, but Professor Denny, a co-author, is here (in a quote from the aforementioned press release) expressing a degree of scepticism over whether it is indeed convergent evolution that has occurred. I’m not actually sure why this is justified.

If it is difficult to believe that lignin production evolved twice, then it should be difficult to believe that it evolved even once.

What Thomas either does not understand or does not wish to explain to his readers is why that line is false. There will often be many possible ways that a given outcome can be brought about – involving different enzymes and different metabolic pathways – and none of them need be difficult for evolution to bring to reality. Whichever one is favoured will, to a significant degree, come down to chance. However the chances of a second, entirely independent lineage producing the same solution – assuming they are all equal, of course – are rather low, and it’s this that Denny seems to have been talking about. In the light of that information Thomas’ conclusion does not logically follow – the chances of a second roll of a die producing the same number as the first is low, but the chances of the first roll producing any number at all need not be.

The reason why I’m not sure why the ‘one hell of a coincidence’ needs to be invoked here comes from the following line in the papers abstract:

Although “lignin-like” compounds have been identified in primitive green algae, the presence of true lignins in nonvascular organisms, such as aquatic algae, has not been confirmed.

So we already have similar compounds known – could it be that plants were already irreversibly on the path to the use of lignin anyway? That would reduce the odds significantly. If the conclusion to the press release is correct, the first author of the paper, Dr Patrick Martone, set off to solve the question of whether this is convergent evolution or not:

Martone says the research team has started looking for billion-year-old lignin genes that might be shared among land plants and red algae, and has started exploring whether lignin exists in other aquatic algae and what role it plays in the evolution and function of aquatic plants.

Looking at these things should allow him to differentiate between convergent evolution – where the common ancestor of both land plants and algae did not have the trait and separately evolved it – and the possibility that the common ancestor did have it but it has been lost or not used in most algae.

Arbuscular mycorrhiza in flax roots under a microscopeFor his second trick, Brian expresses his ignorance of how symbiosis evolves:

And according to more recent plant evolution news, land plants needed another lucky coincidence to have evolved. Certain bacteria and fungi are specifically suited to have biochemical dialogues with plant root cells to collaborate on obtaining and converting nitrogen from the atmosphere to a biologically useful form. They even share gene segments for a critical enzyme. The fungus genome has half of the gene, and the plant genome has the other half.

Could this, too, have come from a lucky coincidence?

Ironically, while he claims that this ‘news’ is newer he is in fact just using template I used to call ‘type Io’ – using a new discovery or study as an excuse to talk about something already known that he could have written an article about at any time in the past. The symbiosis here is known as arbuscular mycorrhiza, while the new paper is Contrasting arbuscular mycorrhizal responses of vascular and non-vascular plants to a simulated Palaeozoic CO2 decline (which doesn’t seem to even mention the enzyme).

One way – just one – that you could evolve a relationship such as the one described would involve starting with two enzymes, one from the fungus and one from the plant. These enzymes can interact, and in a way beneficial to both sides. We’ll also say that an increase in the interaction between the enzymes is also beneficial. Over time the enzymes get more and more involved with each other (because, as I said, that is beneficial in this case), and both organisms increasingly come to rely on this fact. The inevitable consequence of a few billion years of this that the two enzymes become literally inseparable, even though the code for their manufacture is split between different species – the outcome is really no different than if the genes were in the same organism. The “lucky coincidence” that Thomas seems to be implying is that the two genes were randomly created in the final form, but this is in no way necessary or at all likely.

The conclusion to Thomas’ article is:

Any suggestion of nature creating lignin manufacturing facilities, or of nature “creating the wonderfully varied terrestrial ecosystems” that contain over 173 different plant families, is “really, really amazing”—too amazing to be true. One lesson emerges from this. Because nature could not have made lignin twice or even once, and because nature could not have made plants, something outside nature must have.

Very, very little of that is true.

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One thought on “Not Once, but Twice

  1. “Looking at these things should allow him to differentiate between convergent evolution – where the common ancestor of both land plants and algae did not have the trait and separately evolved it – and the possibility that the common ancestor did have it but it has been lost or not used in most algae.”

    The Abstract to the paper mentioned at footnote 2 states: “The finding of secondary walls and lignin in red algae raises many questions about the convergent or deeply conserved evolutionary history of these traits, given that red algae and vascular plants probably diverged more than 1 billion years ago”.
    http://www.ncbi.nlm.nih.gov/pubmed/19167225

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