For Wednesday 16 April Brian Thomas writes: “Fossil Plant Chromosomes Look Modern.”
An 180 million year-old royal fern fossil has been discovered in Sweden that is so stunningly preserved that it still shows the components of individual cells. The nucleus – and even the nucleolus – can be easily seen, and cells that appear to be in the process of division show their chromosomes. The paper, “Fossilized Nuclei and Chromosomes Reveal 180 Million Years of Genomic Stasis in Royal Ferns,” in Science, is unfortunately closed access, but phys.org has pictures. The preservation is good enough, in fact, that the researchers report that they’re basically the same as in living royal ferns. The “living fossil” creationist argument is probably well familiar to you, so the content of Thomas’ article shouldn’t be all that surprising.
The first paragraph of note is the following, specifically the second sentence:
Publishing in the journal Science, three authors from Sweden described the spectacular sub-cellular preservation of a royal fern in Jurassic rock. Mineral-rich water infiltrated its tissues faster than they could even begin to disintegrate.
The fossil has been calcified: this is not a soft tissues story. But Thomas still wants to implicitly make the related claim that the fossil was – and could only have been – produced in the young Earth creationist global flood. This may have something to do why he didn’t mention the the fern was originally buried by a lahar and that, according to the supplementary information, the palynomorphs (pollen, algae etc) found in the deposit were non-marine. As for the minerals, the paper says:
The fern rhizome was permineralized in vivo by calcite from hydrothermal brines that percolated through the coarse-grained sediments shortly after deposition.
This is the result of a catastrophe, sure, but not the one Thomas envisions.
Another piece of trivia in the article is Thomas’ misidentification of a rhizome (the portion of the plant that makes up the fossil) as a “tiny root structure” – he’s thinking of rhizoids, which are more different than their name implies.
But what is his actual argument? That’s largely summed up by the following paragraph:
After 180 million supposed years to work its magic, how could the neo-Darwinian engine of natural selection of beneficial mutations not have made some changes to this fern? Yet the fern remains the same.
This wonderful line sums up the degree to which Thomas doesn’t know what he’s talking about. You see, natural selection isn’t the mechanism that he should be appealing to – better would be genetic drift. It’s important to consider what it actually is that the researchers measured:
Positive scaling relationships rooted in DNA content can be used to extrapolate relative genome sizes and ploidy levels of plants (18–21). We measured minimum and maximum diameters, perimeters, and maximum cross-sectional areas of interphase nuclei in pith and cortical parenchyma cells of the fossil and of its extant relative Osmundastrum cinnamomeum. The measurements match very closely (Fig. 2), with mean nuclear perimeters of 32.2 versus 32.6 μm and mean areas of 82.2 versus 84.9 μm2 in the fossil and in extant Osmundastrum, respectively. The equivalent nuclear sizes demonstrate that the Korsaröd fern fossil and extant Osmundaceae likely share the same chromosome count and DNA content, and thus suggest that neither ploidization events nor notable amounts of gene loss have occurred in the genome of the royal ferns since the Early Jurassic ~180 million years ago [(8), see also discussion in (9, 10)]. These results, in concert with morphological and anatomical evidence (1–6), indicate that the Osmundaceae represents a notable example of evolutionary stasis among plants.
So the size of the nucleus of ancient and modern royal ferns is approximately the same,¹ and so it can be extrapolated that they had roughly the same amount of DNA and number of chromosomes.² This doesn’t even mean that nothing has changed, merely that the net difference is not measurable.
Natural selection is not obliged to change specific genotypes like chromosome number¹ over millions of years. It could, certainly, if that were favourable, but equally it can act to keep them constant. On the other hand the unstoppable processes of mutation and fixation of neutral alleles is a guarantee: the precise sequence of bases in the genome will change quite a bit. The only problem is that the detail we have is not remotely sufficient to be able to compare individual nucleotides.
The argument that Thomas needs to make is that over 180 million years it is inevitable that random genomic turnover should produce measurable differences in DNA quantity. But is it? He cannot even pretend to know, which makes statements like this entirely meaningless:
During this same proposed timespan, some furry little mammal supposedly evolved all the way to people—a fantastic story involving wholesale reorganizations of dozens of fundamentally distinct body forms—while not one chromosome of the royal fern changed at all.
The study authors wrote that this fossil comparison “represents a notable example of evolutionary stasis among plants.” Instead of merely “notable,” perhaps they should have said, “impossible.”
Instead of making an actual point then, Thomas is reduced to semantics:
Plus, isn’t “evolutionary stasis” an oxymoron? Evolution is supposed to mean “constant change,” and “stasis” means “no change.” Something unscientific appears to be going on within a scientist who interprets even a total lack of evolution in an evolutionary way.
“Constant” doesn’t enter into the definition, so far as I know. It’s technically true that you could render the word “evolution” as “change” and so produce an oxymoron, but that has not bearing on evolution as understood scientifically. But since we’re both being needlessly pedantic today, Thomas concludes:
The similarity between a living royal fern and its fossil counterpart plainly presents a problem for millions-of-years. Why do these ferns look so similar? Because their ancestors were ferns that God created only thousands of years ago, according to His own eyewitness testimony.
This is cited to Genesis 1:12, which in the Authorised Version that the ICR uses reads:
And the earth brought forth grass, and herb yielding seed after his kind, and the tree yielding fruit, whose seed was in itself, after his kind: and God saw that it was good.
Ferns are not grasses, nor do they produce seeds, and certainly not fruit. Therefore, God didn’t make them – it makes perfect sense.
TL;DR: Thomas argues that ferns must have changed on the genomic level over 180 million years, but is unable to provide any evidence to support this premise.
- There is a graph in figure 2 that purports to show the relationship between the circumference and diametre of the cell nuclei. Considering the nature of those two properties I’m not sure what they’re trying to prove beyond that the fossilised nuclei are perhaps a little less circular than the modern versions. It reminds me of my year 7 science project, in ways it really shouldn’t.
- The paper talks about “gene content,” but as the paper’s only comment points out this has little relation to the actual quantity of DNA, which is the most they can claim to have measured.
- Ditto phenotypes, like the “morphological and anatomical evidence.”
That was a long break, as seems to have inadvertently become tradition during this time of year. I’ve discovered of late that the length of my commute to and from university is so long that it saps my desire to deal with the stupidity of others, though it leaves me perfectly prepared to be pretty stupid myself. Easter break is imminent, however, and so I may be able to find time to produce some regular, if sparse, content for the rest of the trimester.