Is macroevolution impossible to study (Part 2)?

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The plant kingdom is many things - the basis of agriculture and civilization, a natural laboratory with a stupefying capability in organic synthesis, a source of untold numbers of pharmaceuticals, antimicrobials, herbals, and other chemical playthings, a fascinating range of biological form and function, and an eminently accessible subject for studies of evolution. Along the lines of the last two bullets, one of the more interesting aspects of plants is the range of growth habits that may be adopted. Among these are two sets of contrasting characteristics - annual or perennial, and herbaceous or woody. Differences in these characteristics are among the bases for classification of plant species. For this reason, but also because accompanying morphological differences can be quite considerable, evolutionary changes that involve transitioning between these states are macroevolutionary. Thus, it stands to reason that studying the means by these characteristics evolve amounts to experimental analysis of macroevolution, and understanding the underlying mechanisms constitutes an explanation of macroevolutionary processes.

It is in this light that a recent report deserves some attention. This report, by Melzer et al., describes studies of the functioning of two regulators of flowering in the herbaceous annual Arabidopsis thaliana. These proteins, called SOC1 and FUL, had been known for some time to be involved in the regulation of flowering. Melzer et al. constructed double mutants deficient in the expression of these two proteins, with the intent of understanding the physiological significance of interactions between these two proteins, associations discovered using the so-called yeast two-hybrid assay. Amazingly, soc1 ful double mutants were dramatically different - they had a more woody growth habit, and they behaved like perennials when it comes to reproduction. The abstract from the paper follows this paragraph. The bottom line that is in keeping with the title of the essay - not only can this particular macroevolutionary process be studied experimentally, it can be understood and the corresponding macroevolutionary process recapitulated in a controlled setting.

The abstract:

Plants have evolved annual and perennial life forms as alternative strategies to adapt reproduction and survival to environmental constraints. In isolated situations, such as islands, woody perennials have evolved repeatedly from annual ancestors1. Although the molecular basis of the rapid evolution of insular woodiness is unknown, the molecular difference between perennials and annuals might be rather small, and a change between these life strategies might not require major genetic innovations2, 3. Developmental regulators can strongly affect evolutionary variation4 and genes involved in meristem transitions are good candidates for a switch in growth habit. We found that the MADS box proteins SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and FRUITFULL (FUL) not only control flowering time, but also affect determinacy of all meristems. In addition, downregulation of both proteins established phenotypes common to the lifestyle of perennial plants, suggesting their involvement in the prevention of secondary growth and longevity in annual life forms.

The citation:

Melzer S, Lens F, Gennen J, Vanneste S, Rohde A, Beeckman T. 2008. Flowering-time genes modulate meristem determinacy and growth form in Arabidopsis thaliana. Nature Genetics, published online: 9 November 2008 | doi:10.1038/ng.253

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10 Comments

So, just as in animal evolution, relatively small genetic changes in developmental pathways can have relatively large morphological consequences and these changes can be documented and studied. This once again shows the silliness of any claims that such studies are impossible.

As our understanding of developmental genetics grows, our understanding of macroevolutionary mechanisms grows as well. Only someone completely ignorant of all of this research could make silly claims about it being impossible. If that weren’t bad enough, such individuals often actively try to keep everyone else just as ignorant as they are.

A more accurate generalization would be: there is no evidence that any creationist understands macroevolution.

I’d like to point out two much clearer examples of macroevolution. I’ve seen them discussed on this blog, but nobody seems to appreciate what has happened. These are canine transmissible venereal tumor and Tasmanian devil facial tumor disease.

In both cases, a somatic cell has gone cancerous (nothing unusual here) and become transmissible (unusual, this). Think about this: in a single (or a few) cellular generations, cells from a species have switched from being dead-end passengers in a disposable soma (to be discarded after the gonads do their job) to an independently reproducing unicellular pathogen. I repeat: component of a multicellular organism to independent organism. Mammal to protozoan in one step.

Without genetic analysis, nobody could have said “this infectious cell is actually a dog/devil cell”.

If that’s not a quantum leap, what is?

djlactin said: I’d like to point out two much clearer examples of macroevolution. I’ve seen them discussed on this blog, but nobody seems to appreciate what has happened. These are canine transmissible venereal tumor and Tasmanian devil facial tumor disease.

Yikes - canine transmissible venereal tumor was first described in 1876! Take a look at http://en.wikipedia.org/wiki/Sticker’s_sarcoma

Paul Burnett said: Yikes - canine transmissible venereal tumor was first described in 1876! Take a look at http://en.wikipedia.org/wiki/Sticker’s_sarcoma

Aargh - the comment software makes the link barf - the link actually ends after “sarcoma” - you’ll have to cut-and-paste. Sorry about that.

djlactin: I have several times asked people who deny macroevolution if these examples (and Helacyton) are not adequate. What I really want to know is how these are classified. According to my understanding of the rules of nomenclature, these single-celled organisms should be called mammals, but I gather that so far the issue has been avoided.

What I really want to know is how these are classified.

That question crossed my mind too.

Though as for calling them mammals, the vertebrate classes don’t exactly follow the rules of cladistics, anyway, considering that cladistically speaking, fish includes all five, reptile includes birds, ancient amphibian includes reptile, bird, and mammals, and ancient reptile includes bird and mammal. It’s interesting though that living amphibians are all in a separate clade from reptiles, and living reptiles are separate from mammals.

But as to whether anti-evolutionists would accept any of this, let me guess what one might say:

Well, plants aren’t as important as animals, and they didn’t grow legs or wings, so that’s not really macro.

Those tumor diseases are examples of loss of function, so that’s not really macro, either.

As for referring to those as mammals, well, I could milk that one for another joke, but never mind.

Henry

Sez Henry:

Those tumor diseases are examples of loss of function, so that’s not really macro, either.

Man, if I heard that as an argument, I’d pass an entire cheese sandwich through my nose!

You’d have to get in the speaker’s face and demand: “what about the ‘gain of function’ of becoming an independent pathogen?” (You’d hear the tires squeal.)

Henry J said:

Those tumor diseases are examples of loss of function, so that’s not really macro, either.

That’s when you ask if a four-legged reptile evolving into a legless snake isn’t macroevolution because of a “loss of function.”

“Plants aren’t as imporant as animals” — really? Well – Guess these are people who don’t eat their veggies, build houses, take drugs or breathe. Just saying.….

DS: “Only someone completely ignorant of all of this research could make silly claims about it being impossible.”

In my own defense, as someone completely ignorant of all this research, it’s not just ignorance of the topic; it’s having no way of knowing what relevance a given article has. I can’t imagine someone indulging in free-time perusal of public-access online science journals who would come across this abstract and think, “Eureka! Evidence for macroevolution!” I imagine instead this person would think, “Meristem transitions? Downregulation? Perhaps there’s another article more to my speed.” (After all, for me, it had to be spoon-fed!) Because non-biologists aren’t trained for how to use abstracts.

In short, you are exactly right: ignorance is a big problem. But the problem is harder to solve than you imply. And then there’s the problem of big-name journals which aren’t open to the public, but which contain important papers – not that I’m condemning capitalism; I’m just saying it’s just another roadblock to a well-educated society, which we’ll have to find some way around.

About this Entry

This page contains a single entry by Arthur Hunt published on November 22, 2008 7:32 PM.

Is macroevolution impossible to study? was the previous entry in this blog.

A WTF Moment in Texas: Yup. It was a quote mine. is the next entry in this blog.

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