Pharyngula

It’s like talking to a brick wall: MacLatchie is appallingly obtuse. When last I argued with him, I pointed out that the major failing of his entire developmental argument against evolution was that it was built on a false premise. As I said then,

I can summarize it with one standard template: “Since Darwinian evolution predicts that development will conserve the evolutionary history of an organism, how do you account for feature X which doesn’t fit that model?” To which I can simply reply, “Evolution does not predict that development will conserve the evolutionary history of an organism, therefore your question is stupid.” It doesn’t matter how many X’s he drags out, given that the premise is false, the whole question is invalid.

So now MacLatchie revisits the debate, and what does he do? He just reiterates his flawed premises!

For those who want the bottom line, here it is. Myers thinks I’m worried about Haeckelian recapitulation. But that’s completely wrong. Neo-Darwinism itself predicts that early development, starting with fertilization, should be conserved.

And then just to make himself look even more stupid, he restates it in simple-minded logical terms.

The logic of my position takes a modus tollendo tollens form of argument:

A

1 If P then Q
2 ~ Q
3 ~ P

By instantiation in A

B

1 If the theory of common descent is true then early developmental stages should be conserved.
2 Early developmental stages are not conserved.
3 The theory of common descent is not true.

The argument is impeccable: Whence the disagreement?

And as if that were not enough, he closes his post by reiterating a variation of the same argument:

C

1 If the theory of common descent is true then mutations to early developmental stages should be beneficial.
2 Early developmental mutations are not beneficial.
3 The theory of common descent is not true.

Good god. After I lectured him about how early developmental stages are not conserved, after I wrote the same thing, after I posted a refutation of his claims by pointing out that his premise is false, he somehow thinks he can win me over by repeating his premises a little more loudly?

Let’s make this equally simple-minded and clear.

Neo-Darwinism does not predict that early development will be conserved.

If it did, since it is trivially observable that there is wide variation in the status of the embryo at fertilization, then neo-Darwinism would be refuted, and would have been falsified prior to its formulation. Yet somehow, people like me, like Pere Alberch who he cited last time and like Rudy Raff who he cites this time, have no problem with evolution while openly discussing the divergence in early embryos.

Think about that, MacLatchie. Isn’t it obvious that you must be missing something?

Here’s another counter-example: Ernst Mayr, about as authoritative a source as you can find on the neo-Darwinian synthesis, wrote a very negative assessment of the likelihood of any molecular homology in the 1960s, before lots of sequence information became available.

Much that has been learned about gene physiology makes it evident that the search for homologous genes is quite futile except in very close relatives (Dobzhansky 1955). If there is only one efficient solution for a certain functional demand, very different gene complexes will come up with the same solution, no matter how different the pathway by which it is achieved (Mayr 1966:609).

Mayr died in 2005, at a time when there was a wealth of comparative information on the ubiquity of conserved genes in development: not only wasn’t conservation of homologous developmental genes a prediction of evolutionary theory, but discovery that there were homologous sequences didn’t induce Mayr to recant evolution on his deathbed.

Is it sinking in yet?

Neo-Darwinism does not predict that early development will be conserved.

It is just freakin’ bizarre to see these guys falling all over themselves to declare that a specific prediction of evolutionary theory has been falsified, when they can’t even comprehend that it is the scientists studying the phenomenon who are handing them all the data that they think invalidates the scientists’ science. The closest thing I can find to it is those crazy creationists who claim that evolutionary theory requires junk DNA, so every time a minor function for any piece of DNA is found, they can claim evolution is refuted.

MacLatchie is hopelessly confused. That early stages should be more resistant to change is not a prediction of evolutionary theory; it’s an inference from molecular genetics, that genes at the base of a long chain of essential interactions ought to be less likely to vary between species. What that doesn’t take into account is that genes are part of the great cloud of environmental interactions that go on to generate a selectable function, and that if the environment in which the gene is expressed changes, it can enable great changes in the activity of the gene.

These early genes are a classic example of this phenomenon: what we see in many lineages is variation in the degree of maternal investment in the egg. It can be yolky, it can be low in yolk, it can have cytoplasmic determinants directly imbedded by maternal factors in the egg, or it can be mostly uniform and regulative. The early zygotic genes can be freed up for evolutionary novelties if their functions are assumed by maternal genes, so we can correlate a lot of this variation with variation in maternal investment.

It wouldn’t be a creationist paper without a quote mine, and MacLatchie does not fail: he quotes Rudolf Raff to support his claims. Rudolf Raff! One of the founders of the whole field of evo-devo! Dragooned into supposedly supporting an Intelligent Design creationism claim! These guys have no shame at all.

Unfortunately, I haven’t read the specific paper MacLatchie cites, but I’m familiar with the work: this is Raff’s beautiful examination of two closely related urchin species, Heliocidaris erythrogramma and H. tuberculata, which are practically indistinguishable in their adult morphology but have radically different embryos. Here’s the abstract, at least, from the paper MacLatchie chose to distort:

Larval forms are highly conserved in evolution, and phylogeneticists have used shared larval features to link disparate phyla. Despite long-term conservation, early development has in some cases evolved radically. Analysis of evolutionary change depends on identification of homologues, and this concept of descent with modification applies to embryo cells and territories as well. Difficulties arise because evolutionary changes in development can obscure homologies. Even more difficult, threshold effects can yield changes in process whereby apparently homologous features can arise from new precursors or pathways. We have observed phenomena of this type in closely related sea urchins that differ in developmental mode. A species developing via a complex feeding larva and its congener, which develops directly, have different embryonic cell lineages and divergent patterns of early development, but converge on the adult sea urchin body plan. Despite differences in embryonic developmental pathways, conserved gene expression territories are evident, as are territories whose homologies are in doubt. The highly derived development of the direct developer evidently arises from an interplay of novel organization of the egg, loss of expression of regulatory gene involved in production of feeding larval features, and changes in site and timing of expression of a number of genes.

I’ve highlighted the relevant part of the story for poor blind MacLatchie. One species is a direct developer: it lays a large yolk-rich egg which develops directly into the round spiky adult form. The other is an indirect developer, which lays a less yolky egg which first forms a feeding ciliated larva which swims about eating before making a metamorphosis into the adult form. These are radically different embryonic forms.

Gosh, I guess evolution is false.

But no! Remember, neo-Darwinism does not predict that early development will be conserved.

The explanation is given right there in Raff’s abstract, which MacLatchie must have read, and equally obviously must not have understood. Raff does, though: he understands that there were evolutionary changes in “novel organization of the egg, loss of expression of regulatory gene involved in production of feeding larval features, and changes in site and timing of expression of a number of genes,” all phenomena entirely compatible with evolutionary theory.

As one last instance of the muddled logic of Jonathan MacLatchie, I will leave you with two quotes from him. The first is from his last article on this subject:

At best, all his case demonstrated was common ancestry — a proposition which is perfectly compatible with intelligent design.

This is a common statement from creationists like Behe, who also say they have no problem with common descent, it’s just that they don’t accept that mutation and selection and natural processes could possibly have done the job. So MacLatchie is just stating the nominal, default, superficial position of many Intelligent Design creationists.

This time around, though, he says this:

If common descent is true, however, early development must somehow evolve via mutations.

Oh, really? Which is it going to be? Does he think common descent is true or not true?

He doesn’t need to answer, I already know it: whichever claim suits his current rhetorical purposes.