Magnetosense

The structure of magnetiteIt’s not quite quantum physics, but in Salmon Use Sophisticated Compass Cells Brian Thomas has another sensory organ he wishes to claim could not have evolved. Curiously, it’s not all that “sophisticated” of one. The PNAS paper he talks about – the Livescience article here – is Magnetic characterization of isolated candidate vertebrate magnetoreceptor cells, which claims to provide a method to detect the presence of magnetically sensitive cells that some animals have been long-suspected of possessing. From the abstract:

In essence, a rotating magnetic field is employed to visually identify, within a dissociated tissue preparation, cells that contain magnetic material by their rotational behavior. As a tissue of choice, we selected trout olfactory epithelium [a type of tissue in the nasal cavity] that has been previously suggested to host candidate magnetoreceptor cells. We were able to reproducibly detect magnetic cells and to determine their magnetic dipole moment. […] The magnetism of the cells is due to a μm-sized intracellular structure of iron-rich crystals, most likely single-domain magnetite. In confocal reflectance imaging, these produce bright reflective spots close to the cell membrane. The magnetic inclusions are found to be firmly coupled to the cell membrane, enabling a direct transduction of mechanical stress produced by magnetic torque acting on the cellular dipole in situ. Our results show that the magnetically identified cells clearly meet the physical requirements for a magnetoreceptor capable of rapidly detecting small changes in the external magnetic field.

Salmon, trout – same thing. For some videos of cells merrily spinning around as part of this experiment, see here.

So, what does Thomas intend to make of this?

How does the salmon find its way from the big, wide ocean to the same stream, hundreds of miles away to the exact same spawning ground of its birth? Studies have shown that the fish use their acute sense of smell to navigate, whereby chemoreceptor cells in their noses detect specific chemicals. Other studies have shown that salmon and other animals somehow also use an internal compass. Researchers have finally discovered it.

Well, children: Sammy Salmon asks Greta GPS for directions… Actually, no, that paragraph seems to be decent. Moving along to something that isn’t:

Further, only one in 10,000 of the fish’s nasal tissue cells were magnetite-containing magnetoreceptors. Senior author of the study, Michael Winklhofer of Ludwig-Maximilians-University in Munich, told Live Science, “If they were as closely packed as photoreceptor cells in the retina or as hair cells in the inner ear, then they would interfere strongly with each other, because their internal compass needles would produce a locally strong magnetic field, which would be felt by the neighboring magnetic cells. Such proximity would deteriorate the magnetic sense.”

The ingenious microscopic compass cells would not even work if they were not distributed as they are among surrounding cells!

No, he didn’t say that.

What he said – and Brian has given us the full quote today, by the way – is that it wouldn’t work as well. That’s not the same thing as the all-or-nothing picture that Thomas is trying to force onto this story. A salmon with a higher concentration of these cells than ideal would still be better off than one with none at all, so natural selection would be more than able to sort things out. We don’t even know anything about the cells arrangement, so far as I can tell, merely that one-in-ten-thousand cells in the nose will rotate under a changing magnetic field.

Continuing:

Would anybody argue that a fully functional compass, complete with a spinning needle, could ever be arranged by accident? Apparently so. University of North Carolina Biologist and expert in animal’s magnetic behaviors [Kenneth Lohmann – ED: the name is strangely ommited from Thomas’ article] told Live Science that since other animals appear to navigate with compass-derived information, then they, too, must have internal compasses similar to salmon. He therefore suggested that additional kinds of magnetoreceptors may have evolved separately.

Thomas seems to be arguing against a different thing than Lohmann’s claim. Lohmann is simply pointing out that given the distribution of magnetism-sensing organisms in the tree of life – not all together, but in disparate places – means that the simplest explanation is that their common ancestor did not have the trait, but that they evolved it separately. Thomas, on the other hand, is arguing that the receptors could not have evolved at all, which is silly. He seems to be imagining some kind of actual compass in the cells, rather than the piece of magnetite that drags the cell around with it. Even humans apparently have magnetite crystals in some of our cells, so the starting position is not even far from the desired outcome. The evolution of this rather simple ‘compass’ would not be difficult.

Thomas concludes:

But there is no evidence for this. It is, as always, an assertion based on a pre-existing commitment to evolution. In fact, the assertion that compasses evolved, which means they constructed themselves piece-by-piece without intelligent input, ignores the fact that the irreducible core compass structure cannot be reduced or amended without destroying its function. The crystals, the cell’s placement, the cell-to-cell sense receptors, and the means to communicate the magnetoreceptor data to the brain for processing must all exist at the same time. And that required a master engineer.

“they constructed themselves piece-by-piece without intelligent input” – that’s a given, really, unless he’s saying that God personally supervised each and every new magnetite crystal cluster being constructed. As for the required elements, all of those would really have been there from the beginning. All that would have been needed, so far as I can see, was for the pre-existing magnetite to be put in a position to put force on the cell membrane. Everything else can be optimised from there. This has got to be one of the worst examples of “irreducible complexity” I’ve seen put forward.

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One thought on “Magnetosense

  1. Physical nature works in mysterious ways!

    But (REAL) empirical science is penetrating those mysterious ways more and more deeply, while “Scientific Creationism” (including its hifalutin semantic equivalent, “[Supernatural] Intelligent Design”) ISN’T!

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