...oddly enough with a head on both ends

Last night after James and I recorded a fascinating half hour ‘interview’ about his ‘shadow friends’ (more on that another time) we flipped the tape and teamed up on a reading of McElligot’s Pool, one of our favorite Seuss stories. You may remember that it’s a tale told by a boy named Marco about the amazing kinds of fish he might catch in tiny farm pond – if he is patient and cool:

“This might be a pool, like I’ve read of in books,
connected to one of those underground brooks. [...]
This might be a river, now mightn’t it be,
Connecting McElligot’s pool with the sea!”

After first describing a dozen or so other possible quarry, Marco says,

“I might catch an eel....(Well, I might. It depends.)
A long twisting eel with a lot of strange bends,
And oddly enough with a head on both ends!”

Anyway, after James went to bed this two-headed image may have played a germinal role in different cascade of speculation. And after all, my favorite Darwin quote is one he himself had relegated to a box labeled ‘Old and Useless Notes’ – “Without speculation there can be no good and original observation.” So, with that in mind...

This has been a very stimulating week intellectually with several lines of thinking converging and coming into sharper focus. On Monday in our Lib Ed Human Biology course, I lectured about the evolution of our capacity to make choice. Tuesday I made some dissertation headway regarding possible biological foundations of worldview constraints. Wednesday night I talked about current controversies in evolutionary theory (including a brief dismissal of intelligent design) in our freshman Honors. Thursday I got feverishly sick, cancelled my Introductory Genetics class and came home early. As a result, yesterday I attempted to compress two lectures – ‘Eukaryote Gene Expression’ and ‘Genetic Control of Development’ – into one, an admittedly dubious undertaking but hey, the semester is winding down. I ended up focusing on two examples – the effects of light cues on expression of genes crucial to the tick and tocks of biological clocks and the well characterized sequence of developmental events in fruit flies.

So anyway late last night, I went on-line to check a few favorite blogs (Pharyngula, Panda’s Thumb) and found myself following a link to Brainstorms, another pathetic attempt to make Intelligent Design (ID) look like legitimate science. The overall strategy of this site is to identify aspects of nature purportedly inexplicable from a naturalistic perspective and then to assert the necessity of a designer – I was just about to click back to things more interesting when a post entitled “Problems with Characterizing the Protostome-Deuterostome Ancestor” caught my eye. I was pleased (and not surprised!) to find an IDiot defending his empty ideas in response to a cogent critique by Paul Myers at Pharyngula.

A bit of background for non-biologists – bilaterally symmetrical animals like fruit flies, roundworms, mice and (wo)men – are divided into two distinctive groups based on events occurring early in development. As a fertilized egg begins to divide and develop it forms a hollow ball of cells called a blastula; eventually a pocket forms as the blastula folds in on itself at which point we call if a gastrula. Somewhat simplistically, it might help at this point to think of a partially inflated balloon. If you poke a roughly spherical balloon so that it encloses your finger you have the basic shape of a gastrula. Now, in some bilateral animals this first ‘hole’ eventually becomes the mouth. Animals that develop down this path are called protostomes (for ‘mouth first’) and include things like fruit flies and roundworms. In humans and other vertebrates this first opening becomes the exit end of gut and the mouth develops secondarily. Such animals are referred to as deuterostomes. So if protostomes and deuterostomes had a common ancestor (a PDA) some 600 million years ago, did it develop mouth-first or butt-first? (see here for more and backward and upside down relative development). While this poses an as yet unresolved puzzle for a naturalistic evolutionary account of biological diversification, it is hardly the insoluble problem ID advocates seek.

The first step in animal development involves the distinction between the belly and the back of an embryo. This processes is mediated by a transciption factor protein (called dorsal in flies) supplied by the mother and included in the egg. In fruit flies, the second step leads to the development of an anterior-posterior gradient in the developing embryo – this processes depends on maternally derived RNA that are also ‘packed’ with the egg (genes called hunchback and caudal in the case of fruit flies). In the absence of such maternal RNA messages an embryo quite literally wouldn't know its head from its tail – in effect this could be interpreted at a ‘head on both ends’ (or an anus). In any case, it might by useful to think of such a beast as an ambistome (not to be confused with the salamander genus Ambystoma). This possibility becomes more interesting in light of the possibility the that the PDA had a skin-brain; possibly involved in entrainment to light-dark cycles as well as orientation in the water column? Without neural cephalization the 'mouth first vs. anus first' issue almost become moot. Finally, the fact that the all of the above speculation was sparked by perusing an ID web site suggests a possible name for such a hypothetical ambistomic ancestor of protostomes and deuterostomes – Ideous anocephalus!