Since I recently pointed out the strange news reports of an “octosquid” that even went so far as to call it half squid/half octopus, I thought I’d show why the preliminary assignment to the genus Mastigoteuthis was suggestive. It probably did have 8 arms and 2 tentacles … before it got sucked up in a pipe and flung to the surface. Those two feeding tentacles are delicate.
Figure from Cephalopods: A World Guide (amzn/b&n/abe/pwll), by Mark Norman.
Sometimes, I confess, this whole common descent thing gets in the way and is really annoying. What we’ve learned over the years is that the evolution of life on earth is constrained by historical factors at every turn; every animal bears this wonderfully powerful toolbox of common developmental genes, inherited from pre-Cambrian ancestors, and it’s getting rather predictable that every time you open up some fundamental aspect of developmental pattern formation in a zebrafish, for instance, it is a modified echo of something we also see in a fruit fly. Sometimes you just want to see what evolution would do with a completely different starting point — if you could, as SJ Gould suggested, rewind the tape of life and let it play forward again, and see what novelties arose.
Take the worm. We take the generic worm for granted in biology: it’s a bilaterally symmetric muscular tube with a hydrostatic skeleton which propels itself through a medium with sinuous undulations, and with most of its sense organs concentrated in the forward end. The last common ancestor of all bilaterian animals was a worm, and we can see that ancestry in the organization of most animals today, even when it is obscured by odd little geegaws, like limbs and armor and regional specializations and various dangly spiky jointed bits. You’ll even see the argument made that that worm is the best of all possible simple forms, so it isn’t just an accident of history, it’s a morphological optimum.
But what if we could rewind the tape of life a little bit, to the first worms? Is it possible there are other ways such an animal could have been built? It seems nature may have carried out this little experiment for us, and we have an example of a reinvented worm, one not constructed by common descent from that initial triumphal exemplar in the pre-Cambrian — an alternative worm.
Usually, on my morning walk, I keep my eyes open for any squid that might have washed up on the sidewalks of Morris. Now I learn that the squid wash up on the beaches of Tasmania. I suppose a place nearer an ocean is a more likely spot. (By the way, TONMO is the site to check for more news on the beached squid carcass—and they think it is unlikely that it’s actually a giant squid.)
Maybe I should start scanning for dead baby mammoths, instead.
We now have a draft of the sea anemone genome, and it is revealing tantalizing details of metazoan evolution. The subject is the starlet anemone, Nematostella vectensis, a beautiful little animal that is also an up-and-coming star of developmental biology research.
A most important reason for this work is that the anemone Nematostella is a distant relative of many of the animals that have already been sequenced, and so provides an essential perspective on the evolutionary changes that we observe in those other organisms. Comparison of its genome with that of other metazoans is helping us decipher the likely genetic organization of the last common ancestor of all animals.
A new squid has been caught near Hawaii — much is being made of the fact that it has eight arms instead of ten, but that doesn’t seem like such a big deal to me, since we have the example of Taningia danae with a similar arrangement. It’s more interesting that there is a preliminary assignment to the genus Mastigoteuthis, a curious and poorly understood group of cephalopods.
Jason Rosenhouse has dug into the details of the evo-devo chapter of Behe’s The Edge of Evolution and found some clear examples of dishonest quote-mining (so what else is new, you may be thinking—it’s what creationists do). I’ve warned you all before that when you see an ellipsis in a creationist quote, you ought to just assume that there’s been something cut out that completely contradicts the point the creationist is making; Rosenhouse finds that Behe gets around that little red-flag problem by simply leaving out the ellipses.
I just want to expand a little bit on one point Behe mangles and that Jason quotes. It turns out I actually give a lecture in my developmental biology courses on this very issue, the mathematical modeling antecedents to insect segmentation, so it’s simply weird to see Behe twisting a subject around that is so well understood in the evo-devo community, and that was actually well explained in Sean Carroll’s Endless Forms Most Beautiful.
