Perusable blogaliciousness for your Friday morning:
The Hairy Museum of Natural History has put out a call for submissions to the Tangled Bank, with an early deadline. If you want a shot at maybe seeing your link with a custom illustration, send it in by Sunday evening. He’ll try to accept stuff up through Tuesday, but make life easy on the guy, OK?
I was reading a review paper that was frustrating because I wanted to know more—it’s on the evolution of complex brains, and briefly summarizes some of the current confusion about what, exactly, is involved in building a brain with complex problem solving ability. It’s not as simple as “size matters”—we have to jigger the formulae a fair bit to take into account brain:body size ratios, for instance, to get humans to come out on top, and maybe bulk is an inaccurate proxy for more significant matters, such as the number of synapses and nerve conduction velocities.
There’s also a growing amount of literature that takes genomic approaches, searching for sequences that show the signatures of selection, and plucking those out for analysis. There have been some provocative results from that kind of work, finding some candidate genes like ASPM, but another of the lessons of that kind of work seems to be that evolution has been working harder on our testis-specific genes than on our brains.
The encouraging part of the paper is that the authors advocate expanding our search for the correlates of intelligence with another group of organisms with a reputation for big brains, but brains that have evolved independently of vertebrates’. You know what I’m talking about: cephalopods!
The Cephalopoda are an ancient group of mollusks originating in the late Cambrian. Ancestors of modern coleoid cephalopods (octopus and squid) diverged from the externally-shelled nautiloids in the Ordovician, with approximately 600 million years of separate evolution between the cephalopod and the vertebrate lineages. The evolution of modern coleoids has been strongly influenced by competition and predatory pressures from fish, to a degree that the behavior of squid and octopus are more akin to that of fast-moving aquatic vertebrates than to other mollusks. Squid and octopuses are agile and active animals with sophisticated sensory and motor capabilities. Their central nervous systems are much larger than those of other mollusks, with the main ganglia fused into a brain that surrounds the esophagus with additional lateral optic lobes. The number of neurons in an adult cephalopod brain can reach 200 million, approximately four orders of magnitude higher than the 20-30,000 neurons found in model mollusks such as Aplysia or Lymnaea. Cephalopods exhibit sophisticated behaviors a number of studies have presented evidence for diverse modes of learning and memory in Octopus and cuttlefish models. This learning capacity is reflected in a sophisticated circuitry of neural networks in the cephalopod nervous system. Moreover, electrophysiological studies have revealed vertebrate-like properties in the cephalopod brain, such as compound field potentials and long-term potentiation. Thus cephalopods exhibit all the attributes of complex nervous systems on the anatomical, cellular, functional and behavioral levels.
Unfortunately, the purpose of the paper is to highlight an unfortunate deficiency in our modern research program: there is no cephalopod genome project. The closest thing to it is an effort to sequence the genome of another mollusc, Aplysia, which is a very good thing—Aplysia is a famous and indispensable subject of much research in learning and memory—but it’s no squid. The authors are advocating additional work on another animal, one with a more elaborate brain.
A parallel effort on a well-studied octopus or squid should provide insights on the evolutionary processes that allowed development of the sophisticated cephalopod nervous system. For example, have cephalopods undergone accelerated evolution in specific nervous system genes, as has been suggested for primates? Have specific gene families undergone expansion in the cephalopod lineage and are these expressed in the nervous system? Are there clear parallels in accelerated evolution, gene family expansion, and other evolutionary processes between cephalopods and vertebrates? Answers to these and related questions will provide useful perspectives for evaluation of the processes thought to be involved in the evolution of the vertebrate brain.
I’m all for it—let’s see a Euprymna genome project!
Jaaro H, Fainzilber M (2006) Building complex brains—missing pieces in an evolutionary puzzle. Brain Behav Evol 68(3):191-195.
The Inoculated Mind twists a Calvin and Hobbes comic to make a point about debates with creationists…I don’t know if I should endorse that kind of tinkering with Holy Writ.
Well, there I am again, mentioned in an article in Nature (Nature Reviews Genetics, actually), but I have to agree with RPM: it’s an awfully thin article that draws unwarranted and hasty conclusions from a tiny sample. It would have been better to actually talk to some of the people blogging about genes and genetics—we tend to be a voluble bunch, I think, and would have given her plenty of material to work with—rather than glancing at a few sites and trying to draw grand generalizations from them.
Skipper M (2006) Would Mendel have been a blogger? Nature Reviews Genetics 7:664.
I’ve been getting swamped with links to this hot article, “Evolution reversed in mice,” including one from my brother (hi, Mike!). It really is excellent and provocative and interesting work from Tvrdik and Capecchi, but the news slant is simply weird—they didn’t take “a mouse back in time,” nor did they “reverse evolution.” They restored the regulatory state of one of the Hox genes to a condition like that found half a billion years ago, and got a viable mouse; it gives us information about the specializations that occurred in these genes after their duplication early in chordate history. I am rather amused at the photos the news stories are all running of a mutant mouse, as if it has become a primeval creature. It’s two similar genes out of a few tens of thousands, operating in a modern mammal! The ancestral state the authors are studying would have been present in a fish in the Cambrian.
I can see where what they’ve actually accomplished is difficult to explain to a readership that doesn’t even know what the Hox genes are. I’ve written an overview of Hox genes previously, so if you want to bone up real quick, go ahead; otherwise, though, I’ll summarize the basics and tell you what the experiment really did.
If you’re at work, I hope you have headphones; if you don’t, check in once you get home. Here are a couple of audio recordings of good science.
Books from Nobel laureates in molecular biology have a tradition of being surprising. James Watson(amzn/b&n/abe/pwll) was catty, gossipy, and amusingly egotistical; Francis Crick(amzn/b&n/abe/pwll) went haring off in all kinds of interesting directions, like a true polymath; and Kary Mullis(amzn/b&n/abe/pwll) was just plain nuts. When I heard that Christiane Nüsslein-Volhard was coming out with a book, my interest and curiousity were definitely piqued. The work by Nüsslein-Volhard and Wieschaus has shaped my entire discipline, so I was eagerly anticipating what her new book, Coming to Life: How Genes Drive Development(amzn/b&n/abe/pwll) would have to say.
It wasn’t what I expected at all, but I think readers here will be appreciative: it’s a primer in developmental biology, written for the layperson! Especially given a few of the responses to my last article, where the jargon seems to have lost some people, this is going to be an invaluable resource.
How do you make a limb? Vertebrate limbs are classic models in organogenesis, and we know a fair bit about the molecular events involved. Limbs are induced at particular boundaries of axial Hox gene expression, and the first recognizable sign of their formation is the appearance of a thickened epithelial bump, the apical ectodermal ridge (AER). The AER is a signaling center that produces, in particular, a set of growth factors such as Fgf4 and Fgf8 that trigger the growth of the underlying tissue, causing the growing limb to protrude. In addition, there’s another signaling center that forms on the posterior side of the growing limb, and which secretes Sonic Hedgehog and defines the polarity of the limb—this center is called the Zone of Polarizing Activity, or ZPA. The activity of these two centers together define two axes of the limb, the proximo-distal and the anterior-posterior. There are other genes involved, of course—this is no simple process—but that’s a very short overview of what’s involved in the early stages of making arms and legs.
Now, gentlemen, examine your torso below the neck. You can probably count five protuberances emerging from it; my description above accounts for four of them. What about that fifth one? (Not to leave the ladies out, of course—you’ve also got the same fifth bump, it’s just not quite as obvious, and it’s usually much more tidily tucked away.)
Carel Brest van Kempen has extracted a few fascinating quotes from an old book he has. It’s titled Creative and Sexual Science, by a phrenologist and physiologist from 1870, and it contains some wonderful old examples of folk genetics.
President Bush would be pleased:
“Human and animal hybrids are denounced most terribly in the Bible; obviously because the mixing up of man with beast, or one beast species with another, deteriorates. Universal amalgamation would be disastrous.”
Although, unfortunately, he then goes on to use this as an argument against miscegenation.
Another lesson is that you shouldn’t deny pregnant women anything, or their longing will mark their child.
“A woman, some months before the birth of her child, longed for strawberries, which she could not obtain. Fearing that this might mark her child, and having heard that it would be marked where she then touched herself, she touched her hip. Before the child was born she predicted that it would have a mark resembling a strawberry, and be found on its hip, all of which proved to be true.”
Don’t let them see horrible things, either.
“Mrs. Lee, of London, Ont., saw Burly executed from her window; who, in swinging off, broke the rope, and fell with his face all black and blue from being choked. This horrid sight caused her to feel awfully; and her son, born three months afterwards, whenever anything occurs to excite his fears, becomes black and blue in the face, an instance of which the Author witnessed.”
And…uh-oh. Maybe George W. Bush won’t be so thrilled with this part.
“A child in Boston bears so striking a resemblance to a monkey, as to be observed by all. Its mother visited a menagerie while pregnant with it, when a monkey jumped on her shoulders.”
I think Carel needs to get busy and transcribe the whole thing onto the web. I know I’ll find these examples useful when I teach genetics this spring.
The science blogosphere must be getting big if it can support biology subspecialty carnivals: now you can read collections of posts about just bioinformatics or genetics. And here I thought a general science carnival might be too narrow to draw in a wide readership, way back in the dark ages!
