Pharyngula
Evolution, development, and random biological ejaculations from a godless liberal
I made a mistake that was quickly corrected by a correspondent. Yesterday, in writing about copy number variants in human genes, I used the example of the amylase gene on chromosome 1, which exists in variable numbers of copies in human populations, and my offhand remark was that the effect is “nothing that we can detect”, but that maybe people with extra copies would be “especially good at breaking down french fries”. Well, it turns out that we can detect this, that there was even a very cool study of this enzyme published last year, and that the ability to break down complex starches rapidly may have been a significant factor in human evolution.
So of course I have to tell you all about this now.
The Institute for Creation Research has a charming little magazine called “Acts & Facts” that prints examples of their “research” — which usually means misreading some scientific paper and distorting it to make a fallacious case for a literal interpretation of the bible. Here’s a classic example: Chimps and People Show ‘Architectural’ Genetic Design, by Brian Thomas, M.S. (Note: this is not the peer-reviewed research paper implied by the logo to the left — that comes later.) The paper is a weird gloss on recent work on CNVs, or copy number variants. Mr Thomas makes a standard creationist inference that I have to hold up for public ridicule.
Here’s an interesting example of genetic programming: use a program that slightly alters colored polygons, compares the results to a target, and selects variants that most resemble the Mona Lisa. After less than a million generations, a black square turned into this:
Not bad. The description of the algorithm is a bit thin, but he promises to release the source code soon. It sounds like a million generations is an overestimate, since his population size in each generation was 1, and it also sounds like his selection was far more stringent than you’d find in nature, but it’s an interesting if oversimplified example of the power of chance and selection.
Simon Ings has written a wonderful survey of the eye, called A Natural History of Seeing: The Art and Science of Vision(amzn/b&n/abe/pwll), and it’s another of those books you ought to be sticking on your Christmas lists right now. The title give you an idea of its content. It’s a “natural history”, so don’t expect some dry exposition on deep details, but instead look forward to a light and readable exploration of the many facets of vision.
There is a discussion of the evolution of eyes, of course, but the topics are wide-ranging — Ings covers optics, chemistry, physiology, optical illusions, decapitated heads, Edgar Rice Burroughs’ many-legged, compound-eyed apts, pointillisme, cephalopods (how could he not?), scurvy, phacopids, Purkinje shifts…you get the idea. It’s a hodge-podge, a little bit of everything, a fascinating cabinet of curiousities where every door opened reveals some peculiar variant of an eye.
Don’t think it’s lacking in science, though, or is entirely superficial. This is a book that asks the good questions: how do we know what we know? Each topic is addressed by digging deep to see how scientists came to their conclusion, and often that means we get an entertaining story from history or philosophy or the lab. Explaining the evolution of our theories of vision, for example, leads to the story of Abu’Ali al-Hasan ibn al-Hasan ibn al-Haythem, who pretended to be mad to avoid the cruelty of a despotic Caliph, and who spent 12 years in a darkened house doing experiments in optics (perhaps calling him “mad” really wasn’t much of a stretch), and emerged at the death of the tyrant with an understanding of refraction and a good theory of optics that involved light, instead of mysterious vision rays emerging from an eye. Ings is also a novelist, and it shows — these are stories that inform and lead to a deeper understanding.
If the book has any shortcoming, though, it is that some subjects are barely touched upon. Signal transduction and molecular evolution are given short shrift, for example, but then, if every sub-discipline were given the depth given to basic optics, this book would be unmanageably immense. Enjoy it for what it is: a literate exploration of the major questions people have asked about eyes and vision for the last few thousand years.
Last week’s Friday Cephalopod actually has an interesting story behind it. It was taken from a paper that describes the evolutionary radiation of deep-sea cephalopods.
First, a little background in geological history. Antarctica is a special case, in which a major shift in its climate occurred in the last 50 million years. If you look at a map, you’ll notice that Antarctica comes very close to the southern tip of South America; 50 million years ago, they were fully connected, and they only separated relatively recently due to continental drift.
The Atlantic has republished Asa Gray’s review of Darwin’s Origin from 1860. It’s a fascinating read: Asa Gray was a general supporter of Darwin, and the two of them corresponded regularly, and the review is generally positive, pointing out the power of the evidence and the idea. However, Gray is also quite plain about the way the implications of the theory make him very uncomfortable, and you can see him casting about, looking for loopholes.
The prospect of the future, accordingly, is on the whole pleasant and encouraging. It is only the backward glance, the gaze up the long vista of the past, that reveals anything alarming. Here the lines converge as they recede into the geological ages, and point to conclusions which, upon the theory, are inevitable, but by no means welcome. The very first step backwards makes the Negro and the Hottentot our blood-relations; — not that reason or Scripture objects to that, though pride may. The next suggests a closer association of our ancestors of the olden time with “our poor relations” of the quadrumanous family than we like to acknowledge. Fortunately, however,— even if we must account for him scientifically,-man with his two feet stands upon a foundation of his own. Intermediate links between the Bimana and the Quadrumana are lacking altogether; so that, put the genealogy of the brutes upon what footing you will, the four-handed races will not serve for our forerunners;— at least, not until some monkey, live or fossil, is producible with great-toes, instead of thumbs, upon his nether extremities; or until some lucky ‘geologist turns up the bones of his ancestor and prototype in France or England, who was so busy “napping the chuckie-stanes” and chipping out flint knives and arrow-beads in the time of the drift, very many ages ago,-before the British Channel existed, says Lyell,— and until these men of the olden time are shown to have worn their great-toes in a divergent and thumblike fashion. That would be evidence indeed: but until some testimony of the sort is produced, we must needs believe in the separate and special creation of man, however it may have been with the lower animals and with plants.
No doubt, the full development and symmetry of Darwin’s hypothesis strongly suggest the evolution of the human no less than the lower animal races out of some simple primordial animal,— that all are equally “lineal descendants of some few beings which lived long before the first bed of the Silurian system was deposited.”
Alas for Gray, his loopholes have been steadily closed.
I do like his conclusion, though — “uncanny” and “mischievous” are great virtues in a theory, I should think.
So the Darwinian theory, once getting a foothold, marches boldly on, follows the supposed near ancestors of our present species farther and yet farther back into the dim past, and ends with an analogical inference which “makes the whole world kin.” As we said at the beginning, this upshot discomposes us. Several features of the theory have an uncanny look. They may prove to be innocent: but their first aspect is suspicious, and high authorities pronounce the whole thing to be positively mischievous.
Now this is an interesting beast. It’s a 220 million year old fossil from China of an animal that is distinctly turtle-like. Here’s a look at its dorsal side:
Notice in the skull: it’s got teeth, not just a beak like modern turtles. The back is also odd, for a turtle. The ribs are flattened and broadened, but…no shell! It’s a turtle without a shell!
Got an hour? A good way to spend it would be to watch Neil Shubin lecture about digging in the arctic for fossil tetrapods.
I wonder if this is available in high-quality DVD format? I could see using this in the classroom.
Here’s another youtube bandwagon to jump on: I Am Darwin. Get in front of your webcam and talk about how Darwin has influenced you, concluding with “I am Darwin”, and send the youtube link to Tom Barbalet. How many Darwins are out there, anyway?
