Here’s a website of mutating pictures, a collection of images made with a splatter of scattered triangles. Your job is to browse through them and score them for how much they resemble a face — which isn’t easy. If I stare at any random pile of symmetrical shadings, they all start to look like faces to me.
Anyway, pictures that get higher scores produce more progeny, with slight mutations, in the next round of picture generation. You can see where this is going…
One concept that is sometimes used in developmental biology is the idea of the “master control gene” or “master switch” — a single gene whose expression is both necessary and sufficient to trigger activation of many other genes in a coordinated fashion, leading to the development of a specific tissue or organ. It’s a handy concept on which to hang a discussion of transcription factors, but it may actually be of rather limited utility in the real world of molecular genetics: there don’t seem to be a lot of examples of master control genes out there! Pax-6 is the obvious one, a gene that initiates development of the eye, and other genes may be mentioned in certain stem cell pathways, but even in the eyes of vertebrates, for example, eye development is more complicated than a single switch, and similarly, many other developmental processes seem to use multiple or redundant regulatory controls — the cases where we have a single gene bottleneck are either rare or poorly represented in the literature.
They’re still at least pedagogically useful, though — it’s a simple case of imposition of a specific developmental pathway on a patch of tissue.
T. Ryan Gregory is turning into quite the coiner of useful terms. The latest: Dog’s Ass Plots. It refers specifically to charts that try to make a case for the evolution of complexity by selectively encoding their creator’s assumptions about the topic, and especially by oversimplifying the data in a way that skews their interpretation.
I suspect DAPs are a problem in other fields as well, though.
I’ve just come back from my introductory biology classroom in which I’ve been trying hard to convince students of an important historical fact: the scientists, especially the geologists, who came up with the idea that the earth was old were working in a Christian tradition, and they came up with their ideas because they needed to explain the evidence, not because they were driven by theological considerations or because they had been bribed by the Evil Atheist Conspiracy. Sometimes you just have to put them in the shoes of a geologist in 1850 to get them to see the true motives. Then I discover that ChrisR is also trying to make the point, that it’s the evidence not ideology that informs our conclusions.
It’s our studies of the rock record that have led geologists to propose that the Earth is so unimaginably old, not the edicts of the Evil Secular Conspiracy. When we observe huge angular unconformities, where rocks have been tilted almost vertically, eroded and then covered with flat-lying rocks, we see that they require a large period of time to have formed. When thermodynamics tells us that it would take tens of thousands of years for an ingneous intrusion hundreds of metres across to solidify from lava, we assume that that means it tooks tens of thousands of years to form. When present day estimates of sea floor spreading – measured in mm per year – match those estimated from the increased radiometric ages of the ocean floor away from the Mid-Atlantic Ridge, we conclude the Atlantic Ocean has been formed after tens of millions of years of slow continental drift. The list goes on and on; and useful as the fossil record is, I could continue for quite a while without having to mention the E-word.
I was also trying to get across another piece of evidence that the biologists were trying (and before Darwin, failing) to interpret, one that is quite ironic now. One of the big questions before natural historians was to explain all the gradations of form in the natural world — why are there so many species of mouse, for instance, that vary in little ways, and why are there ‘mouse-like’ forms that are larger, like rats? Why is the world swimming in transitional forms, and why aren’t animals more distinct from one another, in other words?
It’s a sign of the degeneracy of the modern creationist that instead of grappling with these questions honestly, as the 19th century creationists/natural historians did, they instead simply deny the existence of the evidence. Like Chris says, rocks aren’t coy about their age, and I’d add that organisms aren’t hiding their relationships.
Laelaps explains the basic concepts of horse evolution. Now if only we could get the creationists to actually read that summary — they keep saying that the evolution of the horse has been disproven by the fossil record.
There is a painful assumption of progress in many interpretations of evolution — and sometimes it’s by people who ought to know better. T. Ryan Gregory finds a ghastly example of a figure that, by cherry-picking the data and doing a little suggestive ordering of the presentation, makes it look like there’s a correlation between the amount of non-coding DNA and organismal complexity. Fortunately, he counters it with a much more useful chart (that I’m definitely stealing for the next time I teach genetics) with no such bias.
And then Larry Moran tops Gregory with an even worse figure. I don’t quite understand it; maybe this distortion of the evidence to support progress, increasing molecular complexity, and the superiority of humans has roots in misunderstandings before my time, because my genetics and cell biology instructors in the 1970s sure didn’t promote this nonsense then. We were told even in those ancient days that the C-value paradox wasn’t a problem if you didn’t try to shoehorn mammals into a position at the pinnacle of evolution.
Maybe I just had really good professors. Thanks, Arthur Whiteley and Larry Sandler!
Whenever I spot some old thread suddenly getting a surge of new comments, I can guess what has happened: a creationist or two has come to visit. That’s happening right now on this very short article that mentions the peppered moths; we’re up above 200 comments now, and it seems to have very little to do with moths anymore. Instead, we’ve got a creationist complaining about the absence of transitional species and the Cambrian ‘explosion’, with a little quote-mining of Richard Dawkins. You commenters are taking care of him ably, but there are just a few things I want to mention, and a few questions I want to ask of the creationists.
I got some email today with lots of constructive suggestions (See? Not all my email is evil!) for how we ought to change the education of biology students — such as by giving them a foundation in the history and philosophy of our science, using creationist arguments as bad examples so the students can see the errors for themselves, etc. — and it was absolutely brilliant, even the parts where he disagreed with some things I’d written before. Best email ever!
Of course, what helped is that I spent my summer “vacation” putting together a new freshman first semester course for biology majors that I’m teaching for the first time right now, and it’s exactly the course he described. It was eerie, like one of my future students had invented a time machine and come back into the past to tell me what to do. A lot of the course content is locked up behind a password-protected firewall, I’m afraid, but just to show you what I’m talking about, I’ll put the course schedule below the fold.
When we look at the face of another person, we can recognize specific features that have familial resemblances. In my family, for instance, I can recognize a “Myers nose” that my grandmother and my father and some of my siblings and kids have, and it’s different than my wife’s or my mother’s nose. These are subtle differences in shape—a bit of a curve, a knob, a seam—and their inheritance suggests that these differences are specified somehow in the DNA. If you think about it, though…how can whether the profile of a nose is straight or curved be encoded in a linear stretch of nucleotides? The complicated answer is that it isn’t—morphology is a consequence of epigenetic interactions during development—but we know that the alleles present in the genome do contribute in some significant way to three-dimensional form. How?
We don’t know all the details. This is one of those huge research problems that has gaping holes, full of promise and interest, where we don’t understand exactly how all the pieces fit together. However, here’s an important point that is relevant to other, larger issues in evolution: even where we lack full information about mechanisms, we can roughly perceive the shape of the answer, and that helps us rule out many alternative explanations and guides us in the general direction of a more complete understanding.
People’s noses are a difficult subject for research; we don’t get to define human crosses, people tend to be a little snippy about telling them who to breed with and taking their genes apart, and humans are awfully slow to breed. Fish are better experimental animals, much more pliable and faster and more prolific in their breeding. Some fish, such as the African cichlids, also have highly diverse populations and species with easily recognized and often quite dramatic morphological differences—and we can explore how those differences are generated by genetic and molecular differences in development. In particular, we can start to figure out how fish jaws are shaped by developmental processes.
Scott Lanyon, director of the Bell Museum, has an article on two disease we should worry about, VHSv and EAS.
Personally, I think VHSv is the worst. It’s a virus that causes hemorrhagic septicemia in fish; just from the name you know it’s bad, involving blood and sepsis. My most horrible experience raising zebrafish was the time hemorrhagic septicemia swept through my colony and I had to euthanize every animal and bleach every last bit of plumbing to eradicate it. This disease has been detected in waters of Wisconsin, and it’s definitely not good.
EAS may not be as dramatically gory and lethal in its effects, but it strikes humans directly. It’s Evolution Avoidance Syndrome, and it causes the brains of scientists and journalists to seize up when circumstances are appropriate to discuss evolution in public. Apparently, we want local fish populations to develop, acquire, improve or have arise resistance to the hemorrhagic septicemia virus; we can’t possibly suggest that evolution might be at work.
