Here’s an interesting thought and modeling experiment: how to evolve a watch, literally.
As an example, it’s nice, but there are also real biological examples of organisms evolving clocks — evolution of the period gene, for instance, which also shows evidence of being calibrated to day lengths by natural processes, or the somitic clock. Most organisms on the planet seem to have multiple clocks built right into them, and they’ve all evolved.
(via No More Mr. Nice Guy!)
You want a useful, practical, obvious example of evolution in action? Try this summary of corn evolution.
(via ERV)
I was just turned on to this recent issue of the McGill Journal of Education which has the theme of teaching evolution. It’s a must-read for science educators, with articles by UM’s own Randy Moore, Robert Pennock, Branch of the NCSE, and Eugenie Scott, and it’s all good. I have to call particular attention the article by Massimo Pigliucci, “The evolution-creation wars: why teaching more science just is not enough”, mainly because, as I was reading it, I was finding it a little freaky, like he’s been reading my mind, or maybe I’ve been subconsciously catching Pigliucci’s psychic emanations. I think I just need to tell everyone to do exactly what this guy says.
So that’s what Carl Buell has been up to…Donald Prothero and Carl have been working on a new book, Evolution: What the Fossils Say and Why It Matters(amzn/b&n/abe/pwll), containing descriptions of important transitional fossils, and as you can tell from the title, directly countering some of the silly claims of the creationists. This is going to be one of those books everyone must have.
To whet your appetite, Carl sent along one of the many color plates that will be in the book—this is Sinodelphys, a 125 million year old marsupial.
You’re already drooling, aren’t you? You want this book. You must have this book. It’s less than $30 at Amazon; it’s not available just yet, but any moment now…so pre-order it already!
My latest column for Seed is now available online. It’s an abbreviated summary of how vertebrates make segments (so it’s illustrated with a fly…), with special emphasis on the global and clocklike mechanism we use.
I was sitting down this evening to write up this nifty new paper from the Carroll lab, when I noticed that Carl Zimmer beat me to it. Dang. There are all these other bloggers around here, and it’s hard to keep on top of all of them, all at once.
Go read it anyway. It’s good stuff, all about the importance of regulatory changes in evolution.
Early Cambrian shrimp! I just had to share this pretty little fellow, a newly described eucrustacean from the lower Cambrian, about 525 million years ago. It’s small — the larva here is about 1.8mm long, and the adults are thought to have been 3mm long — but it was probably numerous, and I like to imagine clouds of these small arthropods swarming in ancient seas.
I’ve written a long introduction to the work I’m about to describe, but here’s the short summary: the parts of organisms are interlinked by what has historically been called laws of correlation, which are basically sets of rules that define the relationship between different characters. An individual attribute is not independent of all others: vary one feature, and as Darwin said, “other modifications, often of the most unexpected nature, will ensue”.
Now here’s a beautiful example: the regulation of the growth of mammalian molars. Teeth have long been a useful tool in systematics—especially in mammals, they are diverse, they have important functional roles, and they preserve well. They also show distinct morphological patterns, with incisors, canines, premolars, and molars arranged along the jaw, and species-specific variations within each of those tooth types. Here, for example, is the lower jaw of a fox. Look at the different kinds of teeth, and in particular, look at the differences within just the molars.
Note that in this animal, there are three molars (the usual number for most mammals, although there are exceptions), and that the frontmost molar, M1, is the largest, M2 is the second largest, and M3, the backmost molar, is the smallest. This won’t always be the case! Some mammals have a larger M3, and others may have three molars of roughly equal size. What rules regulate the relative size of the various molars, and are there any consistent rules that operate across different species?
To answer those questions, we need to look at how the molars develop, which is exactly what Kavanagh et al. have done.
John Dennehy’s citation classic this week is The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme, by Gould and Lewontin. It’s one of my favorite papers of all time — if you haven’t read it, you should do so now. It contains a set of ideas that are essential to understanding evo-devo.
Gould always struck me as a closet developmental biologist — he should have studied it more!
Cuvier, and his British counterpart, Richard Owen, had an argument against evolution that you don’t hear very often anymore. Cuvier called it the laws of correlation, and it was the idea that organisms were fixed and integrated wholes in which every character had a predetermined value set by all the other characters present.
In a word, the form of the tooth involves that of the condyle; that of the shoulder-blade; that of the claws: just as the equation of a curve involves all its properties. And just as by taking each property separately, and making it the base of a separate equation, we should obtain both the ordinary equation and all other properties whatsoever which it possesses; so, in the same way, the claw, the scapula, the condyle, the femur, and all the other bones taken separately, will give the tooth, or one another; and by commencing with any one, he who had a rational conception of the laws of the organic economy, could reconstruct the whole animal.
Cuvier famously (and incorrectly) argued that he could derive the whole of the form of an animal from a single part, and that this unity of form meant that species were necessarily fixed. An organism was like a complex, multi-part equation that used only a single variable: you plugged a parameter like ‘ocelot’ into the Great Formula, and all the parts and pieces emerged without fail; plug in a different parameter, say ‘elephant’, and all the attributes of an elephant would be expressed. By looking at one element, such as the foot, you could determine whether you were looking at an elephant or an ocelot, and thereby derive the rest of the animal.
