development
pharyngula | September 27, 2006There are days when I simply cannot believe how dishonest the scoundrels at the Discovery Institute can be. This is one of them. I just read an essay by Jonathan Wells that is an appalling piece of anti-scientific propaganda, an extremely squirrely twisting of some science news. It's called "Why Darwinism is doomed", and trust me, if you read it, your opinion of Wells will drop another notch. And here you thought it was already in the gutter!
First, here's the science news that was published in Nature back in August, and which has set Wells off. The research is the result of the ability to…
pharyngula | September 26, 2006
It’s April (not anymore—it's September as I repost this), it’s Minnesota, and it’s snowing here (not yet, but soon enough). On days like this (who am I fooling? Every day!), my thoughts turn to spicy, garlicky delicacies and warm, sunny days on a lovely tropical reef—it’s a squiddy day, in other words, and I’ve got a double-dose of squidblogging on this Friday afternoon, with one article on the vampire squid, Vampyroteuthis infernalis, and this one, on squid evolution and cephalopod Hox genes.
Hox genes are members of a family of genes with a number of common attributes:
They all contain a…
purepedantry | September 26, 2006So I am sititng in a movie theater the other day, and some teenagers sitting behind me are talking. Of course, they are talking. They are ALWAYS talking behind me. And what particularly irks me is that it is a Tuesday night during the school year, and I only come to movies at 10 pm on Tuesday nights during the school year for the slim chance of avoiding talking teenagers.
Why, I ask you? Surely, there is some explanation for this behavior?
One theory is that teenagers are actually from a separate barbarian race. However, I suspect that there is also an underlying neurological reason…
pharyngula | September 25, 2006Awww. Take a look at the nice photography of adorable little frog embryos. The rest of the site also has some lovely photos of Australian fauna…I'd like to know what kind of camera/lens was used for those close-ups of frog embryos.
pharyngula | September 25, 2006
Hox genes are metazoan pattern forming genes—genes that are universally associated with defining the identities of regions of the body. There are multiple Hox genes present, and one of their unusual properties is that they are clustered and expressed colinearly. That is, they are found in ordered groups on the chromosome, and that the gene on one end is typically turned on first and expressed at the head end of the embryo, the next gene in order is turned on slightly later and expressed further back, and so on in sequence. That the tidy sequential order on the chromosome is associated with…
pharyngula | September 15, 2006
Via El PaleoFreak (in Spanish; here's a translation), I find this strange little cockatoo chick, and even better, take a look at these wonderful simulations of feather development.
pharyngula | September 14, 2006
We are all familiar with the idea that there are strikingly different kinds of eyes in animals: insects have compound eyes with multiple facets, while we vertebrates have simple lens eyes. It seems like a simple evolutionary distinction, with arthropods exhibiting one pattern and vertebrates another, but the story isn't as clean and simple as all that. Protostomes exhibit a variety of different kinds of eyes, leading to the suggestion that eyes have evolved independently many times; in addition, eyes differ in more than just their apparent organization, and there are some significant…
pharyngula | September 12, 2006This week, my students are thinking about SIDS,aging,Christiane Nusslein-Volhard,oncogenes,hunger,individuality,worm movies,obesity,sunscreen, and whether todivide or die. A fairly typical set of undergraduate concerns, right?
They've all also been reading chapters 3 and 4 of Carroll's Endless Forms Most Beautiful, and their summaries are here: α,β,γ,δ,ε, andζ.
If you missed it, here's Last week's digest and a brief explanation of what it's all about.
pharyngula | September 12, 2006I'm a little surprised at the convergence of interest in this news report of a conserved mechanism of organizing the nervous system—I've gotten a half-dozen requests to explain what it all means. Is there a rising consciousness about evo-devo issues? What's caused the sudden focus on this one paper?
It doesn't really matter, I suppose. It's an interesting observation about how both arthropods and vertebrates seem to partition regions along the dorso-ventral axis of the nervous system using exactly the same set of molecules, a remarkable degree of similarity that supports the idea of a common…
purepedantry | September 11, 2006Differing from the typical strategy of threatening potential suitors with castration, scientists speculate that phermones from fathers delay their daughters sexual development:
Chemical cues from fathers may be delaying the onset of sexual maturity in daughters, as part of an evolutionary strategy to prevent inbreeding, according to researchers at Penn State.
...
"Recently, experts elsewhere discovered a little-known pheromone receptor gene in the human olfactory system, linking the role of pheromones on menarche, or the first occurrence of menstruation," said Matchock, whose findings are…
pharyngula | September 10, 2006
I've been tinkering with a lovely software tool, the 3D Virtual Embryo, which you can down download from ANISEED (Ascidian Network of In Situ Expression and Embryological Data). Yes, you: it's free, it runs under Java, and you can get the source and versions compiled for Windows, Linux, and Mac OS X. It contains a set of data on ascidian development—cell shapes, gene expression, proteins, etc., all rendered in 3 dimensions and color, and with the user able to interact with the data, spinning it around and highlighting and annotating. It's beautiful!
Unfortunately, as I was experimenting with…
purepedantry | September 6, 2006Why we lay babies on their backs:
Research suggests that healthy newborn infants do not have what doctors call "nasoaxillary reflex" -- a protective reflex that helps keep their nasal passages open.
In adults lying on their side, the nasoaxillary reflex ensures that the uppermost nasal airway is open, Dr. Christopher O'Callaghan of the University of Leicester, UK, and colleagues explain in the journal Archives of Diseases of Childhood.
The researchers used acoustic rhinometry, a technique that measures nasal patency, to see whether the nasoaxillary reflex is present in 11 healthy term…
pharyngula | September 5, 2006I'm teaching a course in developmental biology this term, and as part of the coursework, I'm making students blog. The idea is to force them to ferret out instances of development in popular culture, in their personal experience, and/or in their reading—I'm not asking for treatises, but simply short articles that let me know their eyes are open. This year I'm also encouraging outsiders to take a look at and comment on what they're saying, so every week I'll be posting a round-up of links to the developmental biology blog…and here they are:
a human-specific gene
first neurons
Hox regulation…
pharyngula | August 30, 2006
We're only sorta bilaterally symmetric: superficially, our left and right halves are very similar, but dig down a little deeper, and all kinds of interesting differences appear. Our hearts are larger on the left than the right, our appendix is on the right side, even our brains have significant differences, with the speech centers typically on the left side. That there is asymmetry isn't entirely surprising—if you've got this long coil of guts with a little appendix near one end, it's got to flop to one side or the other—but what has puzzled scientists for a long time is how things so…
pharyngula | August 30, 2006
How do evolutionary novelties arise? The conventional explanation is that the first step is the chance formation of a genetic mutation, which results in a new phenotype, which, if it is favored by selection, may be fixed in a population. No one sensible can seriously argue with this idea—it happens. I'm not going to argue with it at all.
However, there are also additional mechanisms for generating novelties, mechanisms that extend the power of evolutionary biology without contradicting our conventional understanding of it. A paper by A. Richard Palmer in Science describes the evidence for an…
pharyngula | August 24, 2006
This article is part of a series of critiques of Jonathan Wells' The Politically Incorrect Guide to Darwinism and Intelligent Design that will be appearing at the Panda's Thumb over the course of the next week or so. Previously, I'd dissected the summary of chapter 3. This is a longer criticism of the whole of the chapter, which is purportedly a critique of evo-devo.
Jonathan Wells is a titular developmental biologist, so you'd expect he'd at least get something right in his chapter on development and evolution in The Politically Incorrect Guide to Darwinism and Intelligent Design, but no:…
pharyngula | August 20, 2006You can get a jump on the class—I've posted a list of the textbooks you'll need on the class website.
pharyngula | August 14, 2006Tanystylum bealensis male, ventral view, showing eggs and instar 1 (protonymphon) on
ovigerous legs. in. 1, instar 1 (protonymphon); pa, palp; pr, proboscis; 1, first walking leg; 2, second
walking leg; 3, third walking leg; 4, fourth walking leg.
Surely, you haven't had enough information about pycnogonids yet, have you? Here's another species, Tanystylum bealensis, collected off the British Columbian coast. That's a ventral view of the male, and those bunches of grapes everywhere are eggs and babies—males do the childcare in this group. These animals also live in relatively shallow water,…
pharyngula | August 8, 2006
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…
pharyngula | August 3, 2006Often, as I've looked at my embryonic zebrafish, I've noticed their prominent median fins. You can see them in this image, although it really doesn't do them justice—they're thin, membranous folds that make the tail paddle-shaped.
These midline fins are everywhere in fish—lampreys have them, sharks have them, teleosts have them, and we've got traces of them in the fossil record. Midline fins are more common and more primitive, yet usually its the paired fins, the pelvic and pectoral fins, that get all the attention, because they are cousins to our paired limbs…and of course, we completely…