development
pharyngula | April 18, 2006
It always gives a fellow a warm feeling to see an old comrade-in-arms publish a good paper. Chris Cretekos was a graduate student working on the molecular genetics of zebrafish at the University of Utah when I was a post-doc there, and he's a good guy I remember well…so I was glad to see his paper in Developmental Dynamics. But then I notice it wasn't on zebrafish—Apostate! Heretic!
Except…it's on bats. How cool is that? And it's on the embryonic development of bats. Even cooler! I must graciously forgive his defection from the zebrafish universe since he is working on an organism that is…
pharyngula | April 14, 2006Science asks awkward questions, doesn't it? I got a link to a recent paper in the BMJ (thanks, SEF!) that asks one of those questions—can fetuses feel pain?—and then takes it apart clinically, coming up with an answer that will make some adults feel pain: that answer is no.
The first step is to work out when the machinery of the nervous system is first present, and when it is simply possible for the fetus to detect unpleasant stimuli. The nervous system has its beginnings early in development, with neurulation at around 3 weeks after fertilization, but it is initially little more than a…
pharyngula | April 5, 2006My wife thought this story about left-handed snails having a competitive advantage, in that they seem to be better able to escape predation by right-handed crabs, was pretty cool. She also recalled that I'd scribbled up something about snail handedness before, so to jump on the bandwagon, I've brought those stories over from the old site.
The handedness of snail shells is a consequence of early spiral cleavages in the blastula. It's a classic old story in developmental biology—everyone ought to know it!
There was also a story last year about shell chirality in Euhadra. There, it wasn't a…
pharyngula | April 5, 2006
Developmental biologists are acutely interested in asymmetries in development: they are visible cues to some underlying regional differences. For instance, we'd like to know the molecules and interactions involved in taking a seemingly featureless sphere, the egg, and specifying one side to go on to form a head, and the the opposite side to form a tail. We'd like to understand why our back (or dorsal) side looks different from our belly (or ventral) side. One particularly intriguing distinction, though, is the left-right axis. For the most part, left and right are nearly identical, mirror-…
pharyngula | April 3, 2006There are these fossilized embryos from the Ediacaran, approximately 570 million years ago, that have been uncovered in the Doushantuo formation in China. I've mentioned them before, and as you can see below, they are genuinely spectacular.
Parapandorina raphospissa
But, you know, I work with comparable fresh embryos all the time, and I can tell you that they are incredibly fragile—it's easy to damage them and watch them pop (that's a 2.3MB Quicktime movie), and dead embryos die and decay with amazing speed, minutes to hours. Dead cells release enzymes that trigger a process called autolysis…
pharyngula | March 28, 2006
A while back, I criticized this poorly implemented idea from Paul Nelson of the Discovery Institute, a thing that he claimed was a measure of organismal complexity called Ontogenetic Depth. I was not impressed. The short summary of my complaints:
Unworkable idea: There was no explanation about how we could implement and test the idea, and despite promises at the time, Nelson still hasn't produced his methods.
False assertions and confusing examples: He claims that all changes in early lineages are destructive, for instance, which is false.
Bad metaphors: He uses a terribly flawed metaphor…
pharyngula | March 20, 2006
What has always attracted me to developmental biology is the ability to see the unfolding of pattern—simplicity becomes complexity in a process made up of small steps, comprehensible physical and chemical interactions that build a series of states leading to a mostly robust conclusion. It's a bit like Conway's Game of Life in reverse, where we see the patterns and can manipulate them to some degree, but we don't know the underlying rules, and that's our job—to puzzle out how it all works.
Another fascinating aspect of development is that all the intricate, precise steps are carried out…
pharyngula | March 7, 2006
I'm teaching my developmental biology course this afternoon, and I have a slightly peculiar approach to the teaching the subject. One of the difficulties with introducing undergraduates to an immense and complicated topic like development is that there is a continual war between making sure they're introduced to the all-important details, and stepping back and giving them the big picture of the process. I do this explicitly by dividing my week; Mondays are lecture days where I stand up and talk about Molecule X interacting with Molecule Y in Tissue Z, and we go over textbook stuff. I'm…
pharyngula | February 27, 2006Bone is a sophisticated substance, much more than just a rock-like mineral in an interesting shape. It's a living tissue, invested with cells dedicated to continually remodeling the mineral matrix. That matrix is also an intricate material, threaded with fibers of a protein, type II collagen, that give it a much greater toughness—it's like fiberglass, a relatively brittle substance given resilience and strength with tough threads woven within it. Bone is also significantly linked to cartilage, both in development and evolution, with earlier forms having a cartilaginous skeleton that is…
pharyngula | February 22, 2006
My daughter is learning about evolution in high school right now, and the problem isn't with the instructor, who is fine, but her peers, who complain that they don't see the connections. She mentioned specifically yesterday that the teacher had shown a cladogram of the relationships between crocodilians, birds, and mammals, and that a number of students insisted that there was no similarity between a bird and an alligator.
I may have to send this news article to school with her: investigators have found that a mutation in chickens causes them to develop teeth—and the teeth resemble those of…
pharyngula | February 20, 2006
When male squid get together with their female friends, they have a couple of nuptial options: they can go ahead and use their charm to court the female, or they can just start poking her with tentacles full of sperm in mating frenzy. Now some of you guys might be thinking the latter option sounds good (what's the point of living the life of a squid if you can't be selfish and uninhibited, right?), while the ladies and gentlemen here might think the former is better. A study of the mating behavior of squid close-up and in the lab suggests that it's true: taking one's time and mating…
pharyngula | February 20, 2006
Doesn't everyone just love cephalopods? I find them to be a fascinating example of a body plan radically different from our own, the closest thing to a truly alien large metazoan on our planet. I try to keep my eyes open for new papers on cephalopod development, but unfortunately, they are rather difficult to study and data is sadly thin and tantalizing.
I just ran across a pair of papers by Jantzen and Havenhand (2003a, b) on squid mating. That's close enough to development for me!
First, let me explain a few general features of squid sex. Males produce elaborate spermatophores,…
pharyngula | February 18, 2006
Once upon a time, I was one of those nerds who hung around Radio Shack and played about with LEDs and resistors and capacitors; I know how to solder and I took my first old 8-bit computer apart and put it back together again with "improvements." In grad school I was in a neuroscience department, so I know about electrodes and ground wires and FETs and amplifiers and stimulators. Here's something else I know: those generic components in this picture don't do much on their own. You can work out the electrical properties of each piece, but a radio or computer or stereo is much, much more than a…
pharyngula | February 8, 2006Here's some very cool news: scientists have directly observed the evolution of a complex, polygenic, polyphenic trait by genetic assimilation and accommodation in the laboratory. This is important, because it is simultaneously yet another demonstration of the fact of evolution, and an exploration of mechanisms of evolution—showing that evolution is more sophisticated than changes in the coding sequences of individual genes spreading through a population, but is also a consequence of the accumulation of masked variation, synergistic interactions between different alleles and the environment,…
razib | January 26, 2006Over the past 5 years Matthew Harris has been doing some interesting research into feather morphogenesis, and he has produced some must watch videos. His work on quantitative modeling of development via the activator-inhibitor system is, I believe, a necessary precursor in fruitfully talking about the evolutionary context of feathers. To my mind the videos are essential for anyone who isn't fluent in molecular developmental biology (like me), so we can have the big picture in mind when digging through the essential details.
pharyngula | January 24, 2006
First, a tiny bit of quantitative morphological data you can find in just about any comparative anatomy text:
mammal
number of vertebrae
cervical
thoracic
lumbar
sacral
caudal
horse
7
18
6
5
15-21
cow
7
13
6
5
18-20
sheep
7
13
6-7
4
16-18
pig
7
14-15
6-7
4
20-23
dog
7
13
7
3
20-23
human
7
12
5
5
3-4
The number of thoracic vertebrae varies quite a bit, from 9 in a species
of whale to 25 in sloths. The numbers of lumbar, sacral, and more caudal vertebrae also show considerable variation. At the same time, there is a surprising amount of invariance in the number of cervical…
pharyngula | January 19, 2006
Nematostella, the starlet anemone, is a nifty new model system for evo-devo work that I've mentioned a few times before—in articles on "Bilateral symmetry in a sea anemone" and "A complex regulatory network in a diploblast"—and now I see that there is a website dedicated to the starlet anemone and a genomics database, StellaBase. It's taking off!
pharyngula | January 19, 2006
Variation is common, and often lingers in places where it is unexpected. The drawing to the left is from West-Eberhard's Developmental Plasticity and Evolution(amzn/b&n/abe/pwll), and illustrates six common variations in the branching pattern of the aortic arch in humans. These are differences that have no known significance to our lives, and aren't even visible except in the hopefully rare situations in which a surgeon opens our chests.
This is the kind of phenomenon in which I've become increasingly interested. I work with a model system, the zebrafish, and supposedly one of the…
pharyngula | January 16, 2006This is a post originally made on the old Pharyngula website; I'll be reposting some of these now and then to bring them aboard the new site.
There are a number of reasons why the current theory of evolution should be regarded as incomplete. The central one is that while "nothing in biology makes sense except in the light of evolution", some important disciplines within biology, development and physiology, have only been weakly integrated into the theory.
Raff (1996) in his book The Shape of Life(amzn/b&n/abe/pwll) gives some of the historical reasons for the divorce of evolution and…
pharyngula | January 16, 2006The Hwang Woo Suk stem cell research scandal has triggered quite a bit of concerned introspection in the scientific community. Orac has some useful comments on a good article in the NY Times that makes the distinction between "frontier science" and "textbook science", where much of the current stem cell research is clearly on the frontier.
Much of science at the very frontiers turns out not to be correct. However, the way it is all too often reported in the press is that it is correct. We in science understand the difference between textbook science and the sort of frontier science that makes…