development
pharyngula | July 30, 2007
People are always arguing about whether primitive apes could have evolved into men, but that one seems obvious to me: of course they did! The resemblances are simply too close, so that questioning it always seems silly. One interesting and more difficult question is how oysters could be related to squid; one's a flat, sessile blob with a hard shell, and the other is a jet-propelled active predator with eyes and tentacles. Any family resemblance is almost completely lost in their long and divergent evolutionary history (although I do notice some unity of flavor among the various molluscs,…
pharyngula | July 18, 2007Of course Denyse O'Leary defends Pivar — any crackpot in denial about evolution is a friend of the IDists. They do point out a bizarre flaw in Wikipedia, though, and a common mangling of a concept.
There is an idea that's been around for almost a century, the morphogenetic field. This is a concept in developmental biology that refers to a local domain of interactions that work independently of more global factors to assemble an organ. For instance, we can talk about a limb field or an eye field, and it identifies a patch of tissue that is dedicated to a particular developmental task, and that…
pharyngula | June 24, 2007Jason Rosenhouse has dug into the details of the evo-devo chapter of Behe's The Edge of Evolution and found some clear examples of dishonest quote-mining (so what else is new, you may be thinking—it's what creationists do). I've warned you all before that when you see an ellipsis in a creationist quote, you ought to just assume that there's been something cut out that completely contradicts the point the creationist is making; Rosenhouse finds that Behe gets around that little red-flag problem by simply leaving out the ellipses.
I just want to expand a little bit on one point Behe mangles and…
pharyngula | June 23, 2007
The general pattern of developing positional information in Drosophila starts out relatively simply and gets increasingly complicated as time goes by. Initially, there is a very broad distribution of a gradient of a maternal morphogen. That morphogen then triggers the expression of narrower (but still fairly broad) bands of aperiodic gap genes. The next step in this process is to turn on sets of genes in narrow, periodic bands that correspond to body segments. This next set of genes are called the pair-rule genes, because they do something surprising and rather neat: they are turned on in…
purepedantry | June 5, 2007A great article in the NYTimes about the debate over a sensory integration disorder:
The problem, these therapists say, is in the brain, which is not properly integrating the onslaught of information coming through the senses, often causing anxiety, tantrums and problems in the classroom. Such difficulties, while common in children with developmental disorders like autism, also occur on their own in many otherwise healthy youngsters, they say.
No one has a standard diagnostic test for these sensory integration problems, nor any idea of what might be happening in the brain. Indeed, a diagnosis…
pharyngula | June 3, 2007One of the common principles used to characterize the rules of growth in developing systems is the idea of allometry. Here, I'll briefly summarize the concept with a few clear illustrations and a tiny amount of simple math.
"Allometry" means "different growth or measurement", and it refers to the fact that different body parts grow at different rates during development—we aren't simply linearly scaled up versions of our younger selves, but instead we have different proportions. One vivid and familiar example is the growth of our heads. Look at a baby, and their heads and eyes seem huge…
pharyngula | June 2, 2007In chapter 14 of the Origin of Species, Darwin wondered about the whole process of metamorphosis. Some species undergo radical transformations from embryo to adult, passing through larval stages that are very different from the adult, while others proceed directly to the adult form. This process of metamorphosis is of great interest to both developmental and evolutionary biologists, because what we see are major transitions in form not over long periods of time, but within a single generation.
We are so much accustomed to see a difference in structure between
the embryo and the adult, that we…
pharyngula | June 1, 2007The Discovery Institute is so relieved — they finally found a textbook that includes a reworked version of Haeckel's figure. Casey Luskin is very excited. I'm a little disappointed, though: apparently, nobody at the Discovery Institute reads Pharyngula. I posted a quick summary in September of 2003 that went through several textbooks, and showed a couple of examples where redrawn versions of Haeckel's diagram were used. More recently, I posted a fairly exhaustive survey by Patrick Frank of the use of that diagram since 1923, which showed that it was rare, and that the concept of…
pharyngula | May 25, 2007We've often heard this claim from creationists: "there is no way for genetics to cause an increase in complexity without a designer!". A recent example has been Michael Egnor's obtuse caterwauling about it. We, including myself, usually respond in the same way: of course it can. And then we list examples of observations that support the obviously true conclusion that you can get increases in genetic information over time: we talk about gene duplication, gene families, pseudogenes, etc., all well-documented manifestations of natural processes that increase the genetic content of the organism.…
pharyngula | May 22, 2007Here are three animals. If you had to classify them on the basis of this superficial glimpse, which two would you guess were most closely related to each other, and which one would be most distant from the others?
On the left is a urochordate, an ascidian, a sessile, filter-feeding blob that is anchored to rocks or pilings and sucks in sea water to extract microorganismal meals. In the middle is a cephalochordate, Amphioxus, also a filter feeder, but capable of free swimming. On the right are some fish larvae. All are members of the chordata, the deuterostomes with notochords. If you'd…
pharyngula | May 16, 2007Hey, you want some science? My latest Seed column on battling beetle balls is online.
(And I've just arrived in Ann Arbor after a long travel day!)
purepedantry | May 16, 2007No, this is not like voodoo prediction where they will know what will happen 12 years hence.
All of us, however, are capable in degrees of predicting what is going to happen over short time scales. This predicition falls into two general categories. First, we can predict the behavior of inaminate objects such as knowing how a ball will flight when we hit it just-so with a bat. That implies that we understand how physics work on some inituitive level.
Second, we can understand how animate objects such as people behave. For example, if I see someone removing objects from a container…
worldsfair | May 15, 2007"In the simplest terms, gastrulation is a stage in early development; in human beings it occurs between two and three weeks after fertilization. It is that stage when a two-layered cell mass undergoes a set of specific movements and interactions that establish the three germ layers of the embryo (endoderm, mesoderm, and ectoderm) and the beginnings of a three-dimensional structure. The end result doesn't look like much of an animal, but it has set up pools of cells that will contribute to specific future cell types, and has laid down the rough outline of tissues along the body axis."
(Click…
worldsfair | May 15, 2007"The pharyngula stage: the pharyngula is a vertebrate embryo that has assembled the outlines of the body plan. It has the key features of vertebrate morphology -- a post-anal tail, a notochord, a dorsal neural tube, a segmented musculature, and an array of branchial arches ("gill" arches). The major organs have begun to form."
(Click here to go to post)
pharyngula | May 15, 2007Didn't I just say "Woo hoo" yesterday? False alarm. Scarcely do I clear one set of major tasks away than another set rise up. I already mentioned that I was going to be the speaker at the Humanists of Minnesota banquet on Saturday evening. I neglected to tell you all that I'm leaving for the University of Michigan tomorrow to give the keynote at the Genetic Programming Theory and Practice Workshop.
I know virtually nothing about genetic programming, so this is a wonderful opportunity to learn something about it.
Since I'm certainly not going to be able to tell them a thing about genetic…
pharyngula | May 12, 2007This is a beautifully done movie, although it does get a bit silly in the end.
One point this brought to mind: have you ever looked at sperm? They're amazing. We humans do go through a single-celled haploid stage which is the focus of some very intense selection pressure, and humans in their haploid phase possess some impressive abilities. No brains, but the sperm are motile and exhibit seeking behavior. Eggs are also wonderful — they are precisely balanced on the edge of criticality, ready to erupt into a cascade of changes with a single stimulus. It's easy to dismiss gametes as blobs and…
pharyngula | May 8, 2007My previous contributions to the basic concepts in science collection were on gastrulation and neurulation, so let's add the next stage, and the one I named the blog after: the pharyngula.
First, though, a few general remarks on developmental stages. In some ways, these are somewhat arbitrary: development is an ongoing process, a real continuum, and what we're doing is picking recognizable moments where we think we see real transitions and highlighting those as significant markers. They can be somewhat fuzzy, although in early development in particular, when the organism is simple, we can…
pharyngula | May 4, 2007Way back in the early 19th century, Geoffroy St. Hilaire argued for a radical idea, that vertebrates and most invertebrates were inverted copies of each other. Vertebrates have a dorsal nerve cord and ventral heart, while an insect has a ventral nerve cord and dorsal heart. Could it be that there was a common plan, and that one difference is simply that one is upside down relative to the other? It was an interesting idea, but it didn't hold up at the time; critics could just enumerate the multitude of differences observable between arthropods and vertebrates and drown out an apparent…
pharyngula | April 5, 2007A hagfish egg with a 14.3-mm pharyngula-stage embryo inside (arrows). Scale bar, 5 mm.
I've been looking forward to seeing these little jewels in print since I saw Kuratani talk about them at the SICB meetings in January. Hagfish are wonderfully slimy jawless chordates that have been difficult to raise in the lab—although if you poke a whale corpse rotting in the cold deeps you'll find them swarming everywhere. The Kuratani lab has managed to keep animals of the species Eptatretus burgeri alive and healthy in a lab aquarium maintained at cold temperatures (16°C), and has even had success in…
pharyngula | April 3, 2007This evening, I am watching an episode of that marvelous and profane Western, Deadwood, as I type this; it is a most excellently compensatory distraction, allowing me to sublimate my urge to express myself in uncompromisingly vulgar terms on Pharyngula. This is an essential coping mechanism.
I have been reading Jonathan Wells again.
If you're familiar with Wells and with Deadwood, you know what I mean. You'll just have to imagine that I am Al Swearingen, the brutal bar-owner who uses obscenities as if they were lyric poetry, while Wells is E.B. Farnum, the unctuous rodent who earns the…