Since I was asked what a cnidarian “head” is in reference to this work on multi-headed cnidarians, I’ll answer. In short, they don’t have one.
Pharyngula
Evolution, development, and random biological ejaculations from a godless liberal
Since I was asked what a cnidarian “head” is in reference to this work on multi-headed cnidarians, I’ll answer. In short, they don’t have one.
One of the traditional ways to explain a scientific subject is the historical approach: start at the beginning of the endeavor and explain why people asked the questions they did, how they answered them, and how each answer blossomed into new potential. It’s a popular way of teaching science, too, because it emphasizes the process that leads to new discovery. Middle World: The Restless Heart of Matter and Life(amzn/b&n/abe/pwll), by Mark Haw, exemplifies the technique. Not only is it effective, but this one slim book manages to begin with a simple, curious observation in 1827 and ends up synthesizing many of the major ideas of modern physics, chemistry, and biology!
We now have a draft of the sea anemone genome, and it is revealing tantalizing details of metazoan evolution. The subject is the starlet anemone, Nematostella vectensis, a beautiful little animal that is also an up-and-coming star of developmental biology research.
A most important reason for this work is that the anemone Nematostella is a distant relative of many of the animals that have already been sequenced, and so provides an essential perspective on the evolutionary changes that we observe in those other organisms. Comparison of its genome with that of other metazoans is helping us decipher the likely genetic organization of the last common ancestor of all animals.
Albert Mohler might be freaking out at some of the new biotechnologies, but he missed a big one, one that might give him nightmares: synthetic biology. This week’s Nature has a very fine editorial on a subject that’s probably going to be more troubling to the religious than evolution, in a few years. We’re on the verge of being able to create life in the laboratory.*
Synthetic biology provides a welcome antidote to chronic vitalism.
Many a technology has at some time or another been deemed an affront to God, but perhaps none invites the accusation as directly as synthetic biology. Only a deity predisposed to cut-and-paste would suffer any serious challenge from genetic engineering as it has been practised in the past. But the efforts to design living organisms from scratch —; either with a wholly artificial genome made by DNA synthesis technology or, more ambitiously, by using non-natural, bespoke molecular machinery —; really might seem to justify the suggestion, made recently by the ETC Group, an environmental pressure group based in Ottawa, Canada, that “for the first time, God has competition”.That accusation was levelled at scientists from the J. Craig Venter Institute in Rockville, Maryland, based on the suspicion that they had synthesized an organism with an artificial genome in the laboratory. The suspicion was unfounded, but this feat will surely be achieved in the next few years, judging from the advances reported earlier this month at the Kavli Futures Symposium in Ilulissat, Greenland, on the convergence of synthetic biology and nanotechnology, and the progress towards artificial cells.
What’s particularly refreshing about the article is that it downplays the creation of life in the lab—it’s going to be an impressive technical achievement, but it will not be a “momentous step.” There is no wide chasm between chemistry and life, and crossing that threshold shouldn’t (and won’t, I expect, unless the politicking is particularly effective) be a Nobel-winning accomplishment, nor is it going to surprise anyone. In the next generation, it’s going to be taken for granted as just part of biochemistry, just like no organic chemists are shaken up by the routine synthesis of urea anymore.
It ought to shake up the social consciousness, though: another bastion of vitalism will have fallen. It ought to shift a few attitudes about some common issues, too.
Synthetic biology’s view of life as a molecular process lacking moral thresholds at the level of the cell is a powerful one. And it can and perhaps should be invoked to challenge characterizations of life that are sometimes used to defend religious dogma about the embryo. If this view undermines the notion that a ‘divine spark’ abruptly gives value to a fertilized egg —; recognizing as it does that the formation of a new being is gradual, contingent and precarious —; then the role of the term ‘life’ in that debate might acquire the ambiguity that it has always warranted.
Biology is just going to get more and more fun.
*First person to recite that pathetic “get your own dirt” joke is going to be rewarded with disemvowelment.
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 precisely alternating bands. In the picture above, for instance, one pair-rule gene, even-skipped, has been stained blue, and it is expressed in parasegment* 1, 3, 5, 7, etc. Another, fushi tarazu, has been stained brown, and this gene is turned on in parasegments 2, 4, 6, 8, etc.
No, actually they don’t — but they do have some proteins that are essential components of synapses, and it tells us something important about the evolution of the nervous system. A new paper by Sakarya et al. really isn’t particularly revolutionary, but it is very interesting, and it does confirm something many of us suspected.
The Newsweek cover story is on recent efforts to create life in the laboratory, and of course they call this “playing God”. Haven’t they got the message yet? “Playing God” is where you do absolutely nothing, take credit for other entities’ work, and don’t even exist — scientists don’t aspire to such a useless status. Besides, creating life is mundane chemistry, no supernatural powers required.
Here 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 asked me some years ago, I would have said it’s obvious: vertebrates must be more closely related to the cephalochordates—they have such similar post-cranial anatomies—while the urochordates are the weirdos, the most distant cousins of the group. Recent developments in molecular phylogenies, though, strongly suggest that appearances are deceiving and we vertebrates are more closely related to the urochordates than to the cephalochordates, implying that some interesting evolutionary phenomena must have been going on in the urochordates. We’d expect to see some conservation of developmental mechanisms because of their common ancestry, but the radical reorganization of their morphology suggests that there ought also be some significant divergence at a deep level. That makes the urochordates a particularly interesting group to examine.
Way 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 similarity in a flood of documented differences. Picking out a few superficial similarities and proposing that something just looks like it ought to be so is not a persuasive argument in science.
Something has changed in the almost 200 years since Geoffroy made his suggestion, though: there has been a new flood of molecular data that shows that Geoffroy was right. We’re finding that all animals seem to use the same early molecular signals to define the orientation of the body axis, and that the dorsal-ventral axis is defined by a molecule in the Bmp (Bone Morphogenetic Protein) family. In vertebrates, Bmp is high in concentration along the ventral side of the embryo, opposite the developing nervous system. In arthropods, Bmp (the homolog in insects is called decapentaplegic, or dpp) is high on the dorsal side, which is still opposite the nervous system. At this point, the question of whether the dorsal-ventral axis of the vertebrate and invertebrate body plans have a common origin and whether one is inverted relative to the other has been settled, and the answer is yes.
There is considerable interest in a recent paper in PNAS that purports to have found some rather substantial homologies in the proteins that make up the bacterial flagellum. That would be extremely interesting if it were true, but it looks like there are massive methodological problems in the work. Matzke has put up a preliminary criticism; the gang at PT are working on a much more detailed analysis, and if half of what I’m hearing about the paper is true … well, it’s going to be rather thoroughly sunk.
If you are arguing against ID’s favorite example, the flagellum, do not use the data in this paper. It’s about to go kablooieee. Sorry, everyone, but that self-correcting stuff is the way science is supposed to work (and letting error-filled papers make it to press is not supposed to happen, but it does all too often anyway.)
Nick has posted more info — it’s still not the complete argument, but the problem in the author’s interpretation is rather stark.
