Front-loading and the nervous system
by MikeGeneThe front-loading perspective on evolution continues to spread and deepen. From, The origin of the brain lies in a worm:
The rise of the central nervous system [CNS] in animal evolution has puzzled scientists for centuries. Vertebrates, insects and worms evolved from the same ancestor, but their CNSs are different and were thought to have evolved only after their lineages had split during evolution. Researchers from the European Molecular Biology Laboratory [EMBL] in Heidelberg now reveal that the vertebrate nervous system is probably much older than expected. The study, which is published in the current issue of Cell, suggests that the last common ancestor of vertebrates, insects and worms already had a centralised nervous system resembling that of vertebrates today.
and
"Our findings were overwhelming," says Alexandru Denes, who carried out the research in Arendt's lab. "The molecular anatomy of the developing CNS turned out to be virtually the same in vertebrates and Platynereis. Corresponding regions give rise to neuron types with similar molecular fingerprints and these neurons also go on to form the same neural structures in annelid worm and vertebrate."
What is so encouraging about this type of finding is that it is not unique. On the contrary, there seems to be a growing pattern of scientists finding that molecules and systems are "probably much older than expected." But what has been behind all these failed expectations? Perhaps the view of simple beginnings has played a role.
April 21st, 2007 at 1:13 pm
Why hasn't this "living fossil" evolved? If natural selection works on all organisms, shouldn't it work on Platynereis as well? As far as I'm concerned, this article does not only give fodder to the front loading idea. It also undermines natual selection. How do the Darwinian votaries explain inconsistencies like this?
Comment by AnaxagorasRules — April 21, 2007 @ 1:13 pm
April 21st, 2007 at 1:22 pm
I believe their answer would rest in the part about "it still lives in the same environment as the last common ancestors used to and has preserved …"
Natural selection does not always imply change. Strictly speaking, it only means that changes relatively unsuited to an environment are weeded out in preference to those that are best suited. No change in the environment might mean that you have only stasis.
That much is not incorrect. Where Darwinians go badly off the rails is when they attribute to Natural Selection a mystical ability to create anything new. NS creates nothing at all. It can only arbitrate over whatever happens to come along accidentally by random variations. NS is purely subtractive — think hedge trimmer. It never adds anything at all.
Comment by eric — April 21, 2007 @ 1:22 pm
April 21st, 2007 at 1:48 pm
Anaxagoras Rules asks:
Don't let the term "living fossil" mislead you. The article states that Platynereis "has preserved many ancestral features," which is a far cry from claiming that it has remained unchanged over time.
Same deal with the coelacanth. It's widely regarded as a "living fossil", but that doesn't mean that living coelacanths are identical to fossil coelacanths.
Comment by keiths — April 21, 2007 @ 1:48 pm
April 21st, 2007 at 1:48 pm
Natural selection (NS) *is* creative in the sense that it changes the composition of a population. The distributions of traits before and after selection differ. You could say that part of the distribution before selection is removed by selection, almost like a sculptur removes parts of a chunk of marble in order to create a sculpture. So, a good case can be made that NS, all by itself, is a creative process. Of course, long-term evolution requires some additional ingredients such as genetic variation underlying trait variation, and new genetic variants arising by mutation of old ones.
Comment by Raevmo — April 21, 2007 @ 1:48 pm
April 21st, 2007 at 2:11 pm
FYI - for anyone who wants to read the article, the journal has it available as a free download and also has a place to leave comments on it.
Comment by johnnyb — April 21, 2007 @ 2:11 pm
April 21st, 2007 at 2:42 pm
The actual documentation for this is largely circumstantial. Unicellular organisms are the best examples but what we observe, as opposed to what we theorize, is a genomic flux that responds to environmental stimulii. Allele frequencies change but are apt to revert back to original allele frequencies when conditions change back to their original state. What we do not witness is the type of IC formations that require multiple mutations of different genes encoding distinct functions. Those changes are reasoned by extrapolation.
Comment by Bradford — April 21, 2007 @ 2:42 pm
April 21st, 2007 at 3:00 pm
Hi, Keiths,
The coelacanth is much younger than Platynereis, which puts Platynereis in a different ballpark. The inconsistency is that, if the common ancestor (Urbilateria) was the substratum from which all the vertebrates came from (and not far removed from Platynereis, which the article implies), then Platynereis is an obvious oddity, in that it did not vary like the other vertebrates. Did Platynereis not have predators? Did the environment of Platyneries remain relatively the same for eons? Is Platynereis found in more than one location? It does not make sense that there is such a discrepancy between the rates of change of Platynereis and the other offshoots of Urbilateria, not when when such huge timeframes are involved. It is this sort of glossing over that is deleterious to science's and, particularly, biology's credibility. Or, to be more correct, to the credibility of biology's practictioners who advocate natural selection as the sole cause in evolution.
Comment by AnaxagorasRules — April 21, 2007 @ 3:00 pm
April 21st, 2007 at 6:20 pm
More about Platyneriis.
Comment by Krauze — April 21, 2007 @ 6:20 pm
April 21st, 2007 at 9:42 pm
How is it front loading? Is it your claim that the ancestor worms had all the "instructions" on how to make a platypus nervous system? It would be easy to check, comparing the platypus to the worm . . .
AnaxagorasRules, if you are the descendant of your parents, why did your parents survive after your birth? If humans in America are descendants of humans in Europe, Africa and Asia, why are there still humans in Europe, Africa and Asia?
This bizarre post, attempting to hitchhike on a science article, is a spotlight on why ID cannot be science, if one bothers to look.
Comment by edarrell — April 21, 2007 @ 9:42 pm
April 21st, 2007 at 10:14 pm
Hi, edarrell,
That has nothing to do with the point I brought up, which is why was there such a disparate rate of evolutionary change between Platynereis and the other offshoots from Urbilateria (the common ancestor)? How does natural selection explain that?
Comment by AnaxagorasRules — April 21, 2007 @ 10:14 pm
April 21st, 2007 at 11:29 pm
Your question, "why hasn't this living fossil evolved," is the point I was responding to, AR. You're recycling old canardly creationist stuff. Useful stuff should be recycled, harmful stuff should be discarded.
Different conditions make different rates of change. Mutation rates may be stable, while selection rates differ, which produces one way to track back to see how long ago splits between species occurred.
Shy would there not be disparity in the rates of change? I'm not sure why anyone thinks that's an issue, nor why you wouldn't have noticed extensive discussion about why evolution rates differ, in the literature.
Were one a serious seeker of knowledge about evolution and our ancestors among the worms, one might peruse some serious discussion of such issues, such as at the Howard Hughes Medical Institute site: http://www.hhmi.org/geneswesha...
Comment by edarrell — April 21, 2007 @ 11:29 pm
April 21st, 2007 at 11:29 pm
Shoulda been "Why would there not be disparity . . ."
Comment by edarrell — April 21, 2007 @ 11:29 pm
April 21st, 2007 at 11:48 pm
Edarrell:
No, I did not make that claim nor did I say this is front-loading. I noted this as an example of the widening and deepening perspective of front-loading.
I don't care if ID is labeled science nor do I care what you think. What matters to me is that when I first contemplated FLE, it was a wild guess. Yet as the years go by, and the data come in, the plausibility of FLE continues to grow and I am continually encouraged. Again, consider what the above article says:
This is what conventional theory taught. But in come new data that "now reveal that the vertebrate nervous system is probably much older than expected." This is the type of thing FLE predicts and the type of thing we see with many molecules/systems. "Older than expected" means closer to the design event. That the last common ancestor of vertebrates, insects and worms already had a centralised nervous system resembling that of vertebrates today is something that is quite friendly to FLE. Yet the original view could have turned out to be correct.
Comment by MikeGene — April 21, 2007 @ 11:48 pm
April 22nd, 2007 at 12:40 am
MG:
edarrell's skepticism afforded the opportunity to emphasize a valid point. If ID is to move in the direction of widespread scientific acceptance it needs to have predictive utility. Mike's subtle point is consistent with the FL concept.
Comment by Bradford — April 22, 2007 @ 12:40 am
April 22nd, 2007 at 1:19 pm
Hi, edarrell,
So mutation rates are determined by something other than natural selection? No argument here. This was the point of my comment. The environment is not the only factor. Natural selection seems to be at best only a partial explanation for evolution. The cell is an organism. How does natural selection determine a cell's activities? What predators inside the cell are forcing it to mutate? Natural selection is a model that might be useful on nature walks, to help understand the logic behind some of the patterns that we see, but I think that science has already moved past natural selection. At the molecular level, it seems that a new model is taking shape, and in the search for function and purpose, I doubt if randomness is the holy grail that is being sought. In the article that MikeGene linked to, at the very end of it, the scientist passed the onus of explanation to the evolutionary biologists. Talk about passing a football.
Comment by AnaxagorasRules — April 22, 2007 @ 1:19 pm
April 22nd, 2007 at 3:30 pm
AnaxagorasRules
As the writer of "Evolution of eyes and photoreceptor cell types" and other related papers, Detlev Arendt is clearly an evolutionary biologist. So when he refers to, "the next exciting questions for evolutionary biologists," he is talking about his peers within his own field of study. Looking more closely at this paper from 2003, Arendt is proposing a testable hypothesis and research program within the paradigm of the Theory of Evolution, and his more recent work confirms his approach.
Mike Gene
The origin of primitive structures is difficult to discern. The further back into time scientists peer, the less certain their data. We have several limbs of the phylogenetic tree that have nervous systems, and these nervous systems can appear very different. So it might seem on first glance that they arose independently. However, a more refined observation has determined (and the data seems to support the paper) that the origin of the nervous systems is pushed farther back up the tree, to the common bilaterate ancestor. There is nothing about this that undermines the phylogenetic tree, and indeed, is additional confirming evidence of common descent of the lineages.
We *expect* that many structures have even more distant roots. But determining that requires data, and new techniques in molecular biology now make such data available.
Bradford
There's the rub. Arendt and others use the Theory of Evolution to produce fecund hypotheses to help understand the history of that evolution; while Intelligent Design offers no specific observations that can provide empirical support for its assertions.
Comment by Zachriel — April 22, 2007 @ 3:30 pm
April 22nd, 2007 at 3:51 pm
Zachriel,
Where did you get the idea that Mike wants to "undermine the phylogenetic tree"
Comment by Krauze — April 22, 2007 @ 3:51 pm
April 22nd, 2007 at 4:08 pm
There is not necessarily a conflict between striving toward understanding of evolution and positing indicators of intelligent design while doing so. I believe there are specific observations related to the evolution of particular biological systems that would lend support for design. Nervous systems might not be the best candiadtes. Supporting systems of some of life's basic functions (DNA and protein synthesis) could be more fruitful indicators of design.
Comment by Bradford — April 22, 2007 @ 4:08 pm
April 22nd, 2007 at 4:37 pm
Okay, I'll concede that. When he didn't use the "we" to reference the evolutionary biologists, I took that to mean that his team was essentially composed of microbiologists.
I still don't see how natural selection makes any sense at the cellular level. To me, the concept of natural selection is an emergent property that tries to explain the natural world. The factors are the environment, time, predation, and randomness. At the cellular level, there are like and unlike charges that cause chains of molecules to come into being, with their shapes determining their functions. There needs to be a new model to explain what is happening at that scale.
Comment by AnaxagorasRules — April 22, 2007 @ 4:37 pm
April 22nd, 2007 at 6:31 pm
Krauze:
According to the ID = Creationism meme, the critic thinks he/she need only cast this is an pro/anti-evolution issue to score non-telic points. But evidence for common descent is not evidence for the non-teleological perspective.
Comment by MikeGene — April 22, 2007 @ 6:31 pm
April 22nd, 2007 at 7:09 pm
Bradford
That there could *conceivably* be indicators of intelligent design is not to say there are indicators of intelligent design.
AnaxagorasRules
Natural selection meaning environmental selection. But the environment is often simply the access to resources. Better replicators will tend to prevail upon the supply of resources, regardless of whether it is vertical or horizontal evolution.
AnaxagorasRules
However, there is the interregnum between chemistry and organisms where natural selection may not explain the process.
MikeGene
I never made that conflation. I assumed from context that you accept common descent, but claim that there is intelligent agency in biological descent via a vaguely defined mechanism you refer to as "front loading".
However, you did ask, "But what has been behind all these failed expectations?" These expectations are drawn upon the specifics of the phylogenetic tree, and as these expectations were not universally shared, and as the surprisal is well within the existing paradigm, that made the point relevant to your question "” or so I thought. (I don't "score points".)
Comment by Zachriel — April 22, 2007 @ 7:09 pm