posted 03. September 2003 01:58                   

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I would emphasize the importance of including examples from the developmental genetics approach when discussing evolution in public. In addition to being easier to understand than the population genetic approach to teaching evolution, the developmental approach might have other advantages. First, the developmental genetic approach uses examples that everyone can understand from visual experience. Second, evolution at the level of developmental regulatory genes might be the main source of variation. In humans that animal for which variations have been catalogued most carefully), genes are heterozygous at more functional cis-regulatory sites (gt 16,000) than at exon sites ( lt 13,000). Ordinary small-scale mutations contribute to large variations in transcription rates across the genome and so to human variation57. Third, these examples address the questions of evolutionary novelty that creationists say cannot be explained by evolution — how insects have fewer legs than centipedes, how snakes lost their legs, how birds got feathers and ducks got their webbed feet.We are therefore able to show where creationists are wrong and how their ideas about homology and morphological novelties are out of date. If the processes of evolution were viewed solely from the population genetic perspective, it would appear very difficult to explain the origins of feathers, teeth and eyes. They seem to be (in the words of the creationists) "irreducibly complex"6. However,when the perspectives of embryonic induction and developmental genetics are added, these novelties become explainable, at least in outline, if not yet in detail. Such information is crucial if we are to counter the distortions of science by creationists58.

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posted 05. September 2003 00:25                   

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So I am especially appreciative of speaking here today about the role that developmental biology can play in education, especially educating our undergraduates and high school students about evolution. I will contend that we can teach evolution more effectively using developmental genetics than population genetics. Both are required for any theory of evolution, but I propose that students will learn the principles of evolution better from examples of animal development than they can from the mathematics of natural and laboratory populations. The examples I will use are perhaps not the ones others would use. I will be using examples that my undergraduates would appreciate--which means I will mainly be talking about vertebrates and insects. My apologies in advance to the allies of all other clades.

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When biologists are asked to discuss the evidence for evolution at public forums, they usually use well-established microevolutionary examples. Although these examples show the efficacy of evolution within species, they often leave audiences susceptable to the arguments of creationists who deny that evolution can create new structures and species. Recent studies from evolutionary developmental biology are beginning to provide case studies that specifically address
these concerns. This perspective presents some of this new evidence and provides a framework in which to explain homology and phylogeny to such audiences.

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posted 05. September 2003 12:09                   

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These footnotes deal specifically with Creationism and how evolutionary developmental biology can confront its claims.

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posted 08. September 2003 21:01                   

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Despite increasing recognition that genetic networks have been “rewired” over the course of evolution (Szathmary 2001; Wray 2001), that “key” genes can often be knocked out of complex organisms with little or no phenotypic consequence (Shastry 1995), and that the same genetic manipulation may give rise to animals exhibiting profoundly different phenotypes when present on diverse genetic backgrounds (Sigmund 2000)...In the absence of a theory for origination of morphological traits other than mutation-based incremental trial-and-error, there is no alternative but to reject the idea of rapid, large scale organizational innovations, and search for functional significance in every molecular detail. This is the “reverse engineering” approach that dominates contemporary developmental biology. But if, as seems likely, organisms were originally Proteus-like, subject to molding by externally-conditioned, self organizing, epigenetic processes, subsequent molecular evolution would have had primarily restricting, consolidating, and reinforcing roles. Deconstructing modern development would thus require testing hypotheses about originating processes and evolutionary trajectories and not confine itself solely to contemporaneous functional analysis.

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Because a gene operates to facilitate an outgrowth that becomes a limb in several different taxa of animals thus does not mean that legs evolved only once, much less that all legs are homologous. Rather it indicates that genes and gene cascades/networks have been recruited convergently as organizers of limb devleopment.

Origination of Organismal Forms.

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posted 09. September 2003 00:58                   

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Whiting and his team made the discovery while preparing a family tree of walking stick insects. They suspect that like other insects walking sticks lost their wings and ability to fly so they could better adapt to their environment.
A lack of wings in walking sticks probably increased their ability to blend into their surroundings to protect themselves from predators.

"At least 50 million years later, for some reasons, it was to their advantage to have some of the species become winged again," he added. Scientists had believed that once a trait was lost it was gone forever because the genes needed to create it would be changed.

Whiting said the genetic instructions to produce wings and legs are probably related and can probably be switched on and off over millions of years. He suspects re-evolution may have occurred in other species including cockroaches and different insects and possibly other animals.

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Researchers assumed wings could not come back once lost as the genes needed to create them would mutate beyond repair once the wings disappeared. But Whiting says there is evidence from the fruit fly Drosophila that the same genes contain instructions for forming wings and legs.
If the same were true for stick insects, there would be an evolutionary pressure to stop wing genes from mutating, even in the insects that did not have wings. Those genes could then be turned back on in the future.

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posted 09. September 2003 17:35                   

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I am not sure how you reached this conclusion. Could you give some details? As I understand Whiting suggests stick insects evolved from cockroaches who have wings.

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Stick insects come in two flavors -- winged and wingless. The study reports that the earliest stick insects had no wings. Whiting said this posed a problem because stick insects descended from cockroaches, which have wings. Because of this, primitive stick insects should have had wings, the researchers theorized.

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Some insects lost their wings, only to regain them at a later moment. Fascinating how hox genes can re-express themselves.

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but what I find interesting about Ubx is that it was co-opted in derived forms. Ancient insects don't even have wings. Timema, for example, is the most primitive living stick insect lineage and it is wingless. Data from Whiting suggests to me that wings appeared in 6 lineages convergently.

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Because a gene operates to facilitate an outgrowth that becomes a limb in several different taxa of animals thus does not mean that legs evolved only once, much less that all legs are homologous. Rather it indicates that genes and gene cascades/networks have been recruited convergently as organizers of limb devleopment.

Origination of Organismal Forms.

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I am not sure how this relates to front loading though. I would hope Nelson could expand on this in some detail. Was front loading supposed to remove the wings on certain walking stick insects or have them re-evolve?

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posted 09. September 2003 23:42                   

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These results support the hypothesis that the ancestral condition in Phasmatodea is wingless, that the first six basal phasmid lineages are entirely wingless, and that fully developed wings were derived later in phasmid evolution, on as many as four occasions.

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The detailed homology in wing features shared
among phasmids and other insects suggests that wings did not reevolve de novo in phasmids, but are rather a re-expression of the basic insect wing which was lost in ancestral stick insects.

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Therefore it is not surprising that the basic genetic instructions for wing formation are conserved in wingless insects, because similar instructions are required to form legs, and probably other critical structures16.

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posted 09. September 2003 23:58                   

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The article may have misled you, the phasmid evolved from an ancestral form which does have wings. What happened is that the ancestor of the Phasmids did not have wings and that some gained wings. SInce you are quoting from newspapers, I presume you do not have access to the original paper which would have resolve much of this easily.

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Whiting said he expects to find more examples of re-evolution in other insect groups, such as cockroaches.

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So in short, ancestral stick insects lost the ability to form wings but rather than evolving de-novo, the genes responsible for wings were re-expressed in some later descendants.

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posted 10. September 2003 00:16                   

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"An alternative explanation for their data is that the loss of wings is much more likely than the gain of wings and many different lineages lost their wings independently," Norton said.

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Have you seen the cladistic analysis they did? Figures 2 and 3 may be helpful to you.

posted 10. September 2003 00:19                   

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Your comments suggested to me that you thought that the article stated that the walking stick insects ancestor was flightless.

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Ancient insects don't even have wings. Timema, for example, is the most primitive living stick insect lineage and it is wingless. Data from Whiting suggests to me that wings appeared in 6 lineages convergently.

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posted 10. September 2003 00:28                   

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The latter. Some examples from Michael Denton's book seem relevant. For example with some marsupial and placental mammals, the tape of evolution seems to have been re-run, many placental mammals have marsupial counter-parts, and that both groups have done so independantly.

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The entire nucleotide sequence of the mitochondrial genome of the American opossum, Didelphis virginiana, was determined. Two major features distinguish this genome from those of other mammals. First, five tRNA genes around the origin of light strand replication are rearranged. Second, the anticodon of tRNA(Asp) is posttranscriptionally changed by an RNA editing process such that its coding capacity is altered. When the complete protein-coding region of the mitochondrial genome is used as an outgroup for placental mammals it can be shown that rodents represent an earlier branch among placental mammals than primates and artiodactyls and that artiodactyls share a common ancestor with carnivores. The overall rates of evolution of most of the mitochondrial genome of placentals are clock-like. Furthermore, the data indicate that the lineages leading to the mouse and rat may have diverged from each other as much as 35 million years ago.

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Also, no fossil of our species has been found more than about 160,000 years old, and the estimate of our speciation is less than 200,000 years from a very small population size. Since then it seems as though both hominids and humans evolved independantly the ability of tool-making/technological innovation, burying the dead, wearing clothes, maybe even religious belief. As it may be with the situation with legs, could this type of intelligence have evolved via frontloading?

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posted 10. September 2003 00:42                   

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And yet all this 'front loading' may be explained by hox genes for instance.

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Also, that the same hox gene can intervene in many different patterning processes (in shrimps for example). Different organisms seem to have co-opted genes for purposes specific to it's clade.

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Without any substantial explanation of front loading it seems to be hard to see how such an idea may be explored in a scientifically fruitful manner but I am surely eager to see you develop one.

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I find the concept of front loading a somewhat vague concept to describe what we do not know and thus treat as initial or boundary conditions.

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