Was Lamarck right?

There are three ways in which bacteria can gain genetic material that are not related to mutation: transformation, tranduction and conjugation. Transformation — when bits of dead bacterial DNA are taken up by others directly from the environment; transduction — when a bateriophage accidently packages a donor cell’s DNA (rather than its own) and transfers it to a new cell; and conjugation, which is direct transfer of genetic material (usually on plasmids) from one bacteria to another.Bacteria and other single celled beasties can be pretty promiscuous. Both transformation and especially conjugation can literally create a new clonal lineage with one or more completely novel characteristics in one go. In essence, it IS the inheritance of acquired characteristics a la Lamarck. It’s sort of like if a seagull was able to pass genetic material directly to a mouse, and create a flying, feathered rodent in one generation.Where Margulis is overstating the case is her claim that:a) this falsifies or calls into question neodarwinism (i.e., role of mutation and ns in evolution): It doesn’t — bacteria and their ilk are something of a special case in a lot of ways, not least of which is the difficulty in identifying species because of the lack of reproductive barriers and the fact that they are clonal. It has been recognized for quite a while that bacteria and the biological species concept don’t mix. This tends to be one of Margulis’ favorite strawman arguments. OTOH, it does have substantial implications for the very roots of the mangrove of life and may render moot the search for the elusive LUCA — not because this hypothetical organism doesn’t exist, but rather its trail may be impossible to untangle from the web of bacterial interactions.b) there is sufficient evidence that genomic fusion between single-celled critters and multicellular critters has had a significant impact on evolution. This is an area where there is outstanding room for future research. The role of retroviral insertions (as Mammuthus mentioned) for instance and their effect in altering the genotype or phenotype of a complex organisms is relatively undeveloped — although there’s a good bit of work on-going. I think it’s too early to state what role they play — Mammuthus probably has a zillion papers under his thumb at this very moment OTOH, even if there is a role, IMO it would be merely in supplementing random mutation in creating genetic novelty, and would not refute or replace the critical role of natural selection.A related area that I find particularly interesting — and with more empirical support that what Margulis is proposing, but still a very new area of research - is the role of parasitism in driving evolution. I know you like well-written popsci books, and if you’re interested in a contrast to Margulis, I think you’d find Carl Zimmer’s Parasite Rex (Touchstone/Simon & Schuster, 2001) fascinating. (*Q thus pays Tamara back for forcing him to buy Acquiring Genomes).

Hi Denesha. Great questions! I'm not a microbiologist, so I may be a bit off here. However, I think the point I was trying to get across is that the part of Lamarck's theories concerning "inheritance of acquired characteristics" is - at least by analogy - more or less what can happen in clonal (whether unicellular or metazoan) lineages. I don't consider it a violation of neodarwinism. It's still natural selection and descent with modification. It messes up the biological species concept is all, and most microbiologists I've talked to simply state that the BSE doesn't apply at the unicellular level (i.e., begging the question in a way ). Since the BSE isn't really much more than a very handy "rule of thumb" anyway, I don't think clonal lineages pose any problem for evolutionary theory. Clones simply have some different reproduction options. My understanding is that bacterial lineages for instance are classified by percent relatedness. If DNA analysis shows X% difference (I can't remember what the percent is, but I want to say <75% similarity which is probably wrong), then the organisms are classified as different "species", although lineage is probably a better term for it.As to "potential unified mechanism", if I understand what you're suggesting, I would think this would be the "holy grail" of biology. It would be an incredible breakthrough - along the lines of Einstein's relativity theory - if such a unified theory could be developed. Way more brilliant minds than mine (not saying much here) have pondered the problem, promulgated fascinating theories, and come up short when the details were examined. I think the problem derives from the "nature of the beast". Organisms simply don't lend themselves to simple rules. I mean, in physics, an electron is an electron is an electron whether it's part of a hydrogen atom or a nobelium atom. It's one example of an identical class of components whose properties are identical. Compare that to an individual biological organism - each one is unique and different from all others, even if it's a member of the same population or species. Generalizing on something like that is, hmmm, problematic in my opinion. I don't really think the rules are different. I think it would be better said that bacteria have some additional rules and complications that need to be taken into consideration. As to your question, I think the significant impact would be on the very root of the tree of life, not on the course of evolution per se. Unless Margulis for instance is shown to be substantially correct, and symbiosis is shown to be a more important force than natural selection and competition in the evolution of the majority of organisms - which would cause us some major re-thinking of how diversity and evolution played out.

LUCA = "last universal common ancestor"This is the elusive "first organism" - not first replicator - from which all cellular organisms on the planet descend. Our most ancient ancestor. Here's a nice on-line article which reviews the topic: My Name Is LUCA. BTW, you might enjoy that website a lot. Actionbioscience.org is a cross between pop sci and peer-reviewed, and contains articles and essays by many of the "big names" in biology including Eldredge, Simberloff, Wilson, etc.

You're probably asking the wrong guy. If you want my opinion - then yes, I think the ultimate root is more like a bush than a tree. Or, if you want to extend the tree analogy, it's like a tree with a whole root system.Here are a couple of articles that might help explain why I think that:Gogarten JP, Doolittle WF, Lawrence JG, 2002, "Prokaryotic Evolution in Light of Gene Transfer", MolBioEvo 19:2226-2238

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Accumulating prokaryotic gene and genome sequences reveal that the exchange of genetic information through both homology-dependent recombination and horizontal (lateral) gene transfer (HGT) is far more important, in quantity and quality, than hitherto imagined. The traditional view, that prokaryotic evolution can be understood primarily in terms of clonal divergence and periodic selection, must be augmented to embrace gene exchange as a creative force, itself responsible for much of the pattern of similarities and differences we see between prokaryotic microbes. Rather than replacing periodic selection on genetic diversity, gene loss, and other chromosomal alterations as important players in adaptive evolution, gene exchange acts in concert with these processes to provide a rich explanatory paradigmsome of whose implications we explore here. In particular, we discuss (1) the role of recombination and HGT in giving phenotypic "coherence" to prokaryotic taxa at all levels of inclusiveness, (2) the implications of these processes for the reconstruction and meaning of "phylogeny," and (3) new views of prokaryotic adaptation and diversification based on gene acquisition and exchange.

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And of course Carl Woese's work (who's one of the first proponents of the theory, along with Gould), like Woese C, 2000, "Interpreting the universal phylogenetic tree", PNAS 97:8392-8396.

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The universal phylogenetic tree not only spans all extant life, but its root and earliest branchings represent stages in the evolutionary process before modern cell types had come into being. The evolution of the cell is an interplay between vertically derived and horizontally acquired variation. Primitive cellular entities were necessarily simpler and more modular in design than are modern cells. Consequently, horizontal gene transfer early on was pervasive, dominating the evolutionary dynamic. The root of the universal phylogenetic tree represents the first stage in cellular evolution when the evolving cell became sufficiently integrated and stable to the erosive effects of horizontal gene transfer that true organismal lineages could exist.

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It probably looks more like this: Or maybe, this: That's my opinion, for what it's worth. Drat those pesky prokaryotes and their failure to develop cam corders.

I actually prefer the single cell => colonial organism => metazoan hypothesis. If you look at colonial algae like Volvox spp, you can see what might be an illustrative "pathway" for early metazoan evolution.Volvox are eukaryotes that form spherical colonies embedded in a gelatinous ball in ponds of about 1000 cells. Each member is a fully formed, complete, and distinct organism. They all have flagella, all have their own chloroplasts, and all have their own opsin eyespots. What's interesting about them, is that although all the flagella are beating about, the colony itself seems to have a "front" and "rear". At the front, the organisms have larger eyespots, and the rear group do most of the propelling for the colony. IOW, it moves as a group in a coordinated fashion. In addition, only the rearmost seem to reproduce. Some species even have the cells linked by cytoplasmic threads. To me, this looks like an example of very early cell differentiation - a key element in metazoa.From something like Volvox it's only a short step to something like a choanoflagellate, for example. And from there, it's an even shorter step to multicellular, highly diversified organisms like the Portuguese Man-o-War (Physalia physalis), which is a colonial jelly-fish like organism composed of four distinct organisms, each one specialized for a particular function within the colony.I don't disagree with you that there's a great deal of evidence for symbiosis down at this level - chloroplasts, mitochondria, and possibly other sub-cellular structures appear to have been originally free-living organisms in their own right that got coopted. On the other hand, I don't think that two disparate organisms joined together to form the first metazoan. I'm of course open to correction.

I think we're getting off topic (Q expects a hammer blow from the forum Supreme Beings at any moment). However, a quick note before we get ADMINmonished: The Woese article uses a tree analogy in the form of early life = tangled roots --> cellular life = trunk --> more complex cellular life = the three great branches (like the top pic in my post). I think this is what you mean. Margulis, among a few others, doesn't agree, and basically states that the situation stayed complicated until much more recent times, even after the rise of metazoans (closer to the bottom pic). She even goes so far as to state that metazoans themselves are subject to this type of genome exchange and fusion. That's the bit I find hard to swallow, btw. The first article I cited is way better than the abstract, so if you can get ahold of the full article, it's worth a read.