Tuesday, April 07, 2009

lynn margulis - symbiogenesis

Scoop | Whereas speciation by accumulation of "random DNA mutations" has never been adequately documented, a plethora of high-quality scientific studies has unequivocally shown symbiogenesis to be at the basis of the origin of species and more inclusive taxa.

Members of at least two prokaryotic domains (a sulfidogenic archaebacterium, a sulfide-oxidizing motile eubacterium) merged in the origin of the earliest nucleated organisms to evolve in the mid-Proterozoic Eon (c. 1200 million years ago).

Such a heterotrophic, phagocytotic motile protoctist was ancestral to all subsequent eukaryotes (e.g., other protoctists, animals, fungi and plants).

The defining seme of eukaryosis, the membrane-bounded nucleus as a component of the karyomastigont, evolved as Thermoplasma-like archaebacteria and Perfilievia-Spirochaeta-like eubacteria symbiogenetically formed the amitochondriate LECA (the Last Eukaryotic Common Ancestor). Their co-descendants (that still thrive in organic-rich anoxic habitats) are amenable to study so that our videos of them will be shown here.

There are no missing links in our scenario. Contemporary photosynthetic (green) animals (e.g., Elysia viridis, Convoluta roscoffensis), nitrogen-fixing fungi (Geosiphon pyriforme), cellulose digesting animals (cows, Mastotermes darwiniensis termites) and plants (Gunnera manicata) make us virtually certain that Boris Mikhailovich Kozo-Polyansky's (1890-1957) analysis (Symbiogenesis: A New Principle of Evolution, 1924) was and still is correct.

Symbiogenesis accounts for the origin of hereditary variation that is maintained and perpetuated by Charles Darwin's natural selective limitations to reaching the omnipresent biotic potential characteristics of any species.


Cgoslingpbc said...

Endosymbiosis and Symbiogenesis are fantastic additions to the concept of evolution. Darwin would have been delighted.

ken said...

Postmodern synthesis is what the other biologist finally called this paper when they discussed it. Think Lynn now might be 20th century thinking now.


CNu said...

Then you would plainly be mistaken. From the articleHorizontal gene transfer was assumed to be uncommon, as the process of genes entering a new genome is counter to the idea of a sleek and well adapted genome. (B) After analyzing the genomes of many prokaryotes, biologists recognized that horizontal gene transfer may be a common event. Furthermore, prokaryote species trees may be viewed as a patchwork of gene trees with varying levels of congruence. A similarly hierarchical view of eukaryote evolution has been articulated by Maddison [15], except that differential coalescent times – usually not horizontal transfer – is the primary mechanism used to explain incongruence of gene and species trees.

Similarly, modernist preconceptions led some to discount the importance of endosymbioses in the origins of new life forms, like eukaryotes. Broad theories of endosymbiotic origins for species had been suggested in the late 19th and early 20th Centuries [7], but were ignored save for a few well-established cases like lichens. By the 1980s, the evidence for symbiogenesis in major cell biological events was voluminous [13,14].

Even systematics has had to abandon many strictures that were part of the Modern Synthesis. If species are the durable unit of biology, and if natural selection quickly molds genes to current utility, then most genes should diverge at the time of speciation events, given views like Mayr's. Here again, analyses of newly abundant sequence data in the late 20th Century showed that rather than a highly congruent coalescence of genes at the times of speciation events, the coalescence times of alleles among species are highly variable. As such, species trees and gene trees often cannot be equated [15,16].

ken said...

Well yes true, but I think what I was noticing is that we have moved from any one method or vehicle to get from one complexity to another to instead many. As was said under the new rules for biology:

We should no longer assume that a biological research problem can be satisfactorily solved using the intellectual tools from only one biological discipline. This might be the case, but it is likely that most valid one-discipline solutions are the 'low-hanging fruit' already picked by 20th Century biology.

And later under "Nothing New"

"Present-day biologists are instead dealing with the C-value paradox in terms of the evolution of non-coding DNA, the proliferation of transposable elements, and kindred phenomena. This does not imply that evolutionary theory simply no longer applies. Instead, new evolutionary theories have been developed, such as Lynch and Conery's theory of reduced effective population size leading to less efficient selection against the proliferation of non-essential, even deleterious, DNA sequences, and thus greatly expanded genome sizes in endemic species with small population sizes [83,84]. It is not our concern to argue for or against this particular theory, only to point out that this scientific debate was not a live issue for biologists in 1970. And it certainly wasn't an obvious corollary of the systems biology perspective then extant, either.

The fundamental landscape of biology is undergoing a major upheaval, much as it did in the first decades of the 20th Century [1]. This upheaval will take time to fully reveal its implications. The sequencing of several important eukaryotic genomes around the year 2000 was no more an instant transformation of biology than the re-discovery of Mendel was in 1900. Decades are required to change the foundations of a scientific field as complex as biology."

So it wasn't that I was saying Lynn was being replaced, but now we are moving to multiple explanations. I took note of and interview with Lynn here:


I don't think I have ever heard another admit so much in this question and answer:

Interviewer: "Some of your criticisms of natural selection sound a lot like those ofMichael Behe, one of the most famous proponents of “intelligent design,” and yet you have debated Behe. What is the difference between your views?

Margulis: "The critics, including the creationist critics, are right about their criticism. It’s just that they’ve got nothing to offer but intelligent design or “God did it.” They have no alternatives that are scientific."

I would have wished a follow up question to be: If God ended up being the right answer, could God also be a scientific alternative?