On Symbiogenesis

I recently finished reading a wholly remarkable book.

It is one of the most fascinating and dangerous books I've ever read, and although there is a lot of time to come in this century, it may prove to be one of the seminal classics defining the 21st century: Acquiring Genomes: A Theory of the Origins of Species by Lynn Margulis and Dorion Sagan (Basic Books: 2002).

I've been itching to comment on this book since I started this Web log, but I wanted to finish it first. Every thinking person should read this book.

Why the high praise? Several reasons. Margulis and Sagan, a mother and son scientist team, outline a theory to explain the source of heritable variation and to explain how speciation, the evolution of new species from existing species, occurs.

Students of the liberal arts may at first suspect foul play here—for we been taught that these are no longer valid questions. We have been taught that heritable variation mostly stems from random mutations, with phenotypic utility or not, which accumulate over time in those organisms selected by nature to survive and successfully reproduce. We have been taught that speciation occurs when populations of species, often if isolated geographically or at least reproductively, undergo genetic drift as a result from specific environmental circumstances which result, over time, in segregated populations which can no longer viably reproduce fertile offspring because they are no longer genetically similar enough. (I recall a quiz in a human origins college course in which we were asked to describe how genetic drift as a result of geographic isolation might result in the evolution of two distinct species from one founding population. With deference and respect to Professor Axelrod, who administered the quiz, and with my apologies if I am failing to remember the question correctly, I have to admit there was a tiny little bell in the back of my head that sounded even at the time—while speciation by geographic isolation seemed logical enough (Madagascan lemurs come to mind as stereotypes easily lumped into this category without sufficient follow-up thought as to the actual hows), I wondered then about how many Madagascar-like isolated environments would be required to fill the planet with the biodiversity it has now and has had in the past. I wondered, also, why this was even a question worthy of asking undergraduates because on the one hand it seemed so plain that speciation must occur in such a way (having denounced Lamarck conceptually in high school biology, how else could it?) and on the other, it seemed awfully curious why we didn't have current-day examples of isolated populations resulting in observable speciation over the past 200 years, while biological science in some form has been watching (dog breeds and pea plants being examples of variation within a species rather than development of different species—as popular culture will inform us, a Doberman can still hump a Chihuahua).* It seemed, then, that speciation was a thing of the past, that we couldn't put our finger on recent examples of organisms directly traced to their historical ancestor. It seemed that speciation was observable only across geological timescales, and, as it is impressive and daunting to think across geological timescales, I didn't rigorously question this premise as I now feel empowered to, as I am outside the academic establishment.**

What Margulis and Sagan say is this: "We do not deny the importance of mutations. Rather we insist that random mutation, a small part of the evolutionary saga, has been dogmatically overemphasized. The much larger part of the story of evolutionary innovation, the symbiotic joining of organisms (similar, if we extend the printing analogy, to the fusion of texts in plagiarism or anthologies) from different lineages, has systematically been ignored by self-proclaimed evolutionary biologists."

They link their idea, dubbed symbiogenesis, with the punctuated equilibrium concept popularized by Stephen Jay Gould.***

I want to quote a bit more from them before continuing the discussion as to why I feel their thesis is highly significant not only within biology but also in various wider human spheres of thought and action.

Margulis and Sagan: "No evidence in the vast literature of heredity change shows unambiguous evidence that random mutation itself, even with geographical isolation of populations, leads to speciation."

I haven't searched the literature myself, but I'm accepting their qualification about "unambiguous" evidence and linking their claim to my misgivings about those Madagascan lemurs (and even, as the authors discuss, Darwin's famous Galapagos finches, which are heavily studied today and observed to undergo significant genetic drift within species but have not demonstrated actual speciation despite significant environmental shifts).

One more direct quote from the book to set the stage. This one describes what they advance as the primary mode of speciation, symbiogenesis, which highlights the role of bacteria and other microbes in the totality of the evolutionary narrative of all life.

Margulis and Sagan: "From different vantages this poorly known idea can be gleaned: The agents of evolutionary change tend to be fully alive organisms, microbes, and their ecological relations, not just the random mutations these microbes have inside them. The formation and diversification of any new species is the outward manifestation of the actions of subvisible forms of life: the smallest microbes, bacteria, their larger descendants, the larger microbes, protists, and fungi, along with their intracellular legacies, organelles such as mitochondria and centrioles. Evolution emerges from the fact that these small living organisms and their progeny tend to outgrow their bounds."

They argue the main source of heritable variation for any given organism comes from the genomes of other organisms, which have historically come to be so related to others that a merging occurs. Natural selection determines if such mergers are successful.

The authors are explicit about their disagreement with mainstream evolutionary science. "No visible organism or group of organisms is descended 'from a single common ancestor,'" Margulis and Sagan write. The "common ancestor" concept is no doubt familiar to all who studied any evolutionary science at just about any level. Although "missing link" is usually frowned upon as a term about common ancestors, in effect, that's what common ancestors are viewed as—portions of the evolutionary tree whose identities are not yet fully understood and from which various extant species can trace their lineage. Margulis and Sagan replace the idea of an evolutionary tree that only branches outward with one that not only branches but also fuses as evolution occurs. If they are more correct than not, and they provide much evidence to support their theory, theirs is an exciting idea.

There's much more I want to discuss on this topic, but the discussion will have to continue in part II because this post has been sitting around for over a week and now I just want to get it up here.

*It should be noted that man's domestication of the wolf is pretty darn fascinating.

**As an aside, I think the inability of mainstream evolutionary scientists to point to current-day examples of speciation may be one reason that creationists, and their intelligent design brethren, remain able to sway converts despite the religiosity of their appeals. In the current educational paradigm, it's still too easy to view evolution as something that happened in the past, but which is too hard to observe today. Because science at its best is empirical, this was a public relations weakness for proponents of evolution by natural selection in general. As a member of the media, I can also appreciate the need for a contextual appositive—(i.e. "…speciation, for example as we see from organism X evolving from organism Y, is based on empirical evidence…).

***As another aside, punctuated equilibrium was very much taught in my classrooms, usually as opposed to gradualism. Why this concept never came to be linked in my mind to greater curiosity about the nature of speciation is somewhat curious, but probably attributable to the need to digest various textbooks in short order and to the lack of competing voices that complicate the discussion like those of Margulis and Sagan.