The Essential Tension

The Essential Tension

When I ran across The Essential Tension by Sonya Bahar, my first thought was that it sounded very much like something my PhD advisor could have written:

‘The Essential Tension’ explores how agents that naturally compete come to act together as a group. The author argues that the controversial concept of multilevel selection is essential to biological evolution, a proposition set to stimulate new debate.

The subtitle is Competition, Cooperation and Multilevel Selection in Evolution, which is more than vaguely reminiscent of the ‘cooperation and conflict’ framework Rick Michod has built over the last twenty years.

This won’t be a review, since I haven’t read the book. I’m not willing to spend $70 on the e-book, and the Google Books preview is missing too much to try to read it there. There are chapters on, among other things, multicellularity in Dictyostelium and Volvox, biofilms, and experimental evolution, though, so I’d be remiss if I didn’t mention it.

The Volvox chapter (“Multicellularity: Volvox“) seems, from what I can see on Google Books, to be a fairly straightforward review of Volvox biology and evolutionary relationships within the Volvocaceae. It gets fairly detailed in parts:

These laboratories [Richard Starr’s, Robert Huskey’s, and David Kirk’s] identified a panoply of mutants — MulB, MulC, MulD, MulX, MulA, MegA, R-1, R-2, RadA, doughnut, double-posterior, S16, pld, Inv, Dis, Exp, Rel, Flg, Eye, Rot, and many others…The Mul mutants are known as pattern-switching mutants, and cause asexual spheroids to develop in a pattern similar to male or female spheroids. MulB leads to asexual spheroids with gonidia distributed similarly to the eggs in a female spheroid…

The point of all this detail isn’t always clear, at least not from the parts I can see. There’s no indication of a larger theme until the very end (again, there could be larger themes in the pages not shown in the preview, but what I can see reads very much like a straightforward review of what we know about Volvox and its relatives). The end of the chapter goes straight from a discussion of extracellular matrix to a single paragraph of conclusions:

What does the remarkable life cycle of V. carteri tell us about the tension between competition and cooperation in the emergence of biological collectives? First the initial diversion of a lineage into various branches is not a particularly difficult task for evolution to accomplish. With the action of a very few genes, a temporal vegetative-then-reproductive lineage can be diverted into a spatially distributed lineage with coexisting vegetative and reproductive cells. This remarkable passage from time into space allows us to infer history from a series in true Darwinian fashion, and provides a window into the moments in evolutionary history when a group becomes and individual. The great complexity of the volvocine lineage, however, reminds us that this transition is no simple linear march toward greater complexity. In order to explore the transition to multicellularity with more precision, one would have to reproduce such evolutionary transitions in the laboratory. And that is precisely what researchers in the cutting-edge field of experimental evolution are doing.

This, of course, leads straight into the chapter “Experimental Evolution.”

The “proposition set to stimulate new debate,” in the publisher’s summary is that “multilevel selection is essential to biological evolution.” That IS certain to stimulate debate; I know this because it has been stimulating debate for half a century. In fact, most of the summary is about existing ideas, except for the ‘provocative new proposition’ at the end:

In Part I, the author explores the historical development of the idea of a collectivity in biological systems, from early speculations on the sociology of human crowd behavior, through the mid-twentieth century debates over the role of group selection in evolution, to the notion of the selfish gene.

Part II investigates the balance between competition and cooperation in a range of contemporary biological problems, from flocking and swarming to experimental evolution and the evolution of multicellularity.

Part III addresses experimental studies of cooperation and competition, as well as controversial ideas such as the evolution of evolvability and Stephen Jay Gould’s suggestion that “spandrels” at one level of selection serve as possible sources of variability for the next higher level. Finally, building on the foundation established in the preceding chapters, the author arrives at a provocative new proposition: as a result of the essential tension between competition and cooperation, multiple levels may be essential in order for evolutionary processes to occur at all.

That last could be original; it depends on what is meant by ‘multiple levels’. The Introduction may provide some insight:

One final tension will emerge from this discussion — a tension between levels of selection, between the individual and the group, and between the needs of the single organism and the species. I will investigate how this delicate balance is driven by the other tensions we have explored and how it relates to fundamental controversies in modern evolutionary theory, such as the role of group selection.

Okay, so clearly ‘multiple levels’ means multiple levels of selection (not, for example, vehicles and replicators). If the claim is really that evolution can only happen when multiple levels of selection exist (“multiple levels may be essential in order for evolutionary processes to occur at all”), that would be a bold claim. Going back to the Introduction, I’m not sure the claim being advanced is as strong as all that:

Finally, I will propose that the tension between the levels at which natural selection acts is not only essential but that, in fact, it is an inevitable result of the noisy interaction between biological objects at different scales.

I want to reiterate that I have not read The Essential Tension, so I can’t judge it. What I will say is that the publisher’s summary doesn’t convince me that the ideas it contains are particularly novel. It’s entirely possible that this is a failure of marketing rather than of scholarship. And even if the thesis of the book isn’t entirely new, it could be a useful synthesis of existing ideas.

The Essential Tension discusses many of the topics I write about here: evolution of multicellularity, multilevel selection, biological individuality, experimental evolution, and, of course, Volvox. If the price comes down or I can find a cheap used copy, I might post a review later.


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