Cells, colonies, and clones: individuality in the volvocine algae

Biological Individuality

As I mentioned previously, I have a chapter in the newly published book Biological Individuality, Integrating Scientific, Philosophical, and Historical Perspectives. The chapter was actually written nearly five years ago, but things move more slowly in the philosophy world than that of biology. Finally, though, both the print and electronic versions are now available; here is the electronic version of my chapter. The book currently has no reviews on Amazon, so if you want to give it a read, yours could be the first. If you’re interested in current and historical views on individuality, there is a lot of good stuff in here, including contributions by Scott Lidgard & Lynn Nyhart, Beckett Sterner, Andrew Reynolds, Snait Gissis, Olivier Rieppel, Michael Osborne, Hannah Landecker, Ingo Brigandt, James Elwick, Scott Gilbert, and Alan Love & Ingo Brigandt.

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Look what came in the mail yesterday!

Biological Individuality

A project started five years ago has finally borne fruit. In May, 2012 I joined a group of philosophers, historians, and biologists in Philadelphia for the Cain ConferenceE pluribus unum: Bringing biological parts and wholes into historical and philosophical perspective.” The meeting was organized by Lynn Nyhart and Scott Lidgard, with the goal

…to pursue the question: How can historians, philosophers, and biologists help each other to understand part-whole relationships in biology, both today and in the past?

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J. S. Huxley part 2: Volvox

Last time, I wrote about Julian Huxley’s 1912 book, The Individual in the Animal Kingdom, and his use of the volvocine algae as an example. I liked most of what he had to say, though I took issue with his assertion that

…all the other members of the family except Volvox…are colonies and nothing more—their members have united together because of certain benefits resulting from mere aggregation, but are not in any way interdependent, so that the wholes are scarcely more than the sum of their parts.

This is, of course, a matter of how we define a multicellular organism, but I think any definition that excludes, for example, Eudorina, is not a very useful one.

This time, I’ll look at the rest of what Huxley had to say about the volvocine algae, most of which is about Volvox:

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J. S. Huxley part 1: Gonium

Julian Huxley was one of the biologists responsible for the merging of Mendelian genetics and Darwinian evolution in the early 20th century, the modern synthesis. His most influential work was Evolution: The Modern Synthesis, published in 1942. Thirty years earlier, though, he published a book on biological individuality, The Individual in the Animal Kingdom. Thankfully, the copyright on this book has expired, so it is now part of the public domain, and a scanned version is available for free in pdf and epub versions from Google.

Huxley Cover

Any book with Volvox on the cover can’t be all bad!

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What kind of individual do you mean?

One of the discussions I find most interesting in the philosophy of science is about what exactly constitutes a biological individual (or organism). The discussion would be a lot less interesting if everything were a vertebrate. Vertebrates (nearly always) develop from a single fertilized egg, so the (mostly) genetically homogeneous and (usually) genetically unique unit is the same as the spatially bounded, contiguous and physiologically integrated unit (this doesn’t even cover all the proposed criteria; see Clarke 2010 for a fairly comprehensive list with citations). But when we look outside of the vertebrates, what we often find is that some biological units have some of these properties and either groups or parts of those units have others.

Aphid on dandelion by Amoceann. Public domain image from Wikimedia Commons.

Aphid on dandelion by Amoceann. Public domain image from Wikimedia Commons.

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Multicellularity rundown

Too many papers, not enough time: each of these deserves a deep dive, but my list just keeps getting longer, so I’m going to have to settle for a quick survey instead. To give you an idea of what I’m up against, these papers were all published (or posted to bioRxiv) in July and August, 2016. By the time I could possibly write full-length posts about them all, there would probably be ten more!

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Problems with major transitions: Maureen O’Malley & Russell Powell respond

The Great Oxidation Event by Adelle Schemm.

The Great Oxidation Event by Adelle Schemm.

In a recent series of posts, I reviewed Maureen O’Malley and Russell Powell’s paper in Biology and Philosophy, “Major Problems in Evolutionary Transitions: How a Metabolic Perspective Can Enrich our Understanding of Macroevolution.” Although they made several good points, I thought that some of their criticisms were off the mark and that their proposed solution to the real and perceived problems with the major transitions framework was unsatisfying.

Drs. O’Malley and Powell are both heavy hitters in the philosophy of biology, and as I usually do when I dig deeply into someone else’s paper, I invited them to respond to my criticisms. They kindly provided a thoughtful rebuttal and permitted me to post it here. I’ll have more to say later, but for now I’ll just say that they make some good points and (most importantly) fairly represent my arguments. As usual for guest posts, I have made no edits to the content of their response, only formatted and added links:

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Time for a revision? Maureen O’Malley and Russell Powell on Major Transitions, part 3

Maureen O’Malley and Russell Powell say that the major transitions framework is in need of repair. They have a point, or rather several good points. I have looked at their criticisms of three different versions (the original framework as laid out in the book by John Maynard Smith and Eörs Szathmáry, Rick Michod’s ‘evolutionary transitions in individuality‘ framework, and Szathmáry’s revised ‘Major Transitions 2.0‘). But what is their proposed fix, and will it have the intended effect?

Figure 4 from O'Malley and Powell 2016. Two major aeons of evolution (modified from Falkowski 2006). ‘Gya’ stands for ‘billion years ago’; the date for the origin of photosynthesis may need to be pushed back (see Crowe et al. 2013).

Figure 4 from O’Malley and Powell 2016. Two major aeons of evolution (modified from Falkowski 2006). ‘Gya’ stands for ‘billion years ago’; the date for the origin of photosynthesis may need to be pushed back (see Crowe et al. 2013).

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Time for a revision? Maureen O’Malley and Russell Powell on Major Transitions, part 2

One of the cool things about studying the so-called major transitions is that they are as interesting to philosophers of science as to biologists. So you really can’t help being exposed to the philosophy of science literature, and many (maybe most) biologists in the field cross the lines at least occasionally. I’ve been to both, and I’m here to tell you that philosophy conferences are more fun than biology conferences.

Last time, I briefly summarized the various forms of the major transitions framework and addressed one of O’Malley and Powell‘s criticisms, that the framework is progressivist. Now I’d like to look at their other two problems: lack of unity and missing events. By and large, I agree with these points, although there are some caveats I’d like to point out. Next time, I’ll consider their proposed solution, which I’m afraid I don’t find helpful.

Disunity is actually O’Malley and Powell’s first criticism, but it will be a bit more complicated than progressivism to address, and I was short on time on part 1. Essentially, they are arguing that the major transitions are not a natural kind, philosophese for groupings that belong together because of some fundamental commonality, as opposed to more arbitrary groupings whose members are only superficially similar. So what are the transitions? Here’s the list from the book:

Table 1.2 from Maynard Smith J, Szathmáry E (1995) The Major Transitions in Evolution. Oxford University Press, Oxford.

Table 1.2 from Maynard Smith J, Szathmáry E (1995) The Major Transitions in Evolution. Oxford University Press, Oxford.

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Time for a revision? Maureen O’Malley and Russell Powell on Major Transitions, part 1

The so-called ‘Major Transitions’ framework is an attempt to explain the hierarchical structure of life on Earth: genes within chromosomes, chromosomes within cells, cells within cells (eukaryotic cells), individuals within sexual partnerships, cells within multicellular organisms, and organisms within societies. The best-known attempt to unify the origins of these relationships is a book by John Maynard Smith* and Eörs SzathmáryThe Major Transitions in Evolution.

MajorTransitionsCover

First published in 1995, the book focused on the origins of these hierarchical levels, connecting them with the unifying theme that

…entities that were capable of independent replication before the transition can replicate only as part of a larger whole after it.

For example, after a transition from unicellular to multicellular organisms (there were several), cellular reproduction either contributes to the growth of the organism or to production of new multicellular organisms.

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