The increase [in complexity] has been neither universal nor inevitable. Bacteria, for example, are probably no more complex today than their ancestors 2000 million years ago. The most that we can say is that some lineages have become more complex in the course of time. Complexity is hard to define or to measure, but there is surely some sense in which elephants and oak trees are more complex than bacteria, and bacteria than the first replicating molecules.
By Ernst Haeckel – Kunstformen der Natur (1904), plate 17: Siphonophorae (see here, here and here), Public Domain, Link
Derek Skillings from University of Bordeaux/CNRS has a new article at Aeon about biological individuality:
For millennia, naturalists and philosophers have struggled to define the most fundamental units of living systems and to delimit the precise boundaries of the organisms that inhabit our planet. This difficulty is partly a product of the search for a singular theory that can be used to carve up all of the living world at its joints.
Skillings reviews the deep historical roots of the question, touching on the views of Charles Darwin and his grandfather, both Huxleys (T. H. and Julian), Herbert Spencer, and other 19th and early 20th century thinkers, as well as some more recent authors, including Daniel Janzen and Peter Godfrey Smith.
Jordi van Gestel and Corina Tarnita have published a ‘Perspective’ in PNAS, “On the origin of biological construction, with a focus on multicellularity“:
…we propose an integrative bottom-up approach for studying the dynamics underlying hierarchical evolutionary transitions, which builds on and synthesizes existing knowledge. This approach highlights the crucial role of the ecology and development of the solitary ancestor in the emergence and subsequent evolution of groups, and it stresses the paramount importance of the life cycle: only by evaluating groups in the context of their life cycle can we unravel the evolutionary trajectory of hierarchical transitions.
Figure 2 from van Gestel and Tarnita, 2017. Relationship between life stages in hypothesized life cycles of solitary ancestors and group formation in derived group life cycles. (Upper) Simplified depiction of hypothesized ancestral solitary life cycles of the green alga Volvox carteri, the cellular slime mold Dictyostelium discoideum, and the wasp Polistes metricus. Life cycles here consist of a life stage expressed under good conditions (black) and a life stage expressed under adverse conditions (green). For the latter life stage, we show an environmental signal that might trigger it and some phenotypic consequences. (Lower) Simplified depiction of group life cycles of: V. carteri, D. discoideum, and P. metricus. Developmental program underlying life stages in solitary ancestor is co-opted for group formation (shown in green): differentiation of somatic cells (V. carteri), fruiting body formation (D. discoideum), and appearance of foundress phenotype (P. metricus).
Dinah Davison and Erik Hanschen.
A couple of weeks ago, I indulged in a little shameless self-promotion, writing about my new chapter on volvocine individuality in Biological Individuality, Integrating Scientific, Philosophical, and Historical Perspectives. Now two graduate students in the Michod lab at the University of Arizona, Erik Hanschen and Dinah Davison, have published their own take on volvocine individuality in Philosophy, Theory, and Practice in Biology (“Evolution of individuality: a case study in the volvocine green algae“). The article is open-access, and Hanschen and Davison are listed as equal contributors.
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 Conference “E 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?
The 2017 Astrobiology Science Conference in Mesa, Arizona is just over a month away (April 24–28), and the abstracts are now available at the website. As a reminder, discounted registration ends March 27th.
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:
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.
Any book with Volvox on the cover can’t be all bad!
The website for the Volvox 2017 conference is up at www.volvox2017.org. Registration isn’t open yet, but there’s some information about the venue, the Donald Danforth Plant Science Center in St. Louis. The meeting is set for August 16-19, 2017.
The goal of the International Volvox Conference is to bring together international scientists working with Volvox and its relatives (aka Volvocales or volvocine algae). We cordially invite experimentalists and theorists interested in these fascinating organisms.
I’ll keep you posted!
Sex didn’t always involve males and females. I know it still isn’t always between males and females, but that’s not what I mean. I mean that there was a time when sex was happening, but there were no males and females. Sex existed before males and females, and many species are still doing it without them.