Abstracts

7th Annual Conference in Philosophy & Biology

Todd Grantham (College of Charleston, Philosophy)
“From Bands to Empires: Explaining the emergence of social complexity”

Maynard Smith and Szathmary depict the evolution of human society schematically as: “Primate societies —> human societies (language).” This formulation emphasizes two crucial steps in the evolution of human societies: (1) the evolution of altruism and cooperation in our primate ancestors, and (2) the evolution of language in Homo. While this schema correctly emphasizes the role of language, it ignores important subsequent processes. I argue (following Jared Diamond) that there is a pervasive trend from “band-level” social organization toward larger social groups. This trend is probably driven (rather than passive diffusion). Understanding this trend requires explaining the origins of the social institutions that promote cohesion in much larger social groups (e.g., division of labor, social mechanisms for conflict resolution, and the centralization of political power). I suggest that Boyd and Richerson-style cultural group selection – involving cultural processes that reduce variation within groups as well as competition among groups – provides one plausible way to explain much of this trend.

Samir Okasha(University of Bristol, Philosophy)
“Evolutionary Transitions in Individuality and Levels of Selection”

An evolutionary transition in individuality occurs when a number of free-living biological units, originally capable of surviving and reproducing alone, sacrifice their individuality and coalesce into a larger unit, generating a new level of hierarchical complexity. This process has happened repeatedly in the history of life, giving rise to the modern biological hierarchy. I consider some conceptual and foundational problems that arise in trying to theorise about evolutionary transitions in individuality. I argue that multi-level selection theory provides the natural framework for trying to explain evolutionary transitions in Darwinian terms. However, development of this suggestion leads to a problem, for standard multi-level selection models presume the existence of a hierarchy of reproducing units – which is the very thing that theorists of evolutionary transitions are interested in explaining, thus raising the threat of circularity. A number of possible solutions to the problem are explored.

Joan Strassmann(Rice University, Biology)
“Cooperation and conflict in social amoebae: the challenge of multicellularity through aggregation”

Nearly all organisms develop through a single-cell stage on their way to multicellularity, something that maintains within-organism genetic identity and cooperation. In contrast, the social amoebae (Dictyostelia) form a multicellular organism by aggregating. This aggregate crawls through the forest soil towards light and heat, and then forms a fruiting body in which about a fifth of the cells die, forming a sturdy stalk which the others climb. At the top they form hardy spores. How does chimerism impact within-organism conflicts of interest?  To what extent do group interests prevail over individual interests, as has happened in the major transitions of life? Dictyostelium discoideum is an ideal model for these questions because of its experimental tractability, its sequenced genome, its single-gene knockouts, and its short generation time. Though many actions of the multicellular individual are cooperative, the signature of internal conflict is large in this fascinating organism, and kin selection is a powerful framework for understanding these interactions.

Brett Calcott (Australian National University, Philosophy)
“Patterns of Explanation in the Major Transitions”

Here is one approach to the goals of this conference: pick a number of transitions (the origin of something multicellular, eusocial, or colonial) and show how some single explanation applies to all of them. For most of this paper, I plan to do the reverse. I’m going to pick a single transition (the popular volvox), and show how a number of different explanations have been applied to it. These explanations aren’t simply slight variations, but demonstrate quite different explanatory patterns. I suggest this has an important implication for work on major transitions: different explanatory patterns will pick out different kinds of regularities across transitions, and emphasize different enabling conditions for the origins of complex individuality.

Ellen Clarke (University of Bristol, Philosophy)
Three questions about individuation in modular and clonal organisms”

My paper asks three questions about individuation:

  • How are individuals delineated on ecological timescales.
  • How are individuals delineated from their offspring ontogenetically (what is the difference between reproduction and growth).
  • How are individuals created over evolutionary timescales from aggregations.

I ask the three questions of modular and clonal organisms. The ecological question asks what unit, ie the genet, ramet, or module, is the one to which fitness should be assigned. The ontogenetic question seeks to find a property or life cycle stage that marks out the beginning of a new life, and I explore Dawkins’ argument that when clonal plants send out runners this is not constitutive of genuine reproduction. Finally I will compare individuality in modular organisms to that in unitary organisms and examine their different evolutionary trajectories. My conclusions centre on the possibility of intra-organismal genetic heterogeneity and show that all three questions are mutually illuminating.

Andrew Hamilton (Arizona State University, School of Life Sciences)
“Rethinking the Origins of Sociality: Harvester Ants and the Dynamics of Group Cohesion”

For one hundred and fifty years the evolution of cooperation has been a standard problem in evolutionary theory. One central question has been how cooperative behaviors could have arisen and spread, given the assumption that they have fitness costs relative to selfish behaviors. Here we present data on dynamic social interactions between normally solitary harvester ants (Pogonomyrmex californicus) that argue for a reframing of this standard approach. In particular, these data suggest that cooperation is best understood as the product of dynamic interactions between individual organisms with particular genotypes. The question for this experimental system is not whether and how cooperation evolved by natural selection, but rather which proximate mechanisms drive the dynamics of the system. This approach is informed by noticing that cooperation is neither a trait nor a fixed attribute of organisms as some evolutionary models suggest, but rather a property of the group. Framing the issues in this manner leads to a discussion of which particular mechanisms are responsible for cohesion for the diad: what makes these organisms into a group? In this system, cooperation between ant foundresses is a product of dynamic interactions between individuals, with positive consequences for individual fitness.

Lauren McCall (Duke University, NESCent)
Are Human Cultural Institutions Group Level Adaptations?

There are two distinct types of behaviors: those that are directly due to evolutionary processes and those that are not.  Both are relevant to the evolution of human culture, and are easily confounded.  Variable behaviors like cultural traditions and institutions can mimic heritable, evolved behaviors by persisting or recurring under the influence of epigenetic and ecological stabilizing forces.  Further confounding is the fact that behavioral variability itself can be adaptive, giving rise to behavioral variants that are sensitive to the constraints of structured environments.  Non-evolutionary mechanisms underpinning behavioral adaptability run the gamut from physiological acclimation and environment-specific alternative behaviors (polyethisms), to the novel developmental resources introduced by the different types of learning.  Organismal adaptability limits the evolvability of behavior, especially in organisms with large, plastic brains and extended post-parturition development.  Hominid encephalization and life history make it impossible for cultural group selection to explain the range of cultural institutions that have appeared since the origin of Homo sapiens ~200kya.

Ioan Muntean (University of California San Diego, Philosophy)
“Dynamics and Emergence in the Definition of Living Systems”

John Collier and Cliff Hooker attempted to explain life and intelligence as “complexly organized systems”. Their analysis is two dimensional: the systems are classified according to complexity and organization and living systems are complex systems, self-organized in which redundancy is global and of higher order. The question I ask in this paper is whether the dynamical explanation, in particular the Collier&Hooker dynamical explanation is intrinsically linked to emergence. I want to explore the strength of this connection in this context as well as in the general discussion about emergence and dynamics. I conclude that the dynamical explanation, albeit powerful in itself, cannot grant emergentism.

Carl Simpson (Duke University, Biology)
“The evolution of reproduction during evolutionary transitions in individuality”

Evolutionary transitions in individuality may provide the clearest examples of multilevel selection in nature. Canonical cases are the aggregation of prokaryotic cells into eukaryotic cells, cells into multicellular organisms, and multicellular organisms into colonies or societies. In each case, the dominant level of selection, and the level which is most “individuated,” shifted from the members to the aggregate as a whole This shift in individuality is marked by the onset of reproduction at the level of the new whole, but how reproduction emerges at new levels is unknown. Here I show that the origin of a group-level reproduction breaks a trade-off between group-level heritability and within-group differentiation caused by the primitive fission mode of reproduction. Primitively, any member of an aggregation can potentially found a new group; any differentiation among members must be reversible if it is to be heritable and therefore constrains adaptive division of labour. This constraint is successfully broken by the origin of a reproductive division of labour where members specializing in reproduction of new groups are present along with differentiated members that lack the ability to reproduce new groups.

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