Biological Individuality: The Identity and Persistence of Living Entities

Biological Individuality: The Identity and Persistence of Living Entities

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For example, honey bee colonies appear to be Darwinian individuals even though they are not literally living agents.

1. The Focal Question: What are Biological Individuals?

Each individual bee within a colony is alive, but as suggested by the discussion of living agency in section 6 , it is only by invoking the cognitive metaphor that the whole colony itself can be said to be a living agent. Second, consider the outermost regions to the left and right of Figure 5 , regions 4 and 5.

Utility Contractor

There are both some parts and some groups of organisms that are neither organisms nor Darwinian individuals nor living agents. Most parts of the cellular machinery possessed by organisms, such as lysosomes region 4 or ribosomes, are biological individuals that, like genes, are not living agents, but unlike them, are not Darwinian individuals. Groups with this same status include higher taxa, such as species and clades discussed in section 4. Clades region 5 are neither organisms nor living agents. And even the most optimistic of clade selectionists will probably agree that a relatively inclusive and diverse taxon such Bryophyta , consisting of about 10, moss species, is not itself a Darwinian individual.

Bryophyta thus belongs in the far right of Figure 5. Third, consider the upper half of Figure 5 and regions 6 and 7. There are correspondingly two different types of living agents that are not Darwinian individuals: some parts of organisms such as hearts region 6 and again, perhaps more controversially , groups of organisms such as coral reefs region 7.

As physiological individuals, hearts are alive but they do not reproduce or relate to reproducers in the manner that Darwinian individuals do. As suggested at the end of section 6. Yet perhaps the reefs in addition to their constituent individuals have a better chance than eusocial insect colonies of counting as living agents.

Finally, what of the two remaining regions of Figure 5 , regions 8 and 9? These contain, respectively, biological individuals that are parts of organisms and are both Darwinian individuals and living agents, and organisms that are living agents but not Darwinian individuals. Some viruses are at least plausible candidate examples of the former category region 8 , since they have the internal complexity and unity of function possessed by physiological individuals but employ a scaffolded form of reproduction that relies on the replicative machinery of their host. And perhaps corporate organisms that are typified by tightly integrated multispecies complexes exemplify the latter region 9.

Consider again the Hawaiian bobtail squid plus its colony of Vibrio fischeri bacteria that Godfrey-Smith discusses as such an example see Figure 1 above. As such, it seems to be a living agent or physiological individual. But lacking a reproductive life cycle, it is not a Darwinian individual.

One might well argue, by contrast, that this feature of the squid- Vibrio complex also disqualifies it as an organism, making it no different in kind from coral reefs. Resolving this issue will turn partly on how exactly different sorts of reproduction are distinguished, and which sorts are required for evolution by natural selection, topics that have recently become more intensely debated e.

Figure 6 completes this running visual summary of conceptual space that biological individuals occupy, with the addition of a table which associates the regions with the examples discussed above. Figure 6: Biological Individuals in Conceptual Space.

This section explores their views of the regulation of evolutionary individuals. Queller and Strassmann note both that these things are matters of degree and that one can vary independently of the other.

Biological Individuality The Identity and Persistence of Living Entities

They use these parameters to define a two-dimensional space that represents a variety of biological individuals, as Figure 7 illustrates. To capture these ideas, it is useful to think of the feature that Queller and Strassmann believe is definitive of biological individuals as the internal ratio : it is the ratio of the level of cooperation between internal parts of individuals to that of the conflict between them.

The higher this ratio is, the higher the degree of individuality. Figure 7a indicates that, relative to other groups of cells, a mouse will have a relatively large internal ratio, while a yeast floc will have a relatively small internal ratio. Since the internal ratio considers only the level of internal control within a biological individual, focusing on it alone neglects the other aspect of autonomous agency that arose in section 6.

This external dimension to individuality can also be thought of as involving a ratio between cooperation and conflict—not between the parts of the individual but between that individual and other individuals that it interacts with. Just as an individual with a relatively large internal ratio has a higher level of individuality, according to Queller and Strassmann, so too would an individual with a low external ratio , i.

Biological Individuals

This refers to the ways in which new kinds of individual evolve slowly, over geological time scales, from recurring collaborations between different types of Darwinian individuals. Such partnerships sometimes lead to new examples of paradigm individuals, but other times falter or stall at the mere collaboration stage with no new individuals at all.

Utility Contractor

Closure of a pathway to a higher degree of individuality could be brought about by either a drop in the internal ratio reduced individuality because of internal matters or a rise in the external ratio reduced individuality because of external matters. In effect, Queller and Strassmann have proposed a view of evolutionary individuals that is exclusively focused on the regulation of the parts of an evolutionary individual as a means to avoiding subversion from within. In a series of papers, Ellen Clarke has developed a more integrative view of evolutionary individuals that develops this regulative dimension to biological individuality Clarke , , , a, b.

In work focused on plant individuality, Clarke emphasizes the mechanisms that constrain either sources of heritable variation, such as niche construction, bottlenecks, and polyploidy, or fitness differences, such as investment in root connections and the synchronization of flowering , Clarke then argues that something is an evolutionary individual if and only if it possesses what she calls policing and demarcating mechanisms There is a sense in which demarcating mechanisms operate in just the opposite way. For Clarke, it is what these two sorts of mechanisms do that is important, not how the mechanisms do this in various ways Clarke In other words, it is only the functions of the mechanisms that Clarke thinks are definitive, not the various material ways those functions are realized.

As Clarke stresses, this implies the multiple realizability of evolutionary individuals. For example, Dawkins, Maynard-Smith, and Bonner imply that certain material bottlenecks—narrowings between generations exemplified by our own single-celled, zygotic bottleneck—are essential ways for policing to be realized in evolutionary individuals Clarke — , while Ratcliffe and Kirk instead make material germ-soma separation essential Clarke The starting point here is the idea that the history of life is the history of the construction of more complicated biological individuals from simpler individuals, with natural selection operating at one or more levels facilitating the transitions between these individuals.

Underlying these ideas is the assumption that many or all biological individuals are hierarchically organized: earlier individuals provide the material basis for later individuals. For example, prokaryotes, which are single-celled organisms without a nucleus, form the material basis for single-celled eukaryotes, which do have a nucleus; in turn, single-celled eukaryotes serve as the material basis for multicellular eukaryotes. The evolution of biological individuals from prokaryotes to single-celled eukaryotes around 2 billion years ago, and from those to multicellular eukaryotes in the last — million years, are established facts.

In addition, there appear to be no counter-examples to this evolutionary trend.

Yet speculation and controversy surround almost everything else that has been said about these evolutionary transitions. Consider three such issues on which there is a sort of default position in the literature that remains subject to ongoing philosophical and empirical interrogation. First, it is common to view the evolution of individuality itself as the evolution of complexity.

There are, however, questions both about how complexity itself should be measured or conceived and about what empirical evidence there is for viewing the complexity of individuals as increasing over evolutionary time McShea Are the number of cell types that an individual has considered Bonner , the types of hierarchical organization it manifests Maynard Smith , or some more taxa-specific criterion, such as the information required to specify the diversity of limb-pair types Cisne ?

Fossils constitute a principal source for the criteria that have been proposed here. Yet different kinds of organisms leave fossils with distinct kinds of features, and some kinds of organisms are more likely to leave fossils than are others. One natural suggestion is that there may well be different kinds of hierarchies for the evolution of individuality, since kinds of individuals can differ from one another in more than one way. McShea provides an overarching framework in which eukaryotic cells can be viewed as evolving from differentiated aggregations of prokaryotic cells that have intermediate parts; multicellular eukaryotes as evolving from differentiated aggregations of single-celled eukaryotes; and colonial eukaryotes as evolving from differentiated aggregations of multicellular eukaryotes.

From Organizations of Processes to Organisms and Other Biological Individuals

These start with the transition from replicating molecules to compartmentalized populations of such molecules, and end with the transition from primate societies to human societies. Their discussion is focused primarily on exploring the processes governing each of the particular transitions they propose in terms of changes in replicative control. Second, it is common to view the trend from prokaryotes to multicellular eukaryotes as resulting from some type of directional bias, one that makes the trend a tendency supported by underlying mechanisms and constraints. But in supposing that there is some type of directional bias, each of these hypotheses might be thought committed to the sort of Panglossianism about adaptation that Gould and Lewontin are famous for critiquing, or more subtly to a view of evolutionary change as progressive or inevitable in some way.

Gould has used his discussion of the Burgess Shale Gould to challenge such views of evolution, arguing that the disparity of the fossils in that shale indicates that living things are significantly less different from one another than they once were. Gould argues that the range of biological individuals now on the planet is largely the result of highly contingent extinction events, and there should be wariness of immediately assuming that observed trends or patterns are adaptive or other tendencies. Third, many authors have recognized that whatever trends or tendencies there are in the evolution of individuals, there have also been changes over evolutionary time in the social relations between individuals e.

Yet how sociality should be integrated into a view of the evolution of biological individuals remains under-theorized for recent exceptions, see Birch and Okasha And however limited fossil evidence for individual structures and ecological niches may be, such evidence for the kinds and extent of sociality is significantly more sparse.

Much of the work to be done here seems distinctly philosophical in that it concerns how sociality is conceptualized. Should one accept the simple aggregation of individuals as a basic form of sociality? Perhaps the idea that sociality is not a relatively recent addition to multicellular life needs to be taken seriously. Instead, sociality may be a more sweeping feature of many if not all biological individuals, with the evolution of individuality understood in tandem with the idea of changing, shared, public and club goods.

This would make for a more dynamic and cyclical view of the history of life than has been assumed in past thinking about biological individuals. Conceptual Space, Distinctions, and Beyond Organisms 3.

Structuring Conceptual Space Beyond Pluralism 5. Locating Biological Individuals in Conceptual Space 8. Regulating Evolutionary Individuals 9. What makes something a biological individual? What is the nature of the category biological individual? Conceptual Space, Distinctions, and Beyond Organisms Responses to the Focal Question have advanced discussion of at least three closely related subsidiary questions: Beyond Organisms: In what ways does the traditional focus on organisms hinder us in thinking about biological individuals?

Distinctions: What are the most useful distinctions between various kinds of biological individuals? Conceptual Space: What is the most informative way to articulate the conceptual space surrounding the concept of biological individuals? Consider two positions that challenge the privileging of organisms in discussions of The Focal Question: Microbialism : Understanding the living world requires focusing on collaborations between macrobes and a variety of microbes e.

Eliminativism: Far from being paradigmatic biological individuals, organisms may be marginal or unusual special cases of biological individuals and should be eliminated from our ontology Haber , Okasha Andersson, Jan O.

2. Some Complexities: A Humungous Fungus and Coral Reefs

Wilson — Brown, James H. Calcott, Brett and Kim Sterelny eds. First edition Dennett, Daniel C. Ereshefsky, Marc ed. Reprinted in Ereshefsky — Gould, Stephen Jay and Richard C.

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