Abstract
This paper proposes a new and testable view about the nature of species and other evolving lineages, according to which they are feedback systems. On this view, it is a mistake to think gene flow, niche sharing, and trait frequency similarities between populations are among variables that interact to cause some further downstream variable that distinguishes evolving lineages from each other, some sort of “species cohesion” for example. Instead, gene flow, niche sharing, similarities between populations, and other causal variables feed into each other—instances of these at earlier times help cause instances of these same variables at later times. And any lineage-identifying cohesion just is the recurrence or cycling of these feedback relations within metapopulations over generations. Such cohesion can then be represented as variable M within multi-dimensional variable spaces, where values of M vary dynamically with the frequency and magnitude of feedback relations. Related conditions for being a species or other evolving lineage are then clarified. To argue for the development and testing of this view, the paper shows how it improves upon others.
Highlights
The paper’s conclusion is that it would be worthwhile for some of the interdisciplinary community of researchers working on species and evolving lineages to collaboratively further develop and empirically test the feedback theory of evolving lineages elaborated here
One way to see that the more comprehensive view depicted in figure 2(c) fits better with the familiar idea that evolving lineages are dynamic, persisting things, is to consider how it removes the motivation for thinking—as we saw Mayr did and others do—that the relevant question for a species concept to answer is: what are the main causes of persisting trait similarities between conspecific populations? Because similarity is a variable just like all the others, and feedback relations feature between these, all those variables are effect variables in addition to causal variables
This paper’s conclusion is not, as noted in the introduction, that the feedback theory is true or probably true or well enough supported that we should adopt it. It is that it would be worthwhile for some of the interdisciplinary community of researchers working on species and evolving lineages to collaboratively further develop and empirically test the feedback theory of evolving lineages elaborated here
Summary
The feedback theory clarifies how trait frequency similarities may play surprising causal roles within feedback relations—how they may be causal variables just like gene flow and niche sharing and so on This motivates us to think more carefully about a widely perceived opposition between, on one hand, theories that base the nature of evolving lineages in causal relations, and, on the other, theories that base it in similarity (e.g., Hull 1976; Ereshefsky 2001). For instance Hull once lamented that some authors think trait similarities are more “fundamental” than interbreeding to evolving lineages of the species type, while he oppositely urged that interbreeding is more “fundamental” (1981, 145) Those sorts of fundamentality claims become dubious upon recognizing both interbreeding and trait similarities as just two among other important causal variables, between which it is the recurring feedback relations that constitute lineages.
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