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. 2015 Dec 6;5(6):20150040.
doi: 10.1098/rsfs.2015.0040.

Convergent evolution as natural experiment: the tape of life reconsidered

Affiliations

Affiliations

  • 1 Department of Philosophy , Boston University , Boston, MA 02215 , USA.
  • 2 Department of Biochemistry and Philosophy , Dalhousie University , Halifax, Nova Scotia , Canada B3H 4R2.

Convergent evolution as natural experiment: the tape of life reconsidered

Russell Powell et al. Interface Focus. .
. 2015 Dec 6;5(6):20150040.
doi: 10.1098/rsfs.2015.0040.

Affiliations

  • 1 Department of Philosophy , Boston University , Boston, MA 02215 , USA.
  • 2 Department of Biochemistry and Philosophy , Dalhousie University , Halifax, Nova Scotia , Canada B3H 4R2.

Abstract

Stephen Jay Gould argued that replaying the 'tape of life' would result in radically different evolutionary outcomes. Recently, biologists and philosophers of science have paid increasing attention to the theoretical importance of convergent evolution-the independent origination of similar biological forms and functions-which many interpret as evidence against Gould's thesis. In this paper, we examine the evidentiary relevance of convergent evolution for the radical contingency debate. We show that under the right conditions, episodes of convergent evolution can constitute valid natural experiments that support inferences regarding the deep counterfactual stability of macroevolutionary outcomes. However, we argue that proponents of convergence have problematically lumped causally heterogeneous phenomena into a single evidentiary basket, in effect treating all convergent events as if they are of equivalent theoretical import. As a result, the 'critique from convergent evolution' fails to engage with key claims of the radical contingency thesis. To remedy this, we develop ways to break down the heterogeneous set of convergent events based on the nature of the generalizations they support. Adopting this more nuanced approach to convergent evolution allows us to differentiate iterated evolutionary outcomes that are probably common among alternative evolutionary histories and subject to law-like generalizations, from those that do little to undermine and may even support, the Gouldian view of life.

Keywords: Stephen Jay Gould; contingency; convergence; exobiology; experiment; laws.

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Figures

Figure 1.

Figure 1.

( a ) A radically…

Figure 1.

( a ) A radically contingent system in which outcomes (morphological, functional or…

Figure 1.
(a) A radically contingent system in which outcomes (morphological, functional or relational) depend on improbable events occurring during the evolutionary path under consideration. For example, at t2, some paths are not taken (dashed lines) owing to non-replicable events, causing a number of evolutionary outcomes to become inaccessible at t3. Conversely, (b) a robustly convergent system in which many outcomes are still accessible from even very distant evolutionary trajectories. For example, very divergent lineages at t3 are still able to converge on the same evolutionary outcome at t4. (c) A mixed contingent/convergent system that exhibits path-independence and predictability at finer grains of resolution (reflecting evolutionary iteration within the developmental parameters of orders, classes and phyla), but exhibiting path-dependence and unpredictability when viewed at courser grains (e.g. across phyla or the whole of animal life). Such mixed systems are consistent with and arguably predicted by a Gouldian view of life that accords theoretical primacy to internal developmental constraints. This underscores the problem with interpreting all evolutionary repetitions, and even certain impressive convergences, as counterexamples to the RCT.
Figure 2.

Figure 2.

Here we illustrate three key…

Figure 2.

Here we illustrate three key dimensions of robustness with respect to which evolutionary…

Figure 2.
Here we illustrate three key dimensions of robustness with respect to which evolutionary regularities may be described. Each evolutionary iteration (labelled) is approximately located in a three-dimensional space along axes reflecting its degree of specificity, independence and scope, illustrating the extent to which it represents evidence against the RCT conceived either as a general thesis or as a particular thesis about specific evolutionary outcomes (with the strongest such cases found in the darkest shaded region). Some iterated regularities, such as hummingbird flowers or predator avoidance, do little to contradict the RCT, whereas others, such as image-forming eyes, constitute much stronger, though still not decisive, evidence against it. (Online version in colour.)

References

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