The animal sensorimotor organization: a challenge for the environmental complexity thesis

Another interesting issue derives from a comparison with sponges as discussed below. When it comes to the notion of an ASMO, sponges look like they already have most of the ingredients, while just adding ‘speed, integration and specificity’ would suffice to make this transition. An interesting question here is whether the sponge feeding strategy provided an impediment to making the step towards an ASMO. Macrophagy as a lifestyle could be the central factor behind the evolution of an ASMO. Even when feeding on non-moving food particles, ingesting them involve comparatively quick and precise manipulations, which requires a specialized body, which in turn requires a specialized developmental processes (Arnellos and Moreno 2016). In this case, one can envision a clear evolutionary route that leads from non-predatory macrophagy to a basic ASMO and a clear role for coordinative processes as a key feature behind this evolutionary process.

The notion of a specific animal sensorimotor organization or ASMO provides a central preadaptation for the subsequent evolution of complex active animal bodies that kick started the Cambrian Explosion of smart and fast animal life on this planet. Coordinating contraction-based effectors provided a way for macroscopic bodily and environmental features to systematically influence microscopic (intra)cellular processes, integrating them in a way that did not happen in other multicellular organizations. Once such an ASMO is present—such as in the case of cnidarians—and when there is space for the further developmental explorations of complex body forms—where the bilaterians must have had better cards—the Cambrian Explosion starts to look like a necessary consequence.

While the last remark is pushing too far, we do think that the ASMO notion is an important conceptual tool to think about the processes that gave rise to the first complex adaptive bodies, as well as about the ways in which brains, bodies and environments work together even now. We think that the ASMO concept adds an important organizational view to the current discussion on the origins of early nervous systems (see e.g. Arendt et al. 2015; Arendt et al. 2016; Jékely et al. 2015b; Moroz 2015), and also to current debates in cognitive science on embodied intelligence (see e.g. Chemero 2009; Barrett 2011; Turvey and Fonseca 2014).

In addition, the ASMO notion relates to the ECT, reflecting an internal coordination view, while the ECT stresses adaptation to environmental complexity. We have argued that epithelia—the fundamental building block of the animal organization—provide a congenial starting point for deriving the ASMO. The kind of evolutionary problems encountered in this reading relate to the internal coordination of development, behavior and physiology. The environment in this reading is cast as comparatively homogeneous (simple in ECT terms), not requiring complex cognitive features, except an integrated body that is capable of providing ways to digest large food particles lying around. The relevance of environmental complexity is comparatively small in this scenario.

For the ECT, there are various ways to resist this critique. Obviously, the account of the ASMO as presented here is preliminary and whether it will be accepted depends on further theoretical and empirical work. Any strong implication for the ECT will depend on how the ASMO notion fares. Another possibility we see is to stress macrophagy as a central environmental challenge that drives the evolutionary events discussed above. The problem here has been discussed and consists of the lack of environmental complexity involved in just eating larger food items. ECT might be defended here but this will require additional work to show how and why macrophagy entails environmental complexity.

Argyris Arnellos was supported by a KLI research fellowship of the Konrad Lorenz Institute for Evolution and Cognition Research in Klosterneuburg, Austria, when working on this paper.