Life: The Invention of Externalism

Jesper Hoffmeyer

In the Umwelt theory of Jakob von Uexkuell animals posses internal phenomenal worlds, Umwelts, which they project out into their surroundings as "experienced external" guiding marks for activity. Even bacteria may be said to posses Umwelts in the sense that tens of thousands of receptor protein molecules at their surfaces bind to selected molecules in their environment thus mediating measurements of the outside chemistry to patterns of activity at the inside. If the bacterium enters a nutrient gradient it will start moving upstream, and if it enters a gradient of bacterial waste products it will "know" to move downstream.

Seen from the human observer's point of view the Umwelt of an organism is a kind of world model, but seen from the organism's own "point of view" all there is situated activity, eventually accompanied by a sense of

awareness or even anticipation in the case of the most sophisticated animals. Thus, to describe living systems in terms of possessing Umwelts is still part of an externalist discourse even though it is an attempt to deal with the world as seen from the animal's point of view. This is because it is only in the historical perspective to which the animal has not itself access that the Umwelt can be described as a model.

The understanding that biology models the activity of model-building organisms is at the core of biosemiotics of course. Where bacteria are considered the subtleties of the situation stops here because the Umwelt of bacteria is mostly concerned with chemistry. But considering the Umwelts of more sophisticated organisms it becomes clear that these organisms have developed models of their surroundings which are very much aimed at the activity of other organisms and thus of other model-builders producing a semiotic web of infinite complexity. It remains an open question to which extent animals may understand that those other animals which they model in their Umwelts do themselves act on the basis of models. We can safely say, however, that the evolutionary road from the most primitive externalist models of the world as possessed by bacteria to the appearance of the first models capable of approaching an internalist perspective has taken billions of years to pass.

The fact that even prokaryotic organisms like bacteria have Umwelts must influence our understanding of the origin of life. It is suggested that it is the stable integration of self-reference and other-reference which establishes the minimum requirement for an Umwelt and thereby sets living systems apart from all their non-living predecessors. It is this double referential or semiotic character of living systems which is the true challenge to theories of the origin of life. And to my knowledge none of the present theories have tried to confront this most central aspect of life: the semiotic core of what it is like to be living.