Margarida Hermida (et al.), “Ontic causation in biophysics”
Channel: CEFISES at UCLouvain
Date: 2023-08-08

Talk given at the Mechanisms and Ontic Causation in the Life Sciences conference, the second workshop of the MeCauLife group.

(work with James Ladyman)

Abstract (abbreviated): Biological systems, such as organisms, cells, and subcellular components, involve physical, chemical and biological entities and processes at various scales. The causal effects produced by these entities are due to their specific properties and the interactions into which they enter, which also occur at different spatial and temporal scales. We take ontic causation to include physical causation broadly construed as involving physical, chemical, and/or biological entities. Ontic causation in biology occurs when there is such physical causation within biological entities that contributes to function. This paper argues that there is ontic causation at different scales in biological systems, but that also there is always mixing of scales, and no global levels. We also argue that the separation of the timescales of the dynamics of different kinds of processes within living systems is critical to biological function.

Biophysics studies the physical properties of biological systems and their environments, and how these interact with biological properties in the context of biological processes and activities (throughout this paper we take physical to mean physical, chemical, or both). Biological entities are not only composed of physical entities, but are also themselves physical objects subject to universal laws of physical science at various scales. Looking at causation from a biophysical perspective can therefore help us identify ontic causation in biological systems that spans multiple scales. Here we present some different scales of ontic causation in the context of a basic activity of a living biological system, namely, the flight of a bird.

First consider the scale of cellular respiration. Within the cells, respiration takes place in the mitochondria. The inner mitochondrial membrane causes the proton gradient that generates the proton-motive force, used to produce ATP. The proton gradient requires both the physical structure of the membrane (including its impermeability to protons), as well as the proton pumps, proteins integrated in the membrane that actively transport protons. Only the membrane as a whole can be identified as the entity responsible for causing the proton gradient, so the causal processes at this scale depend on the higher-scale entity function as an unchanging environment that determines the causal background.

These and other examples show that causation in a complex system such as a living organism involves the effective separation of the spatial, temporal, and energy scales of different entities and processes of ontic causation. For example, at the molecular scale, the electric potential of the proton gradient across the mitochondrial membrane is about 150-200 millivolts over a distance of about 5 nm. The proton motive force powers ATP production, which takes place at a rate of 10 million ATP molecules per second in each cell. Each ATP molecule releases about 8 x 10-20 J of energy when converted to ADP. By contrast, a small flying bird typically flaps its wings at an average frequency of around 10 Hz and has a kinetic energy of about 2 J.

The relevant different scales are not global in accordance with the idea that reality comes in levels (Wilson 2021), rather they are determined by the dynamics of the relevant systems. There is no global separation of physical, chemical, and biological scales, but there is local separation of scales, with different kinds of processes taking place at different scales involving both physical and biological entities. However, scales are always mixed to some extent just as the membrane provides the potential, so the local separation of scales is effective not absolute – hence there are no separate ontological levels (contra Wilson 2021). The functioning of the entire organism emerges from the dynamics of these different processes.