When the path is never shortest: a reality check on shortest path biocomputation

TL;DR

This paper critically examines the ability of two single-celled organisms, Physarum and Paramecium, to solve shortest path problems, highlighting experimental challenges and the organisms' limitations in reproducibly performing such computations.

Contribution

It provides experimental data and analysis showing the difficulties in using biological organisms for solving shortest path problems, emphasizing the need for standardization and better understanding.

Findings

Neither organism efficiently solved shortest path problems under tested conditions.

Biological variability and non-halting behaviors hinder reproducibility.

Experimental stimuli can adversely affect organism responses.

Abstract

Shortest path problems are a touchstone for evaluating the computing performance and functional range of novel computing substrates. Much has been published in recent years regarding the use of biocomputers to solve minimal path problems such as route optimisation and labyrinth navigation, but their outputs are typically difficult to reproduce and somewhat abstract in nature, suggesting that both experimental design and analysis in the field require standardising. This chapter details laboratory experimental data which probe the path finding process in two single-celled protistic model organisms, Physarum polycephalum and Paramecium caudatum, comprising a shortest path problem and labyrinth navigation, respectively. The results presented illustrate several of the key difficulties that are encountered in categorising biological behaviours in the language of computing, including biological variability, non-halting operations and adverse reactions to experimental stimuli. It is concluded that neither organism examined are able to efficiently or reproducibly solve shortest path problems in the specific experimental conditions that were tested. Data presented are contextualised with biological theory and design principles for maximising the usefulness of experimental biocomputer prototypes.