Multiple Realizability as a design heuristic in biological engineering

Abstract

Recently, several critics of the multiple realizability thesis (MRT) have argued that philosophers have tended to accept the thesis on too weak grounds. On the one hand, the analytic challenge has problematized how philosophers have treated the multiple realization relation itself, claiming that assessment of the sameness of function and the relevant difference of realizers has been uncritical. On the other hand, it is argued that the purported evidence of the thesis is often left empirically unverified. This paper provides a novel strategy to answer these worries by introducing a role for multiple realizability in the context of biological engineering. In the field of synthetic biology, bioengineers redesign the evolutionary realizations of biological functions, even constructing artificial chemical surrogates in the laboratory. I show how in the rational design approach to biological engineering, multiple realizability can function as a design heuristic in which the sameness of function and difference of realizers can be controlled. Although practically motivated, this engineering approach has also a theoretical, exploratory component that can be used to study the empirical limitations of multiple realizability. Successful realization of the engineering designs would amount to a concrete demonstration of multiple realizability, taking evidence for MRT beyond what is readily found in nature.

Could We Really Be Made of Swiss Cheese? Xenobiology as an Engineering Epistemology for Biological Realization

“…Xenobiologists and biological engineers often start from the opposing idea, namely, that biological functions can be realized in many different ways. [21] It is important to see that this is not the same thing as entertaining any kind of ontological commitment that this is always the case or that it follows from some kind of privileged first principles. Rather, it is best understood as a fruitful, yet fallible research heuristic, an intellectual stance to inquiry.…”

“…Rather, it is best understood as a fruitful, yet fallible research heuristic, an intellectual stance to inquiry. [10,21] Interestingly, the multiple realizability hypothesis of genetic functions has for some time been implicitly recognized in the scientific community as a potential source of application in biosafety engineering. [21,22] One particularly popular idea is to use different material media for genes to achieve orthogonal variants of a given engineered module.…”

“…[10,21] Interestingly, the multiple realizability hypothesis of genetic functions has for some time been implicitly recognized in the scientific community as a potential source of application in biosafety engineering. [21,22] One particularly popular idea is to use different material media for genes to achieve orthogonal variants of a given engineered module. For example, non-DNAbased genomes could act as genetic firewalls in synthetic organisms, preventing them from exchanging genetic information with naturally occurring species, while at the same time ensuring their other biological functionalities.…”

“…[22,23] The potential many-to-one relationship between different types of biopolymers and informational genes is thus not only a theoretical hypothesis, but also a practically motivated engineering goal. [21] Not any difference between realizers is enough to warrant claims of multiple realizability, however. After all, because of the prevalence of noise and natural variation in the living world, no two biological systems are exactly alike.…”

“…For example, a trait might have been originally selected for to perform a function F, but is currently favored because of its role in realizing another function G. Fortunately, in the case of xenobiology (and engineering more generally), some pragmatic criteria for the sameness of function can be obtained by observing the purpose behind the design. [21] Presumably, in order to count as functional XNA, a synthetic genetic system would need to be able to realize at least some important subset of the functional properties of natural DNA. To what extent this functional alignment can be achieved remains an empirical question.…”