What is the significance of science’s reliance on metaphor? Does the fact that much of the language of science is non-literal undermine its status as objective knowledge of reality or its ability to help us solve practical problems concerning the world and our health? What should readers keep in mind when they hear or read scientists employing metaphorical language?

Scientific language, especially that which is metaphorical, should be regarded as similar to provisional hypotheses that may require revision or ultimate rejection depending upon what the evidence suggests. We should also be aware that the metaphors scientists use may have quite positive effects for them in their original narrow application, allowing them to think about, understand, and possibly to manipulate some very specific and limited aspect of the world, but that the metaphor may be less adequate when applied to the broader system as a whole.

This chapter deals with the thorniest and most tangled thicket of metaphors, and there is probably no other area in the life sciences whose language has received so much critical attention. A great deal has been written about the metaphors used in genetics and genomics research, and I will attempt to provide only a summary here, with few original contributions of my own.

Classical genetics (that which preceded the “molecular revolution” of the mid-twentieth century) dealt with the phenomenon of biological inheritance, where evident species- and family-level similarities between parent and offspring attest that something is transmitted from one generation to the next (hence the metaphor of inheritance). Dogs give birth to dogs, corn plants produce more corn plants, and children tend to look like their parents and close relations.

While genes are said to provide the instructions, blueprints, programs, or recipes for protein synthesis, proteins themselves (which play structural and functional roles in the physiological activities of the cell), are commonly described as machines, motors, pumps, receptors, switches, messengers, recruiters, and cooperators that work together to carry out all the functions required of a living cell. Scientists employ these anthropomorphic and technomorphic metaphors to help themselves understand what proteins do and how they do it. As with the language of molecular genetics, there is often healthy debate among molecular biologists about the strengths and weaknesses of these metaphors for protein structure and function.

Medicine, as the old saying goes, is as much an art as a science. Its chief objective is the treatment and prevention of illness and disease. Biomedicine combines the traditional and practical objectives of medicine with modern scientific understanding of normal and pathological function in humans and other living organisms, but especially from the perspectives of molecular and cellular biology.

As earlier chapters explained, the experimental and molecular turn in biology of the twentieth century involved the adoption of an engineering perspective in two senses: (1) the goal is not simply to achieve an understanding of how living things function through passive observation, but rather to determine by intervention and manipulation of their component parts (cells and their own components) how they behave in different environments and conditions; and (2) this approach is guided by engineering metaphors that portray organisms and cells as machines that can be disassembled and rearranged in order to learn how the parts and whole function.

While other scientific-technological developments may have had greater material impacts on how we live (for instance, the unleashing of fossil fuels to drive the industrial revolution, atomic energy, or the creation of digital computers), none has had a greater impact on how we understand what it means to be human and our place in the universe than the Darwinian theory of evolution. Darwin was not the first to propose that humans and other species have not always existed in their present forms, and that they have gradually developed or emerged from earlier forms of life. Theories about the “transmutation” or “transformation” of species were proposed in Europe by members of his grandfather’s generation, including Lamarck, Geoffroy Saint-Hilaire, and Darwin’s own paternal grandfather Erasmus. In his own time, people like Robert Chambers and Herbert Spencer wrote popular and philosophical essays espousing what was frequently called the hypothesis or principle of development.

Given the wide range of possibilities to draw from, one might expect the metaphors being used in the life sciences to come from a wide variety of source domains. After all, if you’re trying to describe an organism and understand how it works, for instance, you could in theory compare it to anything. But as a matter of fact, the metaphors one tends to find in the life sciences fall into three broad categories: agents, machines, and information. I will refer to these broad categories as background metaphors. All three involve teleological thinking – that is, the assumption that things are (or that it is at least a helpful heuristic to suppose they are) either designed to fulfill certain functions or have plans of their own they are attempting to achieve. We will also look at a smaller number of metaphors drawing on natural objects as the source domain, but the majority to be covered in this book will fall into the three chief background metaphor categories of agents, machines, and information.

Darwin’s evolutionary view of life emphasized change over stasis. The older creationist account, meanwhile, supposed that species of plant and animal had been specially designed to fit perfectly the environments in which they live, and there was little reason therefore for them to change at all. Aside perhaps from the intermittent earthquake, volcanic eruption, massive flood, or other rare catastrophe, they were assumed to live in a stable environment. But Darwin had been convinced by Charles Lyell’s uniformitarian account of geology that the earth is in a constant state of change, and as a consequence species will have to adapt if they are to maintain a good fit to their surroundings. Over long periods of time, new islands rise up from the depths of the ocean due to volcanic activity, or sink as the ocean floor shifts; mountains rise and fall; periodic cooling and warming of the planet causes ice sheets and glaciers to expand and contract, leaving behind new lakes or deserts. So species evolve, migrate, or go extinct.

Metaphor has traditionally been considered antithetical to science. Metaphorical speech, which is commonly associated with the creative wordplay of poetry and fiction, would seem after all to be at cross-purpose to scientists’ efforts to articulate clear, rigorously precise, and objective statements of fact about reality. Aside from a tendency toward obscurity, the greater problem is that metaphorical expressions are typically false, literally speaking. Shakespeare’s Juliet is not literally the sun, time does not literally flow, and the genome is not a literal blueprint, book, or program. It is principally for this reason that scientists and philosophers of science have been, until rather recently, very critical of the suggestion that metaphor might play a legitimate role in the scientific process. In the early modern period, philosophers like Francis Bacon, Thomas Hobbes, and John Locke, who were enthusiastic advocates of the new scientific approach to understanding the world so brilliantly illustrated by the likes of Hooke, Boyle, and Newton, made withering criticism of metaphor as productive of nothing but falsehood and misdirection.

We have talked about genes and proteins and the various metaphors used to describe what they are, and how they function and interact with one another in the context of the cellular environment. Now it is time to look at the cell itself – the fundamental unit of life, the minimal system to which the property of being alive can be ascribed. While DNA and proteins are complex molecules with the capacity for chemical activity that is vital for life, neither of them can be said to be living. Nor can any other component found beneath the level of the cell as a whole: not amino acids (the components of protein), not polysaccharides (the large chains of sugars of which starch, cellulose, and chitin are composed), not water (which makes up more than 70 percent of the cell by content), not lipids (the fatty molecules that make up the membranes that surround the cell and many of its internal organelles), nor the organelles that carry out specific tasks within the cell.