Evolution in Four Dimensions (Jablonka & Lamb Reference Jablonka and Lamb2005) is a beautiful book, but I have a cavil. I am completely sold on the first three dimensions of evolution professed by Jablonka & Lamb (J&L): genetics, epigenetics, and behavior. I even grant that the proposed fourth dimension, the symbolic, has the three essential attributes of evolution: symbols are reproduced, their reproductions inherit some qualities from their ancestral line, and selection determines which reproductions will reproduce again. Nevertheless, honesty demands I explain why, as I see it, there cannot be a science of symbolic evolution.

We take it for granted that there are a finite number of biological species at any given time, and scarcely reflect how crucial this is for the theory of evolution. Imagine instead a continuous series of animals between humans and the chimps, between all hominids, between all mammalian species, and indeed between the different orders of extant organisms. In this continuum-world, Linnaeus would not have seen natural kinds like oaks, maples, pines, firs, and so on, but a confusing profusion of treelike organisms that graded off into other organisms along various dimensions; for example, into bushes and grasses along one dimension and into animals along another dimension, by way of carnivorous plants with digestive tracts and sensorimotor processes for the capture of animals. Even if evolution were occurring, it would be virtually impossible to tell.

The domain of the symbolic is like the continuum-world rather than the actual biological world. Symbols do not come in natural kinds but, instead, in shades of meaning that grade off along various dimensions. Note that when J&L speak of the symbolic dimension of evolution, the term “symbol” must be understood semantically rather than syntactically. What they are interested in, as they say many times, is the cultural transmission of information, because cultural information transfer causally interacts with biological evolution. Information is often transmitted symbolically, as in the sentence, “Snakes are dangerous,” which makes us cautious around snakes and so improves our fitness. However, this implies that the syntactically disparate sentence in French, “Les serpents sont dangereux,” is the same symbol as the English sentence, for it carries the same information. This example shows that symbols, in the sense J&L intend – and, in fact, require – for the fourth dimension of evolution, are individuated in terms of their semantics (not their syntax): in terms, that is, of their meaning. Sadly, there are no individual species of meaning, but only continuous shades of meaning. There exists no underlying code, no analogue of genes or DNA, and therefore no specific units of meaning that could undergo a process of evolution. In other words, there little hope for a genetics of semantics.

Need I point out that meanings are not physical, and that this poses a problem for physical sciences such as biology? Meanings are transmitted via physical events, certainly, such as the changing of a traffic light from green to red or the saying of words, but they cannot be discovered, even in the most minute scientific investigation of these events. Meaning is bestowed by cultural conventions, which are invisible (even though our physical movements are visible), implicit (upon what we do and say), and indeterminate (just as the cultural boundary between crime and misdemeanor is indeterminate). And even if the cultural conventions were scientifically determinate, what a symbol means is not always determined thereby. You may, for instance, know the rules of bridge, but the meaning of your partner's playing the king of clubs may still be a mystery. Is she flushing out lesser trumps? Or has she violated good strategy to inform you she is bored and would like to go home? We know that the spectrum of starlight may mean to an astrophysicist that the star is a red giant, even though the light left the star before human beings even existed, and before the cultural creation of astrophysics was even dreamt of. Therefore, the information contained is a function of the information the receiver is able to extract via his or her cultural information, whether we consider the playing of a king of clubs (a cultural event), or the light of a star (a merely physical event). Thus, there is no scientific measure of the information contained in a cultural act – the very concept may not be meaningful.

Worse yet, there is no sharp boundary between the literal and the metaphorical. The word “stick” comes from the Old English “sticca,” meaning twig. As it happens, twigs will get entangled in sheep's wool and in people's hair, and this primitive form of adhesion eventually led us to speak of tape “sticking” to a surface. Nowadays, we say tape literally sticks to things, but this meaning must have first been a metaphor: Some forgotten poetic genius first used the botanical noun to communicate the adhesive verb. Likewise, sticks of celery and candy were first metaphors inspired by their resemblance to twigs, whereas getting stuck by a pin was a metaphor inspired by pointed twigs' potential for puncture. This seems to be the universal pattern: literal usage is extended – but not literally – into a new domain by metaphor. The literal is just frozen metaphor, but is not literally frozen. Or is it? The “point” I am trying to make is that there is no sharp boundary between the literal and the metaphorical, as I said in the first sentence of this paragraph. You knew what that sentence meant, but did you stop to think that both “boundary” and “sharp” are metaphors? No. Nor is there any sense in doing so. Better that we realize that meaning is the bastard offspring of the literal and the metaphorical, so to speak, and reject the notion that cultural artifacts, words included, have literal meanings waiting to be discovered like phenotypes or genotypes. But this implies that there is no science of meaning, because science is the domain of the literal.

Finally, the human brain, which receives and replicates information, is utterly unlike the relatively monotonous biological mechanisms that copy DNA. The brain is a chaotic, unpredictable, disequilibrium device (Foss Reference Foss1992; Reference Foss2000) – the most complex thing in the known universe. Its workings have transformed the world itself in a quantum leap that created pizzas, movies, atomic bombs, lasers, and genetic engineering, all by means of meaning. Meaning is the mother of this explosion of invention, and J&L's metaphorical fourth dimension is this mother of invention. However, she is richer and wilder by orders of magnitude than anything else which science has encountered. She is, for now, one of the boundaries of, rather than one of the dimensions of, biological evolution. Her evolution, by contrast, remains a mere metaphor.