Gabora suggests that evolutionary mechanisms inside the brain can explain the origin of culture. This hypothesis is exciting and I agree with her in general. My commentary focuses on the nature of the parallel Gabora draws between natural and cultural evolution. I wonder whether the stream of thought is directly affected by selection processes. Instead, I suggest that behavior is selected. This shift of focus implies that the stream of thought is best considered as a process enhancing behavioral variation.
2. Gabora  suggests that drives, needs, attention focusing mechanisms and memory organization provide the necessary selection mechanisms inside the brain. However, she does not discuss the possible origins of these mechanisms, although the origin of culture relies as much on these selection processes as on the brain adaptations she describes. Obviously, the mechanisms she invokes were selected in natural evolution. These processes enhanced survival because they made organisms strive for the necessary goals at the right moments. Thus, one might say that these mechanisms select relevant behavior, once they have been activated. For example, foraging behavior will be selected instead of shelter seeking behavior when the organism is running out of energy. If behavior is already efficiently selected by these mechanisms, however, what could be the additional advantage of the stream of thought?
3. In natural evolution theory (e.g., Williams, 1992), an important distinction is made between the place where selection occurs (i.e. the phenotype) and the hereditary information (i.e. genotype). Selection processes are believed to affect the fitness of phenotypes. Only through these peripheral selection processes, do gene distributions change. The distinction between the physical information carriers and their environmental consequences is crucial. Applied to human behavior, the information carriers (which are called memes) are situated in the brain, whereas selection processes can only affect the external consequences of these information carriers. I accordingly prefer to consider behavior as the actual forum of selection (parallelling the phenotype), with some parameters in the brain (called memes) as the information carriers (parallelling the genotype). This small shift of focus in relation to Gabora's point of view has some interesting implications.
4. The first implication of this shift is that the role of the stream of thought changes from the unit of selection, as proposed by Gabora , to an intermediate step between the information carrier and its environmental effects. In selection theories, consequences reinforce the information carriers which enhanced a successful outcome. These information carriers hence have a greater likelihood of resulting in behavior in similar situations in the future. From this point of view, memes are not directly selected, their survival being affected only indirectly by their consequences. This indirect selection is similar to the selection of genes, which depends upon the success of the phenotype they result in. As a consequence, the stream of thought and Gabora's hypothesis about its origin can be considered an important variation-enhancing mechanism instead of the unit of selection. The organism endowed with the capacities Gabora outlines is reminded more often of previous similar situations. Such an organism accordingly perceives more similarities: it is capable of abstraction. This capacity allows it to generate more potentially beneficial behaviors.
5. A rapid change of thoughts is typical of the concept of "stream of thought." Without such a rapid change, there would be no stream at all. Reproduction, however, at least in natural selection, is characterized by stability (Williams, 1992). Stability follows from the "aim" of the selfish gene to reproduce itself (Dawkins, 1989). Gabora  states that the rapid change of thoughts is not harmful because it does not damage reproduction in general . I think the relevant question concerns not the potential harm done by rapid changes, but the stability of such a system. A new meme which enhances copying reliability is more likely to spread rapidly in the brain because it has a reproductive advantage relative to memes that do not enhance copying reliability. More specifically, if a meme which enhances copying reliability is activated, the likelihood that it is activated again increases. This process is apt to make different thoughts more similar to each other, up to a point where the same thought (say "I'm looking for my cave") is active all the time. Only another drive, which selects thoughts  could break down the "frozen" stream of thoughts and replace the first thought with another relatively fixed thought (say "I am looking for food"). The brain would rapidly return to a state typical of an episodic brain, as Gabora calls it , because the meme pool would rapidly shrink and fail to support a memetic brain. My point relies on Dawkins's (1989) concept of the selfish gene; I reject the idea that a meme exists to help the individual. Instead, behavior should be considered as the vehicle of memes. From this point of view, it is not plausible that the stream of thought is the place where selection occurs, because the stream is so volatile. This interpretation supports my claim that the relevant forum of selection is behavior, and that the process outlined by Gabora is in fact a variation enhancing mechanism.
6. Selectionist theories of the mind are promising because they replace miraculous explanations with more scientific ones. What I suggest in this commentary is to shift the main forum of selection from the stream of thoughts to behavior. As a result, the role of the new process Gabora proposes might be the acceleration of cultural evolution by means of increased behavioral variation.
The author was supported by a grant from the Fund of Scientific Research, Flanders.
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