A foundational paper by philosopher Peter Carruthers, titled “Evolution of working memory“, delves into one of the most significant yet underexplored topics in cognitive science: the evolution of working memory. This crucial mental faculty, which acts as our brain’s active workspace, is fundamental to reasoning, planning, and intelligence.
Carruthers notes that while it has been “intensively studied for many decades,” there has been “very little comparative investigation of WM abilities across species”. By examining the minds of animals, we can begin to piece together the story of how our own powerful cognitive tools came to be.
Understanding Our Mental Workspace
Working memory (WM) is best understood as the mind’s conscious “scratchpad.” It is the system that “enables one to activate and sustain…a set of mental representations for further manipulation and processing”. This workspace is famously limited, with a general capacity restricted to “three or four chunks of information at any one time”.
Despite its small size, its power is immense. An individual’s WM ability is a strong predictor of performance in many other areas and accounts for a huge portion of what we call fluid general intelligence. This link between WM and high-level thinking is a central theme in the story of its development.
Animal Minds and the Evolution of Working Memory
A key question in the evolution of working memory is whether this ability is uniquely human. The most extreme position, that animals lack WM entirely, can be confidently dismissed. Numerous studies, such as those using match-to-sample tasks, show that animals can hold information in mind for several seconds, far beyond the 2-second window of simple sensory memory.
More surprisingly, evidence suggests that the raw capacity of animal WM may not be so different from our own. Experiments have shown that monkeys can track three to four items, and horses can distinguish between buckets containing two versus three apples. These findings suggest that the basic retention ability of three to four items is not exclusively human and could be a trait that is highly conserved across mammals.
The Real Difference: Not Capacity, but Control
If capacity isn’t the main difference, what is? Carruthers points to the executive control of attention, particularly the ability to resist interference. It turns out that simple memory span is not a reliable predictor of fluid intelligence in humans; rather, performance on “complex span tasks,” which require you to maintain information while doing something else, is.
This appears to hold true for animals as well. In a fascinating series of studies with mice, researchers found that a general intelligence factor was “strongly correlated with performance in a more complex WM task, in which the animals have to resist interference from competing memories”. Simple retention, however, showed no significant correlation. This suggests the crucial step in the evolution of working memory wasn’t just about holding information, but about protecting that information from distraction.
What Makes Human Working Memory Unique?
While the core WM system seems to be shared, humans possess unique tools that vastly expand its power. The most significant of these is language. Our ability to engage in “inner speech” provides a powerful method for rehearsing and refreshing information that animals simply don’t have.
Furthermore, our “vastly greater conceptual repertoire” allows for more effective “chunking,” a strategy where we group information to overcome the three-to-four-item limit. It may also be that humans are unique in their tendency for “mind wandering,” frequently using WM in ways “irrelevant to any current task” to imagine future scenarios and explore creative ideas.
The evolution of working memory is a story of shared foundations and unique human adaptations. While other animals possess homologous systems for holding information in mind, humans “excel in their abilities to withstand interference and to deploy attention” in flexible ways, amplified by the power of language. As Carruthers concludes, much remains speculative until more comparative research is done, but the available evidence paints a clear picture of how our extraordinary minds were built upon an ancient cognitive blueprint.