For much of the twentieth century, the dominant view in cognitive science held that complex thought and language were uniquely human capacities, and that the mental lives of other animals were, in comparison, impoverished and largely automatic. This view has been substantially revised by decades of research in comparative cognition. Chimpanzees have demonstrated the ability to use tools and to pass tool-use knowledge to younger members of their group in a way that looks remarkably like cultural transmission. Crows have been shown to manufacture multi-part tools — combining materials to create a composite hook to extract food from tubes — in ways that appear to require forward planning.
Octopuses present perhaps the most striking case. They belong to a completely different evolutionary lineage from vertebrates, and their nervous systems are structured entirely differently — with the majority of neurons distributed throughout their arms rather than concentrated in a central brain. And yet octopuses show sophisticated problem-solving, play behaviour, individual recognition of humans, and, in some experiments, what appears to be dreaming. Their intelligence evolved entirely independently of vertebrate intelligence, suggesting that complex cognition can emerge from radically different biological substrates.
The practical implication of this research is a matter of ongoing debate. If animals have richer mental lives than previously supposed, this has consequences for how we treat them in food production, research, and captivity. But the inference from ‘they have complex cognition’ to ‘they suffer morally in the way that demands comparable consideration’ involves philosophical steps that the empirical research alone does not settle.
