Grow smart and die fast: the peculiar evolution of the octopus mind

In the early months of 2016, a daring prison break happened in an aquarium in New Zealand. One morning, the aquarium manger Rob Yarell and his colleagues found a curiously empty octopus enclosure with the lid torn clean off. Had there been a case of octopus theft? Not quite. Inky the resident Maori octopus had opened the hatch, slipped out, and squeezed himself through a 50m long drainage pipe back into the sea. When questioned by the media about Inky’s motives for his great escape, Yarell replied: “he is just such a curious boy. He would want to know what’s happening outside”. And so, inky took matters into his own tentacles and did exactly that. This incredible story is one of many that reveal the ability of octopi to bewilder us. There seems to be no end to the absurdly novel behaviours that octopi can show, leaving us questioning: when did they get to be so clever? Octopi belong to the class Cephalopod which appeared in the early Cambrian ~522 million years ago, earning for itself a spot on the opposite end of Darwin’s tree of life from us brainy mammal vertebrates. In modern evolutionary thought, the most prevalent hypotheses suggest that intelligence evolved convergently alongside a slow life history and the presence of similar socioecological factors, however, scientists are still stumped by the question of whether intelligence in Cephalopods, with their incredibly short life span and rather different social behaviours can be explained by this model. The convergent route for the evolution of intelligence in many animals is largely supported by one main theory proposed by John Allman in 1993: the Cognitive Buffer Hypothesis (CBH). CBH explains that animals evolved large brains to create novel behaviours on the run, allowing them to adapt to completely new ecological niches. There are countless studies to support this idea: one showed that in 400 reintroduction events, animals with larger brains tended to become more situated in their new environment. However, because of the energetic requirements of brain development it takes longer for an animal to reach maturity. “There is also a significant correlation in primates between brain weight and female age at first reproduction”, writes Allman. This delay in reproductive age is what causes the evolution of a long life history. Examples include humans, (with the average lifespan of 73), orcas (which live to 30) and owls (which can even live up to 15). Octopi, on the other hand, despite having the largest invertebrate brain-to-body ratio, are lucky to reach 2. Another case where octopi stand out is the Social Intelligence Hypothesis, proposed by Humphrey in 1976, which credits the evolution of intelligence to the cognitive demands of living in large groups. Primates, Cetaceans and Corvids are incredibly social animals, displaying complex altruism, competition and the presence of long term bonds. Octopi? Well, not so much. They are, and always have been, quite solitary animals. Long term bonds between mates are quite rare - in fact, male octopi are known to abandon their mates if competing males are nearby. It is quite clear that octopi don’t fall into these expected patterns. So, could evolution have taken an alternate pathway to spark intelligence in our colourful, tentacled friends? In a groundbreaking journal article written in November 2018, Amodio suggested that it actually all came down to one event: when octopi lost their shells. During the Cambrian era, the ancient mollusk ancestors of octopi rose up from the seafloor by filling their shells with gas. Over time these shells were reduced and internalised, and finally in the Jurassic and Cretaceous periods, octopi completely lost them. As a result, octopi were subsequently able to occupy a wide range of new habitats. Most importantly, the loss of their protective shells made them more vulnerable to predation. These new pressures might have had a significant role in the emergence of complex nervous systems and, consequently, intelligence. However, Amodio reflects upon the need for further evidence to confirm this hypothesis. One way would be to find that octopi with larger brains are the ones living in more complex environments with more diverse predation - showing that these factors do play a key role in the development of intelligence.