Animal intelligence can be disconcerting and especially so when it is found in relatives of snails. Cephalopods are a class of molluscs that includes octopi, squid and pearly nautilus and they have remarkably advanced nervous systems. They display sophisticated communication, an ability to learn and remember on a par with mammals, and even a skill once thought to be unique to humans, tool use.
The antics of Paul the Octopus might have been diverting as he predicted the winners of the 2010 world cup but the real stories are in fact far stranger and more interesting. Chimps might look like us and it is easy to identify with dolphins but intelligence in octopi is almost alien. Creatures with eight tentacles and the ability to reason are not the product of science fiction, they are swimming in our oceans.
The octopus nervous system is different to that of vertebrates. Only a third of their neurons actually form their brain, the rest are distributed along the nerve cords of their arms. Their arms in fact show a high level of autonomy. Their reflex actions are so rather more complex than the ones vertebrates such as ourselves display.
Comparing intelligence between individuals of the same species is notoriously difficult. Comparing that of completely different organisms is practically impossible. However what we know of octopi has led to their intelligence being described by scientists as roughly equivalent to that of a dog or cat. They learn rapidly in laboratory experiments and it has been proved they have both short and long term memory.
The use of tools has been seen in vertebrates ranging from primates to birds. However octopi are the only invertebrates ever to have been seen practising what we would consider genuine use of tools, and this is taken to be a sign of sophisticated learning and problem solving abilities. The definition of tool use includes collecting an object to be ‘used on a particular occasion for a particular purpose’.
This is what veined octopi were shown to do with half coconut shells in a famous study, published in Current Biology in 2009. They picked up one or two halves and carried them around with them until they felt under threat. Then they would pull the half shells together to create a temporary shelter or pull it down over themselves if they only had one. Interestingly this must also be a new behaviour. There wouldn’t have been an abundance of half coconut shells on the sea bed until humans started eating so many and tossing out the shells.
Even more remarkable than this is the possibility that octopi might play, for the same reason mammals and birds do, to learn. Observations on captive octopi have shown them apparently playing with plastic objects by jetting water. Individuals behaved differently, with some spending far longer on this apparent play than others.
The problem with octopi developing their intelligence is a lack of social structure. Both male and female octopi usually die not long after mating. The females usually look after the eggs and then die shortly after they hatch. This means that the opportunity for one generation to pass skills onto the next is limited.
Octopi might be as intelligent as cats, but they cannot develop what would be the animal equivalent of ‘culture’. They do communicate with each other however, with some appearing to use their ability to change colour for this purpose.
The intelligence of octopi has been recognised legally in a number of countries. For example in the UK they are considered ‘honorary vertebrates’ and have similar rights to rats or mice in the laboratory. There is still a lot to be discovered about just what they are capable of and every new discovery is proving fascinating, if slightly eerie if you don't expect to find sentience in molluscs.