DNA sequencing suggests why octopuses are so smart

By Graham Templeton
One of the weirder facts about the animal kingdom is that octopuses are actually quite smart. Octopuses exhibit all kinds of impressive behavior when tested. They can solve fairly complex spatial problems and remember patterns for later. They can learn and work toward a goal over time. They even engage in elaborate hunting behavior to trap or lure prey. The question is: why would octopuses be so much smarter than the animals around them, and how did they get that way?
A new study published in Nature has sequenced the octopus genome in order to discover just that. It looked at several different types of octopus tissue, analyzing the octopus’ surprisingly large genome. It contains many times more genetic information about making certain types of proteins, particularly those governing the growth and interaction of neurons. They have some 33,000 protein-coding genes to a human’s 25,000 — and those octopuses are smarter than they look. This still proves that when it comes to genome size, it really is all about how you make use of what you’ve been given.
Yet, unlike many large genomes, this one has not been duplicated. Some species of fruit fly have enormous genomes, but this is due to multiple duplications of their entire genome — they simply have more than they need. The octopus genome seems to have grown and elaborated the honest way, though genuine natural selection. This incredible evolutionary achievement has allowed a mollusk to become one of the apex predators of the sea.
The enormous and oddly diverse collection of genes makes the octopus genome a true oddity. University of Chicago researcher Clifton Ragsdale told Nature that “It’s the first sequenced genome from something like an alien,” referring to how unusual its proportions are. This study shows octopuses to have the second-largest gene family yet discovered, with 18,000 genes coding for versions of the zinc finger transcription factors — this is second only to elephants, with over 20,000 genes in the olfactory receptor family. Transcription factor adjust the expression of other genes, and the octopus seems to use these zinc finger genes in its most specialized tissues, like its suckers and camouflaging skin.
The squid is also surprisingly intelligent, for what it is, but still nowhere near as smart as the octopus.
One particularly interesting discovery is that octopuses seem to have biochemical systems in place that allow them to modify proteins on the fly, potentially changing their functions. Scientists speculate that this could allow the octopus to adapt its neural network to different tasks, allowing a plasticity that leads to the octopus’s incredible abilities in learning and memory. By some measures, its abilities can match those of a dog; the study features the example of an octopus opening a jar to get at the crab within.
The brain of an octopus is large, in terms of the number of neurons — the molluscs can have several times more neurons in their bodies than a mouse or rat. However, many of those neurons are distributed over the creature’s entire body, rather than being centralized in the cerebral cortex. A portion of the octopus-thinking hardware extend down the arms, allowing each one to do some basic thinking on its own. This may allow the octopus to use all its different limbs simultaneously, since they can each nominally detect and respond to their own surroundings.
Even a severed octopus limb can do basic “thinking” in the form of directed grasping. It’s sort of a super-charged version of our own spinal reflexes, which for instance allow us to unconsciously withdraw our hand from a hot surface before the brain has even registered any heat. The hardware for basic heat-response thinking exists in our upper spine, outside the brain, and the hardware for basic grip-finding and other tasks seems to exist in each of the octopus’ swirling limbs.
All this could help scientists learn not only how the octopus walked this remarkable evolutionary path, but perhaps more importantly, why.

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