Passage IV

NATURAL SCIENCE: This passage is adapted from David Quammen's book Natural Acts: A Sidelong View of Science and Nature (©1985 by David Quammen).

The concept of mind is not inappropriate as applied to the octopi, since these creatures have by far the most highly developed brain in their province of the animal kingdom. They belong to the phylum Mollusca, a large group of invertebrates mainly characterized by soft bodies, hard shells, and rather primitive patterns of anatomical organization, well suited to surviving inconspicuously on the sea bottom. Typical of the Mollusca are clams, oysters, snails; the octopi (and to a lesser extent their near relatives, the squids) are decidedly untypical. They are an evolutionary anomaly, a class of genius misfits who have advanced far beyond their origins.

The octopi have an elaborate fourteen-lobed brain, an organ so large that their brain-to-body-weight ratio exceeds that of most fish and reptiles. Mentally, they are more on a level with birds and mammals. They possess a capacity for learning, memory and considered behavior that makes them—with the exception of marine mammals—the most intelligent of all sea-dwelling animals. In a laboratory, they tend to be good at mazes, and perform well in tests of discrimination among visual symbols. This last talent depends partly upon their acute eyesight. Every octopus looks out at the world through a pair of extraordinary eyes—eyes about which, to a human, there is something unexpectedly and disquietingly familiar.

"The animal has eyes that stare back," according to Martin J. Wells, a British zoologist who is one of the world's experts in octopus physiology and behavior. "It responds to movement, cowering if anything large approaches it, or leaning forward in an alert and interested manner to examine small happenings in its visual field." Jacques Cousteau goes a bit further: "When a diver sees a giant octopus in the dim water, its great eyes fixed on him, he feels a strange sensation of respect, as though he were in the presence of a very wise and very old animal, whose tranquility it would be best not to disturb." One of Cousteau's assistants adds: "I have often had the impression that they are 'reflecting.'" Other divers and lab researchers make the same sort of comment, describing the same eerie sense of encounter, recognition, even mutuality. Lately I've had occasion to experience it myself, during three evenings of octopus-watching in a small university room filled with quietly gurgling tanks: the potent, expressive gaze of the octopus. These animals don't just gape at you glassily, like a walleye [a fish]. They make eye contact, as though they are someone you should know.

One of the reasons for the potency of that stare is simply a matter of proportion. Relative to the body sizeof a given octopus, the eyes are, like the brain, unusually large. (The ultimate record in this regard belongs to that octopus cousin, the giant squid—with an eyeball up to fifteen inches across, largest on Earth and twice the size of the eye of a blue whale.) Octopus eyes are also protrusive and mobile, bulging up periscopically when the creature's attention is caught, swiveling far enough fore and aft to cover all 360 degrees of horizon. But the real magic behind the octopod gaze is that those eyes bear a startling structural similarity to our own.

It's an exemplary instance of the phenomenon called convergent evolution. Two separate evolutionary paths are followed for millions of years by two disparate groups of creatures, arriving eventually at two separate but (coincidentally) very similar solutions to a common problem. In this case, the problem of translating incident light rays into coherent images conveyable to the brain. The vertebrate eye-the model we humans share with cougars and eagles and rattlesnakes, all having inherited the pattern commonly—is an ingenious contrivance combining a cornea, a crystalline lens, an adjustable iris, and a retina. That such an organ evolved even once, within the vertebrate line, represents a miraculous triumph of time and trial-and-error over improbability. The still larger miracle is that two very similar versions have appeared independently. The other belongs exclusively to the octopi and their close kin. Each of those squid and octopus eyes consists of a cornea, a crystalline lens, an adjustable iris, and a retina, functioning together in much the same way as ours.