From Peter Godfrey-Smith’s Other Minds, in a section describing the evolutionary tree:
Now let’s look for the common ancestor that connects this first group of animals, which includes ourselves, to an octopus. To find this animal we have to travel much further down the branches. When we find it, about 600 million years before the present, the animal is that flattened worm-like creature I sketched earlier.
This step back in time is nearly twice as long as the step we took to find the common ancestor of mammals and birds. The human-octopus ancestor lived at a time when no organisms had made it onto land and the largest animals around it might have been sponges and jellyfish (along with some oddities I’ll discuss in the next chapter).
Assume we’ve found this animal, and are now watching the departure, the branching, as it happened. In a murky ocean (on the sea floor, or up in the water column) we’re watching a lot of these worms live, die, and reproduce. For an unknown reason, some split off from the others, and through an accumulation of happenstance changes they start to live differently. In time, their descendants evolve different bodies. The two sides split again and again, and before long we are looking not at two collections of worms, but at two enormous branches of the evolutionary tree.
One path forward from that underwater split leads to our branch of the tree. It leads to vertebrates, among others, and within the vertebrates, to mammals and eventually humans. The other path leads to a great range of invertebrate species, including crabs and bees and their relatives, many kinds of worms, and also the mollusks, the group that includes clams, oysters, and snails. This branch does not contain all the animals commonly known as “invertebrates,” but it does include most of the familiar ones: spiders, centipedes, scallops, moths.
In this branch most of the animals are fairly small, with exceptions, and they also have small nervous systems. Some insects and spiders engage in very complex behavior, especially social behavior, but they still have small nervous systems. That’s how things go in this branch—except for the cephalopods. These are a subgroup within the mollusks, so they are related to clams and snails, but they evolved large nervous systems, and the ability to behave in ways very different from other invertebrates. They did this on an entirely separate evolutionary path from ours.
Cephalopods are an island of mental complexity in the sea of invertebrate animals. Because our most recent common ancestor was so simple and lies so far back, cephalopods are an independent experiment in the evolution of large brains and complex behavior. If we can make contact with cephalopods as sentient beings, it is not because of a shared history, not because of kinship, but because evolution built minds twice over. This is probably the closest we will come to meeting an intelligent alien.
How would we react to animals like the Octopus if they weren’t always in the background? What if they were newly discovered — or, indeed, if they had just landed on Earth from spaceships.
I think familiarity breeds indifference, and this is often to our detriment. For example, we’d be far astonished by what is happening with AI right now were it not already so ubiquitous — if, for example, there were only one computer terminal in the world capable of the astonishing feat of understanding natural language and creating paintings indistinguishable from those made by humans. If it weren’t already so typical, so suffused in the background of everything, wouldn’t we find it more astonishing?
And astonishment, I would argue, is the proper reaction — to aliens, to octopi, and to artificial intelligence.