I think examining the evolution of consciousness in animals helps shed light on it in humans. Admittedly, there are difficulties. Animals can’t self report using language, which limits just how much of their experience can be garnered from experiments. Still, taking data from human studies and combining it with animal studies can provide a lot of insight.
One issue is that, in the absence of a precise definition of “consciousness”, there is no sharp line in evolution where everyone agrees that consciousness begins. Scientists, such as Joseph LeDoux, who seems inclined toward animal consciousness minimalism, and Antonio Damasio, who’s more inclined to see it as widespread, can agree on all the relevant facts, but disagree on how to interpret them.
This leads many of us to come up with hierarchies. Those of you who’ve known me a while know mine:
- Reflexes and fixed action patterns
- Perceptions, representations of the environment, expanding the scope of what the reflexes are reacting to
- Volition, goal directed behavior, allowing or inhibiting reflexes based on simple valenced cause and effect predictions
- Deliberative imagination, sensory-action scenario simulations assessed on valenced reactions
- Introspection, recursive metacognition and symbolic thought
1 seems to apply to all living things, 2 to many animals, 3 to at least mammals and birds, and 4 to the more intelligent species, with 5, at least at present, only appearing to exist in humans.
But I’m far from the only one who’s come up with a hierarchy. I highlighted LeDoux’s a while back. Indeed, it appears to be an ancient tradition going back at least to Aristotle. The ancient Greeks didn’t have a word for “consciousness”, but they did write about the soul.
(The Greek word for “soul” is “psyche”, which obviously is where we get the term “psychology” from, but its etymology is interesting. It originally meant “to breath”, what probably seemed like the primary difference between living and non-living things.)
Plato’s conception of the soul was something immaterial that survived death, which resonates with the conception in many religions. Indeed, the word “soul” today is largely synonymous with the immortal soul of monotheistic theology. A lot of the way the word “consciousness” is thrown around today seems like an unwitting code word for this version of the soul.
Aristotle’s conception was more materialistic. Most people take him to regard the soul as part of the body and mortal. (Although, per Wikipedia, there is apparently some controversy about it.) And he had his own hierarchy back there in the 300s BC.
- The Nutritive Soul, enabling reproduction and growth
- The Sensitive Soul, enabling movement and sensation
- The Rational Soul, enabling reason and reflection
1 was labeled the “Vegetative” soul in the Wikipedia article on soul; it appears to apply to all living things. 2 applies to all animals. 3 is supposed to apply only to humans.
When I first read about this hierarchy years ago, it didn’t really work for me. My issue is that many animals appear to be able to reason to at least some degree. While debatable for fish, amphibians, or arthropods, all mammals and birds appear able to think through options and do short term planning. This seemed like yet another trait taken as unique to humans but where the real difference is a matter of degree rather than any qualitative break. Indeed, my thinking is that consciousness, if equated with baseline sentience, requires at least an incipient ability to reason.
However, I’m slowly making my way through Simona Ginsburg and Eva Jablonka’s The Evolution of the Sensitive Soul (which I was alerted to by Eric Schwitzgebel’s review). Obviously the title refers to Aristotle’s hierarchy, and the goal is to explain what the author’s call “minimal consciousness”, which they note is often referred to as “primary consciousness”, among other names.
And they equate minimal consciousness, sentience, with the sensitive soul. However, they don’t exclude all reasoning from the sensitive soul. (Indeed, their unlimited associative learning thesis, as I understand it, will require that it be there, but I haven’t reached that part of the book yet.) G&J draw the line at symbolic reasoning, involving language, mathematics, art, etc. That makes the rational soul equivalent to my own level 5 above.
I haven’t read Aristotle directly, so I don’t know if G&J’s characterization is closer than Wikipedia’s version. And I’m not sure “rational soul” is the most accurate way to describe it. And the sensitive soul itself has vastly varying capabilities across species. But minds, both animal and human, are complex things, and trying to boil down the difference to a single phrase is a lost cause anyway.
So, in this framework, all living things, including plants and simple animals, have a nutritive soul, many animals (but not all) have a sensitive soul, and humans a rational soul. G&J’s goals is to explain the sensitive soul.
What do you think of Aristotle’s hierarchy? Or G&J’s interpretation of it? I’m still inclined to use my own more detailed hierarchy (which admittedly still vastly oversimplifies things), but is Aristotle’s easier to follow?