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The Animal-Human Dividing Line

Getting clear about the dividing line between animals and humans.

As I read through Michael Gazzaniga’s Human over the break, I was transported back to 1996 when I discovered—to my own satisfaction at least—what exactly the dividing line is between humans and other animals. In the book, Gazzaniga offers a nice review of the question of human uniqueness and points out the radically different notions that modern day academics have on the question. Some academics emphasize that any claims of human uniqueness stem from an anthropocentric view of the universe and an egocentric need to be seen as special. Certainly, there is a valid point here. One only need to look at Genesis and its idea that humans were given dominion over the earth and other animals to see that. But the notion that humans are biased and egocentric does nothing per se to negate the claim that humans are unique. Indeed, it is absurd on its face to claim that there is nothing about humans that is unique. When I address this question with my students, I note that, as remarkable as whales, elephants, and wolves are (see, e.g., here), they are quite far away from developing university courses that study their existence and wonder about their uniqueness!

In the Afterword, Gazzaniga tells how he asked his friends and family, as well as sent letters to leading scholars around the world, “In what ways do you think humans are unique?” He received many replies that said “I’ll get back to you”, but many never did. The answers he did receive had a nice cross section of the kinds of ideas that have been tossed around for a long time. Answers such as talking, bigger brains, fully opposable thumbs, tool usage and the like were present. He reported being a little annoyed that no one in his family said the “left-brain interpreter”, which is his answer to the question in a nutshell. (For information on Gazzaniga’s interpreter formulation, see the post script at the end of this blog).

In the body of the book, Gazzaniga does a nice job reviewing the major domains of academic exploration on this issue. This includes research into language, the implications of bigger brains and potentially crucial differences in neuroanatomy (e.g., mirror neurons) and genetics (e.g., FOXP2 gene), self-awareness and theory of mind, sociality, music, and technological evolution. All of these answers hit on clues, but none tie it all up into a neat little bow that crystallizes the answer. Gazzaniga’s interpreter function is the best single answer in the book, in my opinion. But it still isn’t the whole answer. It frames the neuropsychological mechanistic processes, but it does not really capture the form and function of human distinctiveness. And it fails to capture exactly how and why our self-consciousness system interprets the world the way that it does.

The answer that I stumbled across in the fall of 1996 can be summarized by the claim (with a clear play off of Descartes): We are because we justify.

The idea is that there was a tipping point in human language that emerged with the capacity to not only convey descriptive information, but to ask questions. Anyone who has raised a child knows that kids first learn simple commands and descriptions for objects (e.g., no, mommy, juice). After they get some command of descriptive language, a transformation happens, usually around the age of two. And that is they start asking questions.

Because there are many ways in which individual development replays evolutionary history, we can make the claim that there were periods of concrete descriptive language that then evolved into more abstract Q and A processes. It is the emergence of the Q & A that tipped human evolution into a completely different phase of being. Why? Well, one thing to notice is that we are engaged in a prototypical human activity that has a Q & A flavor to it. Given that these processes are so ubiquitous in human interaction and basically nonexistent in the rest of the animal kingdom gives us a good indicator that we are on the right path.

But why does questioning result in an evolutionary tipping point? Because, although questioning is relatively easy, answering questions raises a whole new series of problems. Go back and hang out with an intelligent, curious four year old: “Why don’t we eat cookies before we eat dinner?”; “Why are you bald?”; “Why is the sky blue?” As kids readily show, asking questions is much easier than answering them. That is why exasperated parents eventually say, “That is just the way it is!”

I realized that once language had tipped from descriptions and commands to a Q & A format, a very powerful adaptive problem had emerged, which I came to call the problem of justification. This point gets us close to Gazzaniga’s Interpreter. We need an interpreter because we live in a unique environment in the animal kingdom, one that involves Q & A communication.

But Gazzaniga does not hone in on the most important feature of the interpreter. The idea can be greatly strengthened by thinking about what kinds of interpretations the interpreter likely to generate. Here is a thought experiment that gets at this issue via an extreme example: Next time you are at a dinner party and you spill a glass of wine all over the host, say either: A) “Oh my, I am so sorry. That was a total accident; let me help clean it up!”; or B) “You know I have resented you for a long time, and my aggression built up to the point where I wanted to show you the hatred that has been in my heart.”

I am going to go out on a limb and use my deep understanding of human behavior to make the radical prediction that the responses your social group would have to your giving Reason B would be radically different from Reason A. This highlights a key point that extends the interpreter argument. The interpreter is not designed like a “court reporter” that simply generates the most accurate representation of events and offers up an answer. The interpreter is much more like a “press secretary” that develops a narrative that attempts to justify action in a way that takes into account the social matrix and the problem of social influence.

I have formalized the “We are because we justify” argument with three* interrelated ideas, which are: 1a) The Justification Hypothesis; 1b) Justification Systems Theory; and 2) The Tree of Knowledge System. Together, these ideas show: 1a) the design of the human self-consciousness system is fitted to solve the problem of justification; 1b) that language-based beliefs and values at the individual and social level are organized into systems of justification; and 2) the emergence of linguistic justification as a novel form of information processing launched human behavior into an entirely new dimension of complexity.

The human-animal problem is foundational to human knowledge systems in general and to the field of psychology in particular. There is a clearly identifiable dividing line. It is important that we get it right.


*In my earlier writing I did not separate out the Justification Hypothesis from Justification Systems Theory. I have found this a useful distinction more recently.

Gregg Henriques
Source: Gregg Henriques

**Post Script on Gazzaniga's Interpreter:

Some individuals experience severe seizures, which result from excessive, uninhibited neural firing that spreads throughout the brain. Beginning in the 1950s and 1960s, neurosurgeons began to cut the corpus callosum in the brains of some patients with severe seizures in an attempt to minimize the spreading of the out-of-control neural firing. The corpus callosum is the set of neural fibers that connects the two hemispheres of the brain, and thus when it is cut, communication between the two hemispheres is broken. These patients—who came to be called split-brains—generally lived normal lives but careful research revealed some striking findings. For example, some patients would report a condition called ‘alien hand syndrome’, in which the left hand (guided by the right hemisphere) would seemingly act as if it were controlled by a mind of its own. A patient with alien hand might go into the closet to get a blouse, and find that both her hands would reach for separate garments, and there might literally be a tragic-comic struggle between them!

Roger Sperry began to systematically research the consequences of split-brains. He devised a technique for sharing information with only one half of the brain, usually by presenting it to only the right or left visual field. These studies added findings to the idea that the brain is quite lateralized, meaning that the two halves of the brain specialize in different functions, with the left hemisphere being more linguistic and rational and the right being more spatial and visual. Michael Gazzaniga was Sperry’s student. He began to systematically study how split-brain patients would explain their actions. He reasoned that since it houses the language center, the left hemisphere would be the seat of self-explanation. He wondered what would happen if information was given only to the right hemisphere and people then acted on it. How would people explain their actions in the absence of the correct information? Gazzaniga (1992) found that if simple commands were flashed to the right hemisphere, such as "walk around" or "laugh," the patients would follow these commands (the right hemisphere does have rudimentary linguistic capacities). However, when asked to explain why they were performing these behaviors (e.g., walking or laughing), patients would confabulate a reason, and say "I am going to get a drink" or "Because you guys are so funny". In other words, their self-consciousness system justified the behavior in the absence of necessary information. Gazzaniga characterized the system of cognitive processes that allows for these interpretations to occur as “the Interpreter”. He wrote:

It is easy to imagine selection pressures promoting an interpreter mechanism in the human brain. A system that allows for thought about the implications of actions, generated by both others as well as the self, will grasp the social context and its meaning for personal survival….Also, the interpreter function generates the possibility for human uniqueness….I think that the built-in capacity of the interpreter gives each of us our local and personal color (Gazzaniga, 1992, p. 134).

For a YouTube demonstration, see here:

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