Sudden impact: Darwin on cognition and a leap of faith

If scientists working in biology or a related field like psychology want to get attention, they will say something like this: Darwin was wrong, or made a mistake, or is insufficient to explain X, where X is whatever they are researching. It makes them seem to be proposing something important, because everybody agrees Darwin proposed something that changed our way of looking at life and ourselves. If we are saying he was wrong, a "paradigm shift" cannot be far behind...

Blogging on Peer-Reviewed ResearchSo a paper entitled "Darwin's mistake: Explaining the discontinuity between human and nonhuman minds" is a surefire attention getter. The moreso because it is in the prestigious Behavioral and Brain Sciences journal as a "target article" (which has a number of responses to it, followed by the authors' responses).

The authors are Derek C. Penn, Keith J. Holyoak and Daniel J. Povinelli (Penn et al.). Here is the paper's abstract:

Over the last quarter century, the dominant tendency in comparative cognitive psychology has been to emphasize the similarities between human and nonhuman minds and to downplay the differences as “one of degree and not of kind” (Darwin 1871). In the present target article, we argue that Darwin was mistaken: the profound biological continuity between human and nonhuman animals masks an equally profound discontinuity between human and nonhuman minds. To wit, there is a significant discontinuity in the degree to which human and nonhuman animals are able to approximate the higher-order, systematic, relational capabilities of a physical symbol system (PSS) (Newell 1980). We show that this symbolic-relational discontinuity pervades nearly every domain of cognition and runs much deeper than even the spectacular scaffolding provided by language or culture alone can explain. We propose a representational-level specification as to where human and nonhuman animals' abilities to approximate a PSS are similar and where they differ. We conclude by suggesting that recent symbolic-connectionist models of cognition shed new light on the mechanisms that underlie the gap between human and nonhuman minds.

So it looks like they are saying that human minds are a saltation in evolution, something not merely the addition of more neurons and interconnections, but truly a sui generis kind, something that might make humans special. And that kind is "physical symbol system" (PSS), which only we among all species have. It sort of sounds like there's some real trouble for an evolutionary account of mind, doesn't it?

Only there's not, not really. The authors bury the following in a footnote:

Let us be clear: All similarities and differences in biology are ultimately a matter of degree. Any apparent discontinuities between living species belie the underlying continuity of the evolutionary process and largely result from the fact that many, and often all, of the intermediate steps are no longer extant. In the present article, our claim that there is a “discontinuity” between human and nonhuman cognition is based on our claim that there is a significant gap between the functional capabilities of the human mind and those of all other extant species on the planet. Our point, to cut to the chase, is that the functional discontinuity between human and nonhuman minds is at least as great as the much more widely acknowledged discontinuity between human and nonhuman forms of communication. But we do not doubt that both evolved through standard evolutionary mechanisms.

So this is all about the size of the gap between humans and other animals, not about the origin of that gap. Not that this will deter those inclined to quote mine for anything that might make evolution seem false, but we can leave that steaming pile of detritus to one side for now.

The issue is twofold: 1. Is the gap between human and other animal minds merely quantitative, and is there something we have that they don't (i.e., a PSS)?, and 2. What is it that we have they don't? What is a PSS such that chimps, parrots and dolphins lack it? It helps to see the rhetoric involved: Darwin said that everything we can do came from a less elaborate predecessor, and we can see some versions of that predecessor in apes and other animals. Our authors say that is the mistake he made.

They adduce lots of interesting evidence to the effect that animals can or cannot do some things thought to be uniquely human: nonperceptual sameness judgements, analogical reasoning, rule following, higher order spatial relations, transitive inference, hierarchical relations, causal relations, and theory of mind are all listed and discussed to show that humans do cognitive tasks that animals cannot. This, of course, was never at issue, really, although we have considerable debate on what counts as some or all of these among animals. Irene Pepperberg, for example, in her response, recounts the ways in which some animals, including her beloved Alex, the African Grey, could do exactly what Penn et al say animals cannot do. Likewise, dolphin researchers Herman et al. reject Penn et al.'s claims regarding the capacities of those animals. It seems that "human-like" depends very much on what counts as the reference class, and the more one interacts with the animals in research, the more human-like they seem.

Some relative terms do not admit of degree. "Unique" is one of them. Something simply is, or is not, unique. Humans are not "especially" unique or "uniquer" than other species, and if we share features, however weakly, with other species, then in that respect the difference is merely quantitative. So we can for the moment ignore most of what Penn et al. offer up as evidence and go straight to their main claim: humans, and only humans, have a language that involves symbols, and only we are PSSs. If this is wrong, then so too is their overall position.

First of all, as their commentators Markman and Stilwell note, it may just be that most of the time human cognition is very much like the animals and not at all discontinuous. The appearance of discontinuity may be due to external ways of characterising human behaviour. In short, our language is the reason, but the use of it to describe the activities going on in symbolic ways, not the fact we can do that as such. The similarities are being overlooked. Second, it is clearly true that humans use symbolic reasoning more often and more generally than any other organisms, but it isn't necessarily the case that we alone do it at all. The ape language research indicates that once there exists a symbolic community, animals can use symbolic reasoning. So the evolution of human symbolic society, incrementally over time, may be the reason why humans seem so different, not some discontinuity of evolution.

What is the PSS hypothesis? It is based on an attempt to find a way to generate intentionality, that is, for symbols to be "about" something the symbols are not connected to or resembling. The notion is that intentionality arises in virtue of our (and any suitable system) being a formal system capable of processing symbols in sufficiently complex a way that meaning arises out of that process. In short, syntax determines semantics, a view that has been widely criticised.

It is also no coincidence that a major proponent of this computational theory of mind associated with the PSS is Jerry Fodor, who also is well known for his attacks on "Darwinian" accounts of mind. Unlike Penn et al. Fodor doesn't reject the idea that mind evolved gradually, but that it evolved by natural selection. Penn et al. argue that it didn't evolve by degrees but leave open the possibility that it was adaptive. But for something to evolve as an adaptation, it needs to have prior traits to act upon, so maybe that too is problematic here. It strikes me that something is amiss. If cognition is sui generis in humans, then how did it evolve? By a sudden leap? That view has been tried before, and failed.

There is a lot more to this paper and the responses than I can discuss without some time spent in analysis and further research, and I have this lecture to prepare, so I will content myself with this: the reason why humans seem to be so different and distinct could very well be that we suffer from an enormous case of confirmation bias. We see only what confirms that distinctness and ignore or downplay what disconfirms it. Very likely this is a case of what Dennett colourfully called the "white picket fence" around humanity that is so often built. We need to feel special. But given the failure of the sorts of accounts given for PSS and the suddenness of human evolution, such as Diamond's fanciful "great leap forward", I think we might need to believe that the mistake isn't Darwin's.

Update: I forgot to give a Hat tip to Mixing Memory. Also, Shared Symbolic Storage and George Junior have covered this paper as well.


More like this

Got your attention, right? That's the title of a paper by Penn, Holyoak, and Povinelli in April's Behavioral and Brain Sciences. Well, the full title is "Darwin's mistake: Explaining the discontinuity between human and nonhuman minds." Here's the abstract: Over the last quarter century, the…
One of the most interesting aspects of human behavior is our nearly infinite capacity to arrange and coordinate symbols. Think of the symbols that permeate our existence. Paper money has no value in and of itself. A wedding ring is just a band of metal. The progress of the science might even be…
Throughout the brief history of cognitive science, debates over the nature of knowledge representation have raged. In the 1970s, the debate was between those who thought that knowledge was represented as images -- modal, or sensory representations -- and those who thought that knowledge was…
Earlier this month I wrote two posts about the evolution of the eye, a classic example of complexity in nature. (Parts one and two.) I'd like to write now about another case study in complexity that has fascinated me for some time now, and one that has sparked a fascinating debate that has been…

It seems to me (and others) that quantitative changes in cognitive capacity can result in qualitative changes in behavior. A recent paper that talks about some of these same issues is Halford et al. (2007) Separating cognitive capacity from knowledge. TiCS 11, 236. You might find it interesting.

I'm interested to read that BBS paper. At the rate that I'm falling behind, I'll get to it in 10 or 15 years... :)

Even if I give them everything they claim, I don't see how this challenges anything about "Darwinism". Darwin proposed that all morphological characteristics are the result of small successive "genetic" (modern term, obviously, not Darwin's) changes. A "new" set of features certainly can result from a set of small genetic changes. If humans really do have some "unique" mental ability that just means that some of the key changes occurred after our split from our most recent common ancestor with chimps/gorillas. To put it another way (and tie in your previous post) kill off but one bat species, that would not mean that somehow bat flight does not have an evolutionary origin.

By Matt Silb (not verified) on 20 May 2008 #permalink

A couple of point:
1) Where does this Darwin fetish comes from? Raw darwinism was abandoned a century ago, and replaced by Neo-Darwinism which conserves selection, but with a different mechanism. Really, who cares what Darwin thought about cognition - it wasn't his field and there was no where close to the necessary data at the time -- it was just his speculation!

2) Gah -- Fodor and Putnam. Not scientist but BS'ers who go from introspection. What worthless material -- we should have defunded most of the philosophers a century ago; the should stick to philosophy of science and stop muttering about empirical/theoretical questions. They can't adequately distinguish between conscious symbolic manipulation and other kinds, since they're going from introspection, they're data sets can be enumerated simply: 1!

3) The question is whether we have some variation on Chomsky's "organ of language", which would have wide-ranging ramification through-out human thought processes. It's a squishy thing, unlike the abstraction of a PSS. It could be non-continuous, since you can have non-continuous evolution - for example, either your mouth or your ass is at the front end of the GI tube and it has been reversed in a single step in the evolution of deuterostomes. A single change could have created the primitive organ of language, however much it is distributed, and it probably isn't just for symbolic transforms -- that's just the most important use today.

It is fairly clear that the average person (and the average scientist via their assumptions) overestimates the human animal gap - because the similarities are generally either hard to pick (same tool used in very different ways) or accepted truth already (in addition to less valid psychological reasons).

When Darwin percieved that gap he would probably have actually seen it as even greater than how we see it as now.

I suppose you cant separate article publication from marketing so throwing around names like Darwin without much justification will always happen.