Wolfram on complexity and evolution, with some observations on directionality

From my notes, 5.22.2002. Posted originally to Brainstorms.

Wolfram, S. (2002). A New Kind of Science. Champaign, Ill., Wolfram Media, Inc.

Let’s consider some of Wolfram’s remarks on biological evolution. He begins with the following (p. 383):

Biological systems are often cited as supreme examples of complexity in nature, and it is not uncommon for it to be assumed that their complexity must be somehow of a fundamentally higher order than other systems.

And typically it is thought that this must be a consequence of the rather unique processes of adaptation and natural selection that operate in biological systems. But despite all sorts of discussion over the years, no clear understanding has ever emerged of just why such processes should in the end actually lead to much complexity at all.

Wolfram, of course, is going to offer a different view, which I’ll get to in a moment. But first I want to comment on his characterization of biological thinking about evolution.

What I’m wondering is the extent to which those comments characterize what evolutionary biologists actually do in their technical work – whether it be explicating the fossil record, running experiments on peas or fruit flies, or doing computer simulations in population genetics, and so forth — as opposed to what gets said in meta-level statements about methodology and Big Issues. In his notes Wolfram indicates that he’s talked with many biologists and he asserts that “the further one goes from those involved with particular molecular or other details of biological systems the more one encounters a fundamental conviction that natural selection must be the ultimate origin of any important feature of biological systems” (p. 1002).

My (not very well informed) impression is that biologists are mostly indifferent to some notion of complexity (not necessarily to be identified with Wolfram’s notion), while a few are hostile to it, e.g. Stephen J. Gould, and a few are favorable, e.g. John T. Bonner. The discussions which come most immediately to my mind (because these are most relevant to my own work) are meta-level statements by evolutionary psychologists, which certainly do stress the adapted nature and complexity of psychological systems. But, beyond a general commitment to “the computational view of mind,” there is little discussion of the actual neural mechanisms underlying behavior, much less any attempts to characterize their complexity.

[On that score I note that, while human behavior seems vastly more complex than ape behavior, at least in an informal sense of the word, it seems hard to attribute that to a vast increase in complexity of the human brain over that of ape brains. The human brain is mostly larger, because it has many more neurons, but those neurons seem to be arranged in relatively simple ways. I’m inclined to agree with Ralph Holloway that there is some reorganization, but it’s not clear what that is. The human neocortex is certainly more richly folded, and I’m inclined to believe that has computational consequences; but that folding seems mostly the effect of the physical constraints of fitting a large cortical sheet into a specific volume. The differences between human and ape brains thus seem structurally simple.]

In any event, Wolfram is going to argue that complexity seems easy to come by and that we have no reason to believe that organisms are tightly adapted to their environments. The notion that complexity is easy to come by, of course, is one of the key ideas of this book: simple programs can produce complex behavior. In general, we cannot predict how programs will behave. Rather, we have to put them in operation and see what happens.

Wolfram makes a general argument that we see lots of regular patterns in organisms and that the underlying components (ultimately cells) of different organisms are drawn from a relatively small repertoire. I’m in no particular position to dispute this claim. He then goes on to wonder (386):

But just how are the programs for these and other features of organisms actually determined? Over the past century or so it has become almost universally believed that at some level these programs must end up being the ones that maximize the fitness of the organism, and the number of viable offspring it produces. . . . if one assumes that the program for each new offspring involves small random mutations then this means that over the course of many generations biological evolution will in effect carry out a random search for programs that maximize the fitness of an organism.

This is where he’s going to launch his attack. He refers to an earlier discussion of constraint satisfaction (which I have not read) where (p. 386)

for sufficiently simple constraints — particularly continuous ones — iterative random searches can converge fairly quickly to an optimal solution. But as soon as the constrains are more complicated this is no longer the case. And indeed even when the optimal solution is comparatively simple it can require an astronomically large number of steps to get even anywhere close to it.

He simply does not believe it makes sense to talk of evolution as involving a search for optimal solutions to adaptive problems. Most of the observed features of organisms simply (386) “represent solutions that were fairly easy to find, but are good enough not to cause fatal problems for the organism.” As far as Wolfram is concerned, relatively simple underlying processes make available a vast well of complexity from which organisms may draw, and thus “the vast majority of the complexity we see in biological systems has its origin in the purely abstract fact that among randomly chosen programs many give rise to complex behavior” (388). Correlatively “it is comparatively coarse features that tend to determine the success of an organism — not all the details of any complex behavior that may occur” (388).

Wolfram then goes on to discuss some implications of these ideas, including a few remarks on parallels between engineering design and “design” through natural selection (pp. 393 ff.). Toward the end of this section he addresses the directionality of evolution (p. 398):

Ever since the original development of the theory of evolution, there has been a widespread belief that the general trend seen in the fossil record towards the formation of progressively more complicated types of organisms must somehow be related to an overall increase in optimality.

This strikes a false note. Perhaps some biologist might say such a thing when pressed informally, but it doesn’t otherwise ring true. In any even, Wolfram continues:

Needless to say, we do not know what a truly optimal organism would be like. But if optimality is associated with having as many offspring as possible, then very simple organisms such as viruses and protozoa already seem to do very well. [Shades of S. J. Gould!]

So why then do higher organisms exist at all? My guess is that it has almost nothing to do with optimality, and that instead it is essentially just a consequence of strings of random mutations that happened to add more features without introducing fatal flaws.

While I do suspect that Wolfram is bouncing his view off a straw man biologist, I rather like what he is saying. But I want to follow Wolfram a bit more before adding an observation or two of my own.

Wolfram believes that natural selection’s “main contribution is to make things simpler, and that insofar as things do end up getting more complicated, this is almost always the result of essentially random sampling of underlying programs — without any systematic effect of natural selection” (398-399). He notes that while such random sampling is unlikely to have disastrous results in the case of “superficial aspects of organisms — such as pigmentation patterns” that things are different when “dealing with the basic structure of organism” (399). Here random changes are likely to have “immediate disastrous consequences. And in a sense it is natural selection that is responsible for the fact that such programs do not survive” (399). He goes on to say (399):

So does this then mean that there can never be any kind of general theory for all the features of higher organisms? Presumably the pattern of exactly which new features were added when in the history of biological evolution is no more amenable to general theory than the specific course of events in human history. But I strongly suspect that the vast majority of significant new features that appear in organisms are at least first associated with fairly short underlying programs.

I am sympathetic to this idea and note two things: 1) It directs our attention to the detailed properties and capabilities of genomes and phenotypes rather than the rather looser characteristics of environments. 2) I think the same considerations hold in the cultural domain. Rather than considering these notions, however, I want to make a comment about directionality.

And that comment is this: one reason more complex forms turn up over the long haul is that there is no where else to go but up. Let’s conduct a thought experiment. We’ve got ourselves a vast pool of pre-biotic soup just at the edge of life’s emergence. Thus every once in awhile full-fledged reproducible life emerges. At which time some malevolent external force (perhaps the evil twin of Maxwell’s Demon) destroys it, allowing the remains to disperse into the soup.

What happens over the long term? I would expect that life emerges time and again only to disappear. Always, this is life in its simplest forms, whatever they may be. We never ever, no matter how long we observe, see the spontaneous emergence of many-celled organisms much less see the emergence of creatures exhibiting intelligent behavior.

In fact, this is not what happened. There is no malevolent external force. So as life emerges, those living creatures remain in the soup and we see the accumulation and proliferation of living forms. Sooner or later some simple program will kick out a more complex form and some of those will survive, providing a substrate for yet more complex forms to emerge. As long as the sun provides free energy and the genes kick out new programs, this process can keep on going.