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Andy SmithAndrew P. Smith, who has a background in molecular biology, neuroscience and pharmacology, is author of e-books Worlds within Worlds and the novel Noosphere II, which are both available online. He has recently self-published "The Dimensions of Experience: A Natural History of Consciousness" (Xlibris, 2008).



A Response to Stewart

Andy Smith

Another way of putting this is to say that there is far, far more contingency in the process of evolution than there is in the process of biological development.

In Evolution's Arrow and other writings, John Stewart has argued that evolution is inevitably or inexorably progressive, driven by cooperation among living things. In my article Evolution's Quiver, I suggested that evolution is sometimes, but not always, progressive in this sense. I described it as a process that “leads to increasing complexity in some forms of life—which constitute the leading edge, so to speak—but not in all of them. In this view, increasing complexity is one way that organisms adapt to their environment, but not the only way.”

In his most recent article, A Wider Perspective on Evolution, Stewart responds to this:

Interestingly Smith acknowledges in his essay that evolution is headed towards the emergence of such an integrated global entity. But he does not appear to also see that this confirms the existence of an overall direction to evolution – towards the progressive integration of living processes into cooperative organizations of increasing scale. Apparently his failure to appreciate this is due to an assumption he seems to make about directionality. He appears to assume that if there is an overall direction to evolution, it must be towards the increasing complexity of organisms themselves.

I emphasized in "Evolution's Quiver" that I mostly agreed with Stewart's view of evolution, and I think our apparent difference here is to a large extent semantic—i.e., what it means to say that evolution has an overall direction (a term, by the way, that I never used in "Evolution's Quiver"). I certainly agree with Stewart that one evolutionary direction—again, what I call the leading edge—is now creating or could create a planetary form of life that transcends any single species of organism, including our own. My point was that if this is the overall or only real direction of evolution, then all species should evolve into this higher form of life, not simply our own. If they don't, then we are simply speaking of a leading edge, not a trend that sweeps up every form of life as it progresses.

Stewart, if I understand him correctly, argues that all species will evolve into this higher form of life, in this sense: this planetary form of life will eventually integrate all of them into a unified planetary being. This higher form of life will include even bacteria, let alone more evolved forms of life such as fish and frogs, so their evolution, too, becomes part of an overall trend towards greater complexity. In this sense, there is a single evolutionary direction which encompasses all of life. Nothing is left outside or behind.

I don't disagree with this conclusion in very general terms, and I think many other evolutionary scientists would accept it, too. That is, if humanity survives and continues its technological advances, it seems inevitable that we will bring more and more aspects of our environment under our control, to the point where we can view them, and ourselves, as part of a single higher entity. But I wouldn't say this demonstrates that evolution has an “overall” direction. I would say that one of the directions it has taken may be more sustainable in the long-run than other directions have been or will be.

In accounting for all the species that have gone extinct, or very simple forms of life like bacteria that have survived far longer than we have, Stewart says “the [overall] trajectory [of evolution] will often be masked by meandering, halting and back-tracking.” But this is an interpretation that he makes from a vantage point billions of years after the process began. We can't possibly know with any certainty that the outcome of evolution that we have witnessed so far was (like the process of biological development that he compares it to) certain, that it couldn't have halted earlier. Even at the relatively advanced stage of hominids, we know that the line that led to modern humans was at one time represented by a relatively small number of individuals, which easily could have been wiped out entirely by certain environmental conditions. There were undoubtedly many other stages along the way where the prospects of continuation were equally precarious. And even if we could establish that our highly cooperative species or something like it was inevitable, all the species that didn't get this far still represent—on the alternative interpretation of most scientists--other directions that evolution has taken.

Another way of putting this is to say that there is far, far more contingency in the process of evolution than there is in the process of biological development. Just because we can look back on our evolutionary history and see a persistent, large-scale trend towards more cooperativity and complexity does not mean that this trend was inevitable. Evolution results from the interplay of chance and selection, and while selection biases the process in certain directions, chance makes the outcome or extent of any particular direction tentative.

Regardless of how we have reached out current circumstances, however, we do appear to be in the process of creating a still higher form of life, somewhat analogous to an organism, but far more complex, and encompassing processes all over the earth. This raises a question that I want to discuss here: how inclusive is evolution now becoming? Stewart clearly believes all species that survive well into the future will do so only by integrating themselves closely into a new planetary form of life. This is essential to his thesis of an overall direction to evolution. Here I will identify some problems or at least qualifications associated with this view.

Surviving on the Outside

Stewart, like others who reflect on evolution, recognizes that one of the most serious challenges to the notion that the process has an overall direction is provided by bacteria. These relatively simple unicellular organisms have survived for billions of years, and show no sign of becoming extinct any time soon. Indeed, their survival on earth seems far more assured than our own. While we now critically depend on other kinds of multicellular organisms for our existence, some forms of bacteria could survive in the absence of any other living things.

However, Stewart believes that their future existence will be critically dependent on our own. In Evolution's Arrow, he says:

In the long term, bacteria are likely to participate successfully in future evolution only to the extent that they are incorporated into larger-scale cooperative organizations…The bacteria that will be successful in evolutionary terms will be those that become part of this planetary organisation, and that continue their membership as the organisation expands over even wider scales of space and time. (pp. 152-3)

One way to understand why bacteria have survived to the present day is because they are, and always have been, members of large-scale organizations. Even before humans appeared on earth, there was Gaia, a complex system composed of bacteria, eukaryotic cells and multicellular plants and organisms regulating the temperature, oxygen content, salinity and other parameters of the oceans and the atmosphere. Bacteria helped to create this system, even as they adapted to survive in it. More generally, any unicellular or multicellular organism survives only by interacting with other forms of life, in the process helping to create the environment it lives in. So in an important sense, bacteria have always been members of a larger organization.

Stewart's point is that bacteria will survive in the future only to the extent that they join larger, more complex organizations involving human beings, enabling them to become an integral part of a long-lasting planetary form of life. Some strains have already accomplished this, as exemplified by nitrogen-fixing bacteria in the roots of legumes, and the hundreds of species of bacteria that colonize the human colon. Stewart suggests that in the future we will intentionally create such symbiotic relationships, by managing bacteria (and multicellular organisms) for our own ends, just as we now manage certain plants as crops and certain animals as livestock. Undoubtedly this will occur. For example, there are attempts now to develop strains of bacteria to clean up oil spills, and given that disposal of waste becomes an increasingly greater problem as human populations grow in numbers and complexity, bacteria will probably be developed to play other types of clean-up roles as well.

But unless humans control and integrate all species of bacteria (and fish, frogs, and everything else), Stewart's argument fails. If some bacteria continue to live in various environmental niches, not exploited by human beings, then they remain—by Stewart's own definition-- examples of relatively simple forms of life that have survived without becoming part of a more complex organization. So Stewart's claim of an overall direction to evolution hinges on, in effect, total human domination and control of every living process on earth.

I think it would be quite possible for a unified planetary organism to emerge that fell well short of this ideal. Indeed, we have not even identified every form of life on earth, and perhaps never will. Even assuming we do, and are able to monitor them carefully, I can imagine that as long as a particular species did not seem to threaten our existence or that of the planet, we would let it continue to exist as it had. Indeed, we have of course had many lessons in the dangers of trying to control other forms of life, of trying to improve the results of genetic evolution.

Stewart might argue that eventually humans will leave the planet and colonize other planets. In the process, any forms of life, bacteria or otherwise, that have not been tightly integrated into our existence will be left behind, and will become extinct when the sun finally runs out of nuclear fuel and dies. But this event, as inevitable as it seems, will not occur until hundreds of millions of years in the future, at a time when it is far from certain our own species will still survive on other planets. Moreover, bringing the possibility of human colonization of other planets into the discussion raises another problem with the notion of an overall direction of evolution. I will discuss this later.

Limited and Full Partnerships

Even if humans did in fact succeed in bringing every single species on earth under their direct control, one can question whether this really makes these species part of a higher form of life. Consider those species, such as crop plants and livestock, that we currently manage for our own benefit in this way. Would we say that they are part of a higher form of life, human societies? Certainly not in anything like the way we are. In fact, the role that managed creatures like farm animals play in our lives is in many cases not much different from the role wild animals played in the lives of our ancestors. We raise cattle, hogs and chicken for food, whereas we used to hunt animals like deer, wild boar and grouse or quail. Some people, even in developed countries, continue to live off wild animals in this manner. The only difference is that farm animals provide a more reliable source of food.

Does Stewart really mean to say that this greater reliability makes managed livestock part of a higher form of life, whereas wild animals were not and could not be? He might respond that even back in the days when we were hunter-gatherers, a higher, planetary form of life was very slowly developing, as we gradually began bringing other organisms under our control. But to say that is to put the perspective back to where any form of existence that interacts with other lifeforms is by definition part of a larger organization or higher form of life. Then every organism, even those that became extinct, was part of this higher form of life, and therefore all of evolution was directed towards this higher form of life. Evolution of any kind by definition has a single, overall direction, which makes this concept of an overall direction so certain as to be meaningless.

In other words, we need a more specific definition of a higher form of life; it is not enough to view it as cooperation of different lifeforms, since lifeforms have cooperated in some sense from the very beginning of life on earth. I think an important idea missing in Stewart's analysis is that cooperativity only becomes a powerful evolutionary factor—one that promotes not simply survival but greater complexity—when it occurs among a homogeneous population of cells or organisms, i.e., a single species. Human societies are enormously complex because they result from the great variety of interactions that human beings can make with one another. In the process, each individual member of the society also becomes more complex.

Thus we are far more intelligent than our hominid ancestors. Of course this is related to our larger brain, but evolution of the latter was undoubtedly closely associated with an increase in number and complexity of social interactions. Moreover, even after Homo sapiens, or anatomically modern humans evolved, an enormous amount of further evolution occurred and continues to occur, precisely because of our cooperative interactions with each other.

In contrast, while other species can and have been integrated into our societies, they do not become more complex as a result. Farm horses are not noticeably more intelligent than wild horses, and dogs are probably not significantly more intelligent than their wild ancestors. To put it in the terms I have discussed in "Evolution's Quiver" and other places, there is an increase in dimensionality of individual members of a society as the society itself increases in dimensionality, but there is not an increase in the dimensionality of other species that may in some way interact with that society.

We can see the same principle at work within organisms. As noted earlier, our large intestine is home to hundreds of different species of bacteria, which enjoy a well-developed symbiotic relationship with our digestive system. These cells are so well integrated into the gastrointestinal environment that they might be regarded as cells of our body. But they are in most respects very different from our body's cells, not sharing the same genome and in fact not having any of the key features of eukaryotic cells. And likewise, they do not experience any increase in dimensionality as a result of their integration with human cells. Their interactions with the environment are limited to the same general types found in bacteria that live outside the human body.

So the integration of other forms of life into a planetary organization that Stewart envisions involves a significantly different kind of cooperation from that which has resulted in increased complexity throughout evolutionary history. While our management of other organisms and even bacteria may increase the stability and survival of a unified planetary form of life, these other forms of life do not contribute—that is, are not essential—to the process that makes this unified form higher than what came before it, nor do they themselves benefit from the increase of complexity its emergence brings about. In this important sense, they are not full members of a higher form of life. They continue to play the more limited role they played in the past.

The Role of Limits in Evolution

Stewart might nevertheless argue that a planetary form of life exhibits an unprecedented degree of unity. At its fullest development, it is the kind of unity that emerged when the first cells evolved from molecules, or the first organisms evolved from cells. The function of every form of life on the planet, even if its role is relatively simple and not much changed from the past, is now directed towards the growth and preservation of this unified being—or at the very least, is tolerated because it does not harm or threaten the existence of this unified being. Surely we can at least say that this is now the dominant direction that evolution will take from now on?

Yes and no. If we confine our view simply to the earth, evolution at this time will have brought all living processes together to a degree never previously achieved. But Stewart's view presupposes that at this point we look beyond the earth, considering the possibility that evolution may be occurring elsewhere in the universe. If it is, then the question of an overall direction is raised again. How do we know that processes on other planets will result in highly intelligent organisms like ourselves, and ultimately a unified planet?

To appreciate the situation, it's helpful to recap briefly our evolutionary past. When cells evolved, in the primordial oceans, there was a vast reservoir of space and resources. As a result, they were able to differentiate into a variety of types, proliferate, and begin competing with each other and with more primitive forms of existence. During this period, which extended up to perhaps five hundred million years ago, cells comprised the leading edge of evolution, particularly eukaryotes when they appeared.

A cell unifies all or most of the molecular processes that preceded it, bringing them together into a larger, cooperative entity. Yet we would not describe a cell as resulting from an overall direction of evolution at the time, because there were many different kinds of cells if varying degrees of cooperativity and complexity being formed, all competing with each other as well as with bacteria and perhaps proto-cells of various kinds. At this point in time, it would be more accurate to say that evolution was branching out in many directions.

A similar process occurred when multicellular organisms evolved. Different species emerged, they reproduced themselves, and began competing among themselves. An organism, like a cell, results from cooperation of the lifeforms that preceded it, in this case cells, unifying them into a new form of life. But again, it's problematic to say that any particular species of organism constituted the overall direction of evolution, because so many different species were evolving, all competing with each other and to some extent with individual cells.

Thus we can say that while both cells and organisms unified the various forms of life that preceded them, their evolution resulted in many branches or directions. This occurred because of the relatively vast amounts of space and resources that supported large populations of competing organisms and cells. No single cell or organism could predominate in such an environment.

Today, however, we are very much aware that we are approaching the limits of space and resources, as we require more and more of both to sustain our population of billions. So if a higher form of life emerges, with a unity analogous to that previously achieved first by cells and later by organisms, it will by definition be one of a kind. There is only room on the planet for one such form of life. Thus it will have to include within its organization in some manner or another all other forms of life on earth. This contingent situation resulting from limited space and resources—rather than simply a single evolutionary direction-- is what makes possible an all-inclusive form of life.

But once we turn our attention to the universe beyond, these limits may dissolve. Our developing planetary form of life might be just one of many in the universe, some of which we may eventually be able to contact and interact with. We might find it not to our advantage—or simply beyond our capabilities—to attempt to incorporate this life into our own planetary organism. Or we might simply leave it alone as an experiment in evolution. If a large number of such planets bearing life existed, it's likely they would be at different evolutionary stages, and also quite possible that some of them would never evolve to produce intelligent forms of life like ourselves. In this case, we could no longer say that our planetary being represented the overall direction of evolution. It might be the leading edge, but we would have to accept the fact that evolution did not inevitably lead to highly intelligent organisms like ourselves, and then beyond, to a unified planetary organism. It's also possible, of course, that evolution on some other planet resulted in a form of life beyond our own, and which did not attempt to incorporate our own planet into its existence.

Stewart would probably argue that any planet where life emerged would, given enough time, evolve to some state like that now existing on our earth. Or that if it didn't, our own species would create the conditions for this to occur. But of course we have no way of knowing either of these things for certain at this time (future observation of life on other planets might ultimately resolve such issues). While the arguments he provides in Evolution's Arrow suggest that such further evolution might occur, in the final analysis, these arguments are simply post hoc explanations for why evolution has occurred on our planet in the way it has. They can't be accepted as proof that this would always be the case.


As I suggested earlier, my differences with Stewart are relatively minor, and in this case may be somewhat semantic. I prefer to say that evolution has a leading edge rather than an overall direction, because the former term allows for the possibility that evolution has in the past and may in the future go in several if not many different directions. As long as there is a unifying process, in which evolutionarily advanced forms of life not only cooperate among themselves to create a higher form of life, but incorporate and integrate within this higher form of life other living things, then there will always be a tendency for evolution to be highly inclusive. And whenever there are limits that confine life to a particular space, as there are now on earth, then evolution may become more or less all-inclusive. The higher will not only include, in some sense, lower forms of life, but in these limiting circumstances, all of the lower forms of life. It is in this limited or contingent sense that Stewart can speak of an overall direction.

If there are ultimate limits to the universe, then perhaps in some distant future a single complex form of life, probably far beyond our individual comprehension, may evolve. In this case, Stewart's thesis might to some extent be ultimately validated. But I think it's important to keep in mind that this thesis is built on a retrospective approach, in which one views the currently most advanced evolutionary state and then argues that evolution must have been directed towards this state all along. If evolution were to begin anew, either on earth hypothetically or on some other planet in reality, we don't know that the cooperative processes Stewart discusses would have created a situation something like what we experience now. We also don't know for sure that evolution will continue much beyond where it is now on earth, either here or on some other planet.

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