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John StewartJohn Stewart is Core Member of the Evolution, Complexity and Cognition (ECCO) Research Group, The Free University of Brussels, Belgium. His work on the directionality of evolution and its implications for humanity has been published in a number of key papers in international science journals. He is the author of Evolution's Arrow: The Direction of Evolution and the Future of Humanity (2000) and The Evolutionary Manifesto.

A Wider Perspective on Evolution

Does The Persistence Of Bacteria, Frogs and Fish
Mean That There Is No Overall Direction to Evolution?

John Stewart

This long sequence of directional evolution has been propelled by the potential for cooperative organizations to be more successful than isolated individuals.

In two recent essays, Frank Visser (Some Paradoxes of Evolution) and Andrew Smith (Evolution's Quiver) argue that evolution lacks any overall direction. Visser and Smith observe that significant groups of organisms do not appear to have evolved in any general direction for millions and in some cases billions of years. Bacteria are the most obvious example: they have continued to exist as relatively simple, single-celled organisms in huge numbers across a wide variety of environments for well over 3 billion years. Other examples include the many species of frogs and fish that do not seem to have evolved in any particular direction for millions of years.

Visser and Smith also observe that so-called 'advanced' species have not replaced simpler, earlier ones. Bacteria, fish and frogs continue to survive and thrive along side organisms that have climbed further up the supposed ladder of evolution. As Visser asks:

why is it that species and even whole phyla remain in existence, even when evolution has "moved on"? Why didn't all fish become amphibians? Why didn't all amphibians become reptiles? Why didn't all reptiles become mammals? And so on: why didn't all chimpanzees become human beings? What was holding them "back"?

Surely this widespread and sustained absence of directional change means that evolution has no overall trajectory? And surely the continued survival and success of organisms that haven't changed means that they are not somehow inferior and “less evolved” than those that have?

In this essay I will set out to demonstrate that the apparent absence of sustained directional evolution in many groups does not imply a lack of overall direction. I will show that if we stand further back from the history of life on Earth so that we can see past, present and future evolution as a whole, and if we take into account large-scale processes that have begun to emerge recently and that are likely to continue strongly into the future, we will see an unmistakable overall direction.

It is difficult to detect the overall direction of evolution without this much wider perspective. It is a bit like looking at a developing chicken egg, and focusing closely in on some of the specific processes within the egg for short periods of time. In many cases, it would not be evident that the particular processes are headed anywhere in particular. It is only when all the processes of the developing embryo are considered as an integrated whole over a longer time frame, that it becomes abundantly clear that there is an overall trajectory to the developing egg.

I will begin by putting together a broad understanding of the past, present and future evolution of life on Earth. This wider perspective will then be put to use to show that the evolution of bacteria, fish and frogs is part of the overall trajectory of evolution, and in no way contradicts its existence. Properly interpreted and understood within the wider perspective, the evidence confirms that evolution is fundamentally directional.

First I will focus on a particular large-scale pattern in the evolution of life on Earth: as evolution has unfolded, an increasing proportion of living processes have been progressively integrated into cooperative organizations of larger scale and greater evolvability (evolvability is the capacity to discover effective adaptations. At the human level, intelligence is a component of evolvability). This trajectory began with the formation of the first simple cells (including bacteria) from cooperative organizations of self-replicating molecular processes. Then cooperative groups of some simple cells formed the more complex eukaryotic cells that make up our bodies. Some of these complex cells teamed up to form multi-cellular organisms (including worms, fish and humans), and cooperative organizations of some multi-cellular organisms formed animal and human societies (including bee hives, termite colonies, and baboon troops).   

The evolution of human societies shows a similar pattern. Humans have been progressively integrated into social organizations of increasing scale: from family groups to bands, to tribes, to agricultural communities, to city states, to empires, to nations and so on.  Whether evolution proceeds by gene-based natural selection or cultural processes, the result is a clear trend amongst some living processes to form cooperative organizations of greater scale and increased evolvability.

This unmistakable trend is the result of many repetitions of a process in which living entities team up to form larger-scale cooperatives. Strikingly, the cooperative groups that arise at each step in this sequence become the entities that then unite once again to form cooperative groups at the next step in the sequence.

The next step in this trajectory is obvious: the emergence of a cooperative organization of living processes on the scale of the planet. All of humanity and all human organizations would be integrated into this sustainable global civilization. But humans would not be the only species incorporated into the new global entity. So too would the other living processes of the planet. Humans have a long history of integrating other organisms into its organizations. Humans are farming, managing and controlling an ever-increasing proportion of the organisms on Earth. As a planetary civilization emerges, humanity will begin to manage a global symbiotic organization that comprises the matter, energy and living processes of the planet, including machines, artificial intelligence and other technologies.

When this global system emerges, the scale of cooperative organization will have increased over a million, billion times since life began as tiny, self-replicating molecular processes. And life on Earth will constitute a cooperative and interdependent entity that embraces the planet.

The causes of the progressive integration of living processes into larger-scale cooperatives are not a mystery. This long sequence of directional evolution has been propelled by the potential for cooperative organizations to be more successful than isolated individuals. Whatever the evolutionary challenges, living processes can respond to them more effectively if they form cooperative organizations and if their actions are coordinated. In part this is because cooperation enables the exploitation of synergies, including through specialization and division of labor. In addition, the larger the scale of any cooperative organization, the more resources are commanded by it, the greater its power, the larger the impact and scale of its actions, and therefore the wider the range of environmental challenges that it can meet. These potential benefits of cooperation are a powerful driver of further integration at all levels of organization, whether we are considering self-replicating molecular processes, complex cells, organisms, corporation or nations. Cooperation is more competitive and therefore fitter. As we shall see, cooperators will inherit the Earth. Eventually they will inherit the universe.

Importantly for the argument I am advancing here, the potential benefits of cooperation are universal, and therefore tend to drive universal directionality. No matter what the species (or group of species), no matter what the local circumstances, the members of a species have the potential to utilize energy and other resources more effectively if they cooperate and if their activities are coordinated. Consider members of a group that specialize in different activities and then share the benefits of their greater efficiency. Potentially they will be more effective than individuals who each carry out all functions themselves, specializing in none. Directional evolution can therefore occur even when evolution acts only locally and immediately—i.e. when it favors only features that are of immediate benefit to each organism in its local circumstances. Cooperation is potentially beneficial to all organisms, no matter what their circumstances.

The trajectory towards wider cooperation will often be masked by meandering, halting and back-tracking, particularly when the process that searches for improvements relies on blind trial and error.

But universal potential does not guarantee directional change that is continual and universal. The trajectory towards wider cooperation will often be masked by meandering, halting and back-tracking, particularly when the process that searches for improvements relies on blind trial and error (e.g. gene-based natural selection). The trajectory will also stall on occasions because cooperation does not evolve easily. Cooperation can emerge only when complex arrangements are in place. This is because individuals who cooperate will generally be outcompeted by selfish free-riders who accept cooperation from others but give nothing in return. It is only in the evolutionary interests of individuals to cooperate when it pays them to do so. So if cooperation is to be favored by evolution, complex arrangements need to be in place to achieve this. These arrangements need to ensure that individuals benefit from their cooperation, and also need to suppress free-riding. This reconciles self-interest and cooperation by aligning the interests of individuals with those of the group (for a detailed examination of the difficulties that must be overcome if cooperation is to emerge, see Chapters 4 to 7 inclusive of my book Evolution's Arrow). Furthermore, cooperation will only be favored by evolution when its advantages outweigh the cost of the arrangements needed to organize it. As a consequence, directional change will often stall until evolution discovers a cost/effective way to organize cooperation and exploit its potential benefits.

But this stalling is likely to be overcome eventually. As evolution proceeds along its trajectory, living processes emerge that are better able to organize cost/effective ways to realize cooperation, including by integrating other species into their cooperative organizations. This is because they are larger in scale and therefore more powerful, and they are more evolvable and therefore better equipped to discover effective ways to organize cooperation. These capacities enable them to integrate other organisms into their organizations whenever they benefit from doing so (e.g. ant colonies and humans farm other species). As noted already, eventually all living processes will tend to be swept up into a global cooperative organization. In this way, the potential benefits of cooperation will be realized progressively through the actual integration of living processes into larger-scale organizations.

Now that I have sketched the overall pattern of evolution, I will turn to showing in detail how the evolution of specific groups is entirely consistent with it. I will start with bacteria and show how their evolutionary history supports rather than contradicts the pattern. I will then do the same for fish and frogs.

The first point to note is that a significant proportion of bacteria have already evolved along the trajectory that characterizes this large-scale evolutionary pattern. It is wrong to say that bacteria in general have not evolved directionally. It is true that individual bacteria have not become more complex in themselves. But the trajectory of evolution that I have identified does not involve any overall trend towards increased individual complexity. Rather the direction of evolution is towards the progressive integration of living processes into cooperative organizations of greater and greater scale. And bacteria comprise an important part of this trajectory.

In particular, as evolution has unfolded on Earth an ever-increasing proportion of the descendents of the first bacteria have come to participate in larger-scale cooperative organizations. A key step in this direction was the emergence of the complex eukaryote cell. It arose from symbiotic communities of simpler cells, including bacteria. For example, it is now generally accepted that the mitochondria in our cells are descendents of bacteria. Through their participation in complex cells, these descendants of bacteria now also participate in multi-cellular organisms including humans, and therefore also participate in animal societies including human social systems. From this perspective, the European Union is a large-scale cooperative organization which is comprised in part of highly-organized and differentiated descendents of bacteria.

There are numerous other examples where bacteria have been integrated symbiotically into larger-scale cooperative organizations: the billions of bacteria that live in our intestine; nitrogen-fixing bacteria that live in the nodules on the roots of legumes; and the gut fauna that assist many herbivores including cows to digest plant material.

Those bacteria that have been integrated into larger-scale cooperatives have been very successful in evolutionary terms. They have taken over an increasing proportion of the energy and resources that were once exploited only by free-living bacteria. And they have increasingly found ways to exploit new sources of energy and materials across the planet.

But what about the significant proportion of bacteria that don't appear to have yet been integrated into larger-scale cooperatives? Does their existence demonstrate that there is no overall directionality in bacterial evolution?

Importantly this apparent absence of cooperative integration amongst some bacteria is not due to a lack of potential benefits that could flow from their integration. Potentially, any given population of bacteria could exploit its resources more effectively if the population was coordinated and organized cooperatively. Members of the population could specialize in particular functions or for particular circumstances, and the population could share the benefits of this. Furthermore, bacteria could potentially enter into exchange relationships with other species that would benefit both. This is because free-living bacteria exploit some energy and material resources more effectively than do other species. The widespread examples of successful cooperative arrangements amongst bacteria and between bacteria and other species illustrate the existence of these potentials.

But why has evolution failed to realize these potential fitness benefits for many bacteria? A key reason is that it very difficult to organize cooperation at the cellular level without utilizing particular forms of organization that are very limited and restrictive. These particular forms of organization are too inflexible to allow the kinds of cooperation that could exploit the potential benefits of cooperation in many situations.

We can understand the reasons for this by examining the forms of organization that evolution has used to exploit cooperation between cells. In nearly all instances, cooperating cells live in direct physical contact with each other. This is certainly the case for the communities of simple cells that formed the complex eukaryote cell, and for the groups of cells that formed multi-cellular organisms. In his essay, Smith identifies some of the reasons why cooperation amongst cells could only be exploited by these very restrictive forms of organization. Effective coordination and cooperation requires communication between individuals and exchanges of materials amongst them. It also requires a way to distinguish between members of the cooperative and others, and ideally also between different members of the group. Because of the limited communication capacities and intelligence of cells, the only feasible way in which cells can do these things in most circumstances is by maintaining direct physical contact between members of the group.

The need to maintain direct physical contact between individuals greatly handicaps the ability of a cooperative to explore effective forms of cooperation.

The need to maintain direct physical contact between individuals greatly handicaps the ability of a cooperative to explore effective forms of cooperation. Imagine if humans could cooperate with each other only by forming groups in which members continually maintained direct physical contact. Compare this with a modern corporation whose members can operate independently across the globe, specializing and exploiting resources wherever they are found, coordinating their activities and sharing resources and benefits. If humans couldn't organize cooperation and coordination 'at a distance', humanity would not be the dominant force it is across the planet today. The benefits of human cooperation would still exist potentially, but they would be largely unexploited.

So to date the capacity of bacteria to exploit the potential benefits of cooperation has been limited. They have been handicapped by inflexible organizational forms. As a consequence, cooperative organizations of cells have been unable to out-compete free-living bacteria in niches where their restrictive forms of organization put them at a disadvantage. A pervasive example is where extremely small size is needed to exploit energy and resources, such as in the tiny spaces between soil particles and even within rocks. Cooperative groups in which all members must maintain direct physical contact are too large to function effectively in niches where smaller size is essential.

It is worth emphasizing that the potential benefits of cooperation exist in these cases. The free-living bacteria that exploit resources in tiny spaces would be more effective if they were part of an organized and coordinated cooperative that communicated and coordinated its activities 'at a distance'. It is reasonable to conclude that once evolution discovers cost/effective ways of organizing cooperation in these cases, the potential benefits of cooperation will drive further directional evolution. As we will now discuss, this is beginning to happen on this planet.

Free-living bacteria are now increasingly being integrated into larger-scale cooperative organizations. This has been made possible by the emergence of organisms that are highly evolvable (intelligent), powerful and able to coordinate actions over much larger scales than bacteria—i.e. due to the emergence of humans and cooperative organizations of humans. Humans are beginning to develop the technology and know-how to manage bacteria and integrate them into larger-scale human-dominated organizations for human ends. Humanity is starting to exploit the benefits of cooperation that so far have been unrealized by some species of bacteria.

Bacteria that harm humans and human organizations are being destroyed or intentionally controlled. For example, humans are creating micro-environments that are bacteria-free and environments in which the populations of certain kinds of bacteria are greatly reduced. Bacteria that are capable of contributing positively to human goals are being supported and nurtured (just as farm animals and edible plants have been integrated into human organizations). For example, humans create conditions that support the growth of particular species of bacteria that assist the production of dairy products such as cheese and yoghurt. And progress is being made in the cultivation of certain kinds of bacteria to produce electricity and hydrocarbon fuel. The use of bacteria for human purposes is not likely to be limited to the nurturing of particular species and to the suppression of others. More sophisticated ways of using bacteria for human ends are likely to involve the promotion of positive symbiotic relationships amongst bacteria as well as between bacteria and other species, including using genetic engineering.

But more significantly for the integration of bacteria into large-scale organizations, humanity is beginning to actively manage entire ecosystems and the larger-scale ecological cycles and processes on which human survival depends. Bacteria play a critically important role in these systems and cycles. Human disruption of these larger-scale ecological processes will increasingly demand management of the processes and of the bacteria and other organisms that participate in them. Current attempts to regulate the amount of carbon dioxide in the atmosphere are just a small, first step in this direction.

All relevant aspects of the planet, including bio-geo-chemical cycles will be optimized for the flourishing of the global entity.

As we have seen, these trends can be expected to continue apace. Human systems will increasingly manage the energy, matter, living processes and technology of the planet into a global entity. Bacteria will be increasingly integrated into the emerging entity. The global entity will manage all the living and non-living processes of the planet to create the best-possible platform for its further development and evolution. From the perspective of the global entity, the planet's ecosystems will constitute important parts of its metabolism. The global entity will use its intelligence and evolvability (constituted by humans and artificial intelligence) to organize its metabolism for maximum effectiveness (just as DNA manages the metabolic processes within a cell). All relevant aspects of the planet, including bio-geo-chemical cycles will be optimized for the flourishing of the global entity. Eventually all the living processes of the planet including bacteria will participate in a symbiotic community that will be like an organism on the scale of the planet. Like an organism, it will be able to act as a coherent entity, with goals and intelligence of its own.

Humans are finding it useful to integrate free-living bacteria into their organizations because some bacteria can exploit particular resources more effectively than humans. The global entity will incorporate bacteria for similar reasons. As we have seen, humans are comprised in part of the descendants of particular kinds of bacteria. Despite already incorporating bacteria, humans are unable to exploit some resources in particular niches as effectively as free-living bacteria. As we have seen, this is because of the restrictive forms of organization that were used to integrate bacteria into complex cells and to integrate those cells into multi-cellular organisms. Humans are now developing the capacity to integrate free-living bacteria into sophisticated organizations that are more flexible and far less restrictive. By doing this, humans will be able to share in the superior ability of some kinds of bacteria to exploit particular resources. For example, it will enable humans to share in the advantages that some bacteria have in certain niches because of their extremely small size.

We are at the very beginning of this integration process. Humans are in the early stages of developing the technology and knowledge to integrate bacteria into human-dominated organizations. This integration can be expected to expand considerably over the coming millennia, if humanity survives.

The extent to which bacteria are tightly integrated into human-dominated organization is likely to be greatest in the organizations that are used to expand the global entity into space.[1] As human organizations move out into the solar system and beyond, they are likely to take with them a carefully-selected and tightly-managed self-sustaining ecosystem. Included in each organization will be the bacteria that live symbiotically within our gut, the descendents of bacteria that comprise our cells, as well as an ecology of bacteria and other organisms that can support and sustain human existence elsewhere.

In the long run, only the tightly-managed symbiotic organizations that move out into space are likely to survive and thrive. The Earth itself is threatened by extinction events, not least of which is the projected engulfment of the planet when the sun enters its Red Giant stage. Because of its scale and power, a human organization that manages the matter, living processes and energy of a solar system or of a galaxy will be capable of surviving the destruction of the Earth. It will be able to adapt successfully to a much wider range of events than an uncoordinated population of bacteria. It will be able to move and adapt as a coherent whole. All the participants in the organization will be adapted along with it. They will be adapted as if they had the greater intelligence and power of the organization itself.

In contrast, if any free-living, non-integrated bacteria continue to exist, they are unlikely to survive the engulfment of the Earth. Bacteria that are not perpetuated as part of human organization are therefore likely to be temporary in the long run. Eventually there will be no such thing as evolutionary 'laggards' that are not integrated into large-scale cooperative organization. The directionality of the evolutionary process will become increasingly undeniable.

The same general principles apply to other apparent evolutionary 'laggards' such as fish and frogs. Already humanity is integrating a significant biomass of fish into its larger-scale systems through aquaculture and other farming approaches. And attempts are being made (currently often incompetent) to manage more and more of the remainder through fisheries management and marine parks. Farming of frogs is currently much more limited. Their management is currently restricted in large part to unintentional extinctions and conservation activities in the form of nature parks and humanity's first clumsy attempts to manage natural ecosystems.

But as we have seen, the energy, matter, living processes and technology of the planet will increasingly be managed by humans into a global entity. Fish and frogs, like bacteria and all other organisms, will be integrated progressively into the emerging global entity. When the global entity manages and optimizes large-scale ecological processes including bio-geo-chemical cycles, it will be managing the organisms that participate in those cycles and processes, including fish, frogs and bacteria.

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. It seems that the question that he (and Visser) asks in order to test whether there is overall directionality is this: have particular organisms such as bacteria, frogs and fish become more complex and are they in the process of becoming more complex? The evidence on this is clear: many of these organisms have not become more complex, and are not becoming so. As a result, Visser and Smith reject the directionality hypothesis.

But Smith and Visser are not testing the most promising hypothesis about directionality. The key large-scale pattern in the evolution of life is towards the progressive integration of living process into cooperative organizations of increasing scale and evolvability, culminating in the emergence of an integrated and coordinated global entity. The kinds of questions that should be asked to test overall directionality are therefore: have organisms such as bacteria, frogs and fish been integrated into larger-scale cooperatives? In instances where they have not, is it beginning to happen now? Can it be expected to occur to a greater extent in the future? Is this likely to result eventually in an integrated global entity? The evidence answers these questions affirmatively, as do some of the key conclusions reached by Smith in his essay.

We are now in a position to stand back from the evolutionary process on this planet and see it as a coherent whole, integrating past, present and future. When living processes first emerged, they were very small in scale and restricted to specific environmental conditions. From there life spread, specializing and diversifying into other environments, exploiting an increasing variety of free energy and other resources that are needed to sustain it. As this unfolded, some living processes discovered ways to cooperate and to coordinate their activities, significantly enhancing their effectiveness in some environments. These larger-scale cooperatives in turn spread and diversified. But because of limits to their ability to exploit the benefits of cooperation, they were not able to utilize all resources more effectively than their predecessors, and therefore did not replace them entirely.

Some of these larger-scale cooperatives in turn discovered ways to coordinate and cooperate, thereby further increasing their effectiveness. This enabled them to spread and diversify further across the face of the planet. Some of these larger-scale entities developed the power and evolvability to integrate other organisms into their organizations, overcoming impediments that prevented the organisms from exploiting the benefits of cooperation on their own. Many repetitions of these evolutionary integrations produced cooperative organizations of greater and greater scale, leading to the emergence of a cooperative organization on the scale of the planet. Such a global entity will eventually integrate the diversified and specialized living processes of the planet into a coherent whole, enabling the global entity to exploit energy and other resources from diverse environments.

It can be seen at this point that the diversification and specialization that occurred at lower levels was in fact part of this directional process. It enabled the widest range of resources to be exploited by life. The subsequent integration of these diverse smaller-scale entities into a global entity enables the entity to exploit the widest possible range of resources across the varied circumstances of the planet.

As the global entity continues to develop, it increasingly manages the living processes, energy, matter and technology of the entire planet into a coordinated whole, and optimizes all the processes on which it depends (including large-scale ecological cycles) in order to create the most effective platform for its future evolution. Of course, this is not likely to be the end of the evolutionary trajectory. The trajectory is likely to have unfolded elsewhere (although the details are likely to be different), and similar diversifications and integrations are likely to be repeated at larger and larger scales across space and time.


[1] Of course, a global entity could attempt to reproduce in places that are not accessible to human-dominated organizations by seeding them with simple cells. Given sufficient time and suitable circumstances, the trajectory of evolution described here would tend to eventually produce a global entity. It is possible that life on Earth is the product of such a reproductive strategy.

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