The Major Transitions in Evolution
This last year, having completed work on the systems science textbook, I have immersed myself in the emerging and growing literature on this subject. Evolution as used here refers to the universal dynamic of change, specifically the increase in levels of organization and complexity1 over time (McIntosh, 2012; Morowitz, 2004). I devoted an entire chapter to the phenomena of auto-organization and emergence as underlying the process of evolution involving selection, descent with modification, competition, and cooperation. The latter was covered in the following chapter (the two chapters form a unit section titled Evolution). My co-author and I sought to present the concepts in the most general forms possible, as applicable to all levels of organization in the universe. The reason is that there is emerging a general understanding that evolution is much more than just the neo-Darwinian biological paradigm that has dominated thinking and investigations for the past hundred years or so. The theories of evolution have been evolving! One of the most exciting discoveries (still somewhat tentative but gaining evidence) contributing to this evolving understanding is that evolution itself has been evolving! That is, as new levels of organization emerge, the mechanisms of evolution within the new level seem to be accelerated compared with what came before. For example, I have already written about the new thinking about evolvability and how it may have played a role in the survivability of mammals and birds after the Cretaceous-Paleogene (K-Pg, formerly the K-T) mass extinction event. Over the past several decades considerable work has shown that evolution in all its forms is far more complex, subtle, and operates in levels of organization just as the physical universe is evolving into more complex, subtle, and leveled organization due to evolution. The philosophical implications are deep.
The emergence of higher levels of organization is now recognized as a sequence of transitions that occurred as a result of increasing complexity within the Universe. That means that as the complexity at any one level of organization reached a critical point in complexity of structures and functions (e.g. when proteins and nucleotide polymers were sufficiently large and interacted in autocatalytic cycles and were associated with bi-layer fatty acid complexes — membranes) many of these structures/functions combined to create new super-structures with new super-functions that, in effect, created a whole new level of organization (formation of protocells). Figure 1 shows a summary of the major transitions where higher complexity emerged from lower levels in the hierarchy (Calcott & Sterelny, 2011; Maynard Smith & Szathmáry, 1995).
Figure 1. A summary of the major transitions leading to levels of organization in the evolution of the Universe. The presumptive “Big Bang” is thought to be the origin of ordinary mass and energy. Nucleons evolved through the interactions of gravity and nuclear fusion processes in supernovae explosions. Once the Universe cooled sufficiently for stable atoms to interact within nebular clouds and in the form of formed mass bodies such as planets (like the Earth) chemical reactions led to a large variety of molecules and crystalline structures. The combinations of atoms created more complex structures that could then further interact in a pre-biological evolution of precursors for life.
At each level in this summary we see that the complexity of structures that auto-organize increases as we go up the hierarchy. For a more complete explanation of the process of auto-organization, emergence, and evolution of complexity, please see my working paper, “Does Evolution Have a Trajectory?” Here I am more interested in what that trajectory looks like, standing back and looking at the whole of the history of the Universe.
Figure 1 illustrates what we mean by levels of organization and the blue dashed lines represent the transitions from a lower level to the next higher level. For example pre-biotic chemical evolution involved the generation of the major molecular constituents of life from non-organic sources. The origin of life problem is far from solved in detail, but the broad outlines of what compounds needed to be synthesized in advance of protocell organization is understood well enough to be confident in saying that the pre-life conditions could create a milieu in which further auto-organization of those component parts led to protocells with heritable, stable genetic material and the triggering of neo-Darwinian evolutionary mechanism. The latter increased the rate of increase in complexity above what had been the case in all time before (see Figure 2 below). And eventually, with the emergence of chromosomes and stable energy-gradient consuming metabolisms, true cells (e.g. eubacteria) organized and set off a new level of evolution.
Notice a few interesting dynamics indicated in Figure 1. The obvious (red arrow pointing upward) is the increase in complexity with the increase in levels of organization. But there are two other very intriguing dynamics we should note. The first (green arrow pointing up) starting in biological evolution continues upward. This is to recognize that the emergence of social evolution (cooperation among biological entities to give rise to higher organisms) did not actually bring biological evolution to a halt. Biological evolution, however, is seen as halting any chance for pre-biotic developments. The reason given is that bacteria, especially, would instantly consume any non-organic but carbon-based molecules that might form by accident. So the chance that a second or third pre-biology could get a hold is essentially nonexistent. This is similar to the slowdown and cessation of nucleonic evolution due to the limits of energies needed to fuse ever more complex nuclei. The depletion of lighter weight elements in making heavier elements simply acted as a negative feedback to bring further evolution to a halt.
Social emergences and evolutions (e.g. endosymbiosis giving rise to eukaryotes, colony cell specializations giving rise to multicellular forms, and higher forms of social organizations) did not halt biological evolution, but instead enhanced it (Bourke, 2011). But then we get to cultural evolution, and in particular that of human cultures, which especially includes science and technology. Suddenly we see a re-triggering of lower level evolution due to human intervention. We have generated nuclei we don't (or haven't) find in nature. We have created chemical compounds impossible to auto-synthesize in nature. We are on the verge of creating artificially constructed protocells and even cells. We have cloned all kinds of creatures that would not have happened in natural selection. We have created chimeras from multiple species. It seems as if humans and their scientific cultures have restarted the lower levels of the complexity hierarchy and we have yet to see what may come of further evolution taking place in those levels. Most people look with great horror on this development, claiming we are creating monsters that will destroy us. They may be right. But there is another (non-humanistic, but perhaps more objective) way to look at it. We are simply unwitting agents in the Universe's once-more increase in the rate of evolution of complexity. We are the Universe's way to increase its own evolvability. We, as a species, may be victims of this transition. But the Universe as a whole may actually achieve a whole new level of organization as a result.
Figure 2 is a very rough approximation of the rate of increase in complexity as a result of Universal evolution. It looks exponential. A central question raised by this view would be, how much more complexity is possible? The answer may lie in realizing that the perspective shown in Figure 2 is from us residing on this planet. Change the scale, by stretching the time line out many more billion years into the future and the complexity measure up by many orders of magnitude and the steep rise we see from Earth might just look like a slower sloping exponential (still). In other words, we can't let our earth-bound and species-centric bias influence our perspective on what evolution is really all about.If we can help it.
Figure 2. Overall complexity of the Universe appears to have grown at an exponential rate (albeit very small exponent). This is a very rough graph that shows how levels of organization emerged and the evolution of complexity then appears to have greatly increased. Other authors have suggested that the graph should depict a step function as the emergence phase might have been rapid and the evolution phase slower.
Auto-organization, the emergence of new levels organization, and the evolution of structure and function with those levels depends entirely on the flow of energy. Energy flowing from a high potential source of the right kind of kinetic form to a low potential source powers the processes and their adaptation (maintenance of function in spite of environmental variations) and evolution (changes in form and function to maintain continuity into the future) over time and space. The sun has been the main source of high powered energy flows in the form of electromagnetic radiation (light). Early life may have used less powerful chemical potential gradients to extract energy but once photosynthesis was discovered the power of light was exploited to synthesize new structures and perform new functions (of course life based on chemical energy sources can still be found today, for example at thermal vents in the deep ocean). The evolution of life has since largely been driven by the steady flow of energy to the earth from the sun and the eventual degradation of the energy to waste heat due to the many work transformations done by the biosphere.
Life evolved us. We and our late progenitors found new ways to raise the level of organization above that of life itself. Through the evolution of our large brains we became capable of invention of artifacts that allowed us to exploit sources of solar energy other than food. We gave rise to a new complexity — humans and artifacts that would then evolve together, that is co evolve. The artifacts increased human access to high powered energy flows which then allowed humans to gain greater ecological fitness in a much higher number of environments. Even though some people think evolution of our biology has ceased with our ascension to the top of the food chain and our technological ability to keep genetically deficient individuals alive prosthetically (e.g. glasses), in fact we are not the exact same species that emerged from Africa some 60-65 thousand years ago. Racial differences attest to the on-going force of selection for traits commensurate with different environments. This cannot be denied. So our culture(s) which made dispersion across the planet feasible has recursively acted on us to push biological evolution, albeit at a normal pace for biological evolution, further along.
On the other hand, culture has evolved at an exponential rate due to the continuing discovery of higher and higher potential energy gradients. We cannot eat hydro power, or fire, or explosions. These forms of energy conversion from potential to kinetic could not feed directly into our biological bodies to drive some kind of super-biological evolution. But they can be exploited in machines that we invented as we explored what possible ways we could exploit water, wind, animals, tree, coal, oil, and nuclear fission. These high power energies can effect our minds, inspire our inventiveness, and as a result we act as the selective forces that play the evolution of culture. With enough excess energy available our artifacts need not be only functional (practical) but esthetic as well. Indeed a whole category of artifacts are only meant for esthetics. Culture evolved rapidly because of the availability of energy and the coupling between biology and artifacts through the human mind.
This raises an unpleasant thought. If evolution depends2 of increasing availability of higher power then we face a very unusual condition in the not-so-far-off future. Fossil fuels being the main source of power now (over 80% globally) and finite in abundance are starting to be harder to extract as a result of their depletion. This is reflected in the rising costs of extraction and decreasing marginal returns on investments and production. Eventually, and I suspect within the next decade, the cost-benefit ratio for fossil fuels will simply go to one (1) with the result that the energy flows to our culture (and hence to our biomass maintenance) will fall to zero from these sources. Cultural evolution will slow to a halt and afterward go into devolution (in the best case scenario).
Of course, humans will not react well to this decline of what they had come to know as “progress.” Their reactions will more likely cause a catastrophic decline of the further coevolution of mankind-cultures leaving whatever is left of the former with naught but the stone tools of our fore bearers of some fifteen thousand years ago.
At first glance this would seem to go against the picture of evolution producing ever higher levels of organization in these major transitions. From our perspective this looks like an end of evolution rather than a transition to higher evolution. But that is just from our perspective. Had the dinosaurs been at all sentient and knew something about progress they would have surely thought their extinctions would have been an end to the emergence of higher levels of organization. After all they were the norm. To their way of thinking they probably could not imagine the world going on without them. Wouldn't progress have simply meant more diversity in dinosaur species?
But while a power reset to a lower value will degrade cultural evolution in its current form, it does not follow that all of humanity is lost. The bulk of human biomass does depend on technology to keep it alive. Without modern agricultural industry, more humans will go hungry and starve to death. Others will act violently to save themselves as best they can. However it is not a given that all human life will come to an end. There is some non-zero likelihood that some humans will survive and figure out how to maintain in spite of the collapse of societies and the radical climate changes that are ahead. Human beings are, after all, enormously adaptive. And all that is needed to provide the future basis of continuing biological and “mental” evolution of the genus Homo is a high capacity to adapt.
An Impending Transition
When considering some of the conditions prevailing prior to previous transitions it is intriguing to realize that most were in response to heavy stresses acting on components that would eventually combine to create the new structures at a new level of organization. In other words, the emergence of a new level, and the mark of a transition, were a result of strong selection against components but for combinations that were more adaptive than any one component by itself. Synergy is the result of components acting cooperatively to accomplish what no one, or even the aggregate of components, could do alone. Though much research must be done to validate this, a picture has been developing of the fortuitous symbiotic relations that developed between prokaryotic cells that gave rise to the eukaryotic forms. The process has been termed “endosymbiosis.” There is a suggestion that larger prokaryotes ate smaller ones but failed to digest them and they stuck around, having found a suitable safe haven. We don't know exactly what the conditions were for some large prokaryote to engulf, say the precursors of mitochondria or chloroplasts (plastids that retain a significant working genome of their own), but we do know that relations between all of those precursors could have developed gradually and probably proceeded through a colony-like association before actual internalization. Mitochondria precursors, for example, might have supplied large eubacteria colonies with ATP supplements to their chemoenergy sources. Also what we know is that mutualistic relations develop between species when there is an advantage to cooperate and that such an advantage increases the fitness of both. And, finally, we know that such relations will be selected for even when there is negative selection operating on the individual members of one or the other species.
The growing abundance of free oxygen in the atmosphere and hydrosphere was just such a dramatic and increasing selective force. Respiration requires oxygen to “slow burn” carbohydrates to release energy packets able to supply synthesis machinery (e.g. ribosomes). Oxygen also kills anaerobic bacteria quite nicely so selection for oxygen tolerance was quite strong. It would have been greatly increased by the inclusion of a nice little bug that could fix oxygen to carbon and hydrogen while producing wonderful little batteries for use by other organelle (also likely prokaryote derived).
The transitions seem always to involve the evolution of sociality3. The new level of organization always involves the new kinds of interactions between socialized new forms. Molecules can undergo chemistries that atoms by themselves are incapable of. For example, protein catalysts (enzymes) are able to facilitate so many difficult reactions (with large energy hurdles) that no single atom, or even small molecules, could manage. The chain of amino acids in an enzyme cooperate by forming complex shapes that have kinetic properties suited to perform their collectivized function.
Even the origins of human sociality on the plains of Africa seems to have been in response to strong selection forces. Humans gave up claws and jaws in favor of posture and voice. They were no match for the carnivores of the environment. They were not even built well for being carnivores. They needed to evolve social mechanisms to support acting as a unit for hunting, gathering, protection, etc. The stresses of climate and competition acted to select those groups of humans (tribes) that best cooperated within the group. They were in competition not only with other species, but with conspecific tribes as well. The ones that did the best job of intra-group cooperation won the competition.
The reduction in the power available to human culture may mean an end to the kind of culture we have become used to. But it does not mean an end to human evolution. As long as there is sunlight some humans can and will survive, even thrive. But the stresses of survival in the brave new world could easily mean that the evolution of a new, greater level of socialization is in the offing. Current human culture represents what amounts to the first baby steps toward the kind of eusociality previously accorded to species like ants and naked mole rats. Our role in this transition to a sentient form of eusociality is merely as a transient species having some of the characteristics of both a semi-social (e.g. other apes) and a eusocial species. The latter is evidenced in the fact that we can, under nominal conditions, form strong cooperative associations even with strangers to accomplish some common goal. Evidence of the former is the level of cutthroat competition, selfishness with profits, and greed that are displayed by too many of our kind today. This is our ancestral reptilian brain at work. The cooperativeness that we display in our near eusociality is the result of our neocortex and particularly the large prefrontal cortex (orchestrated by the patch right behind the eyebrows called Brodmann area 10). We are the transition.
Humanity finds itself in the same kind of predicament early life (anaerobic bacteria) faced when those devilish little blue-green algae (actually cyanobacteria) started defecating oxygen! The impending stresses from reducing power flows and increasing climate changes promise to put us in dire need. We have to evolve or go extinct.
A Blessed Bottleneck
Transition in the biosphere is coming. There is no way to avoid it. There will be another great die-off and many species will exit the stage of life. We could be one of them. But I honestly don't think we will. Rather I think the course of evolution already laid, its trajectory, will not be thwarted entirely. Our culture is not the defining property of our biological species, our capacity to build a culture based on cooperation is, however. The extent and kind of culture that humans can build will, of course, depend on the power available to them, but it is the act and process of building some culture that is the essence of our biology.
Regardless of who gets through the bottleneck event (roughians or sapients) I'm not sure it will make a difference. The forces that will drive the evolution of future species of Homo, I conjecture, will favor greater cooperation not less. Furthermore, the brain structural seeds of circuits that will support cooperativity are already sown. As future generations experience mutations that improve those circuits they will differentially succeed in the competition with poor cooperators by building adaptive cultures that can deal with the contingencies of the future.
The history of universal evolution is one of transitions to greater cooperativity (sociality) reacting to increases in stresses at lower levels. Think of it like what Per Bak calls self-organized criticality. A pressure builds up in a non-linear complex system. Mostly small evolutionary events occur. Every once in a while a middle sized event (e.g. origin of a new genera or loss of an old one) occurs. And on very rare occasions a really large event, a transition event, takes place, and nothing is the same afterward. I think this is where we are headed.
Do not weep for humanity friends. We are just players in a universal drama. It is a story of redemption even if the protagonist dies. Sentience will continue up the curve in Figure 2 for a ways more. It can happen not by increasing cultural complexity per se, but by raising the social complexity bar. After the transition (say ten thousand generations from now!) the cultural + social complexity can once again increase. Power alone is not the only thing needed for post-transition complexity. Mind, sentience, cleverness mediated by sapience is the key. Eusapient beings in that distant future may discover new sources of power to drive artifact complexity once again. But they will not be lured into creating complexity for its own sake (novelty and convenience). Nor will they be so foolish as their predecessors (us) to waste their environment in pursuit of that kind of complexity.
How Could Anyone Know What Will Come?
No one does, of course. I am speculating, to be certain. But consider this. The major patterns of universal evolution are becoming clear to us. Those patterns repeat themselves in different forms, but systemically they are the same. Competition drives inter-specific and conspecific incremental evolution. Cooperation emerges in response to the build up of competition-based and environmental forces (like climate). I have no idea what the details might look like, but I think I can see a broad picture emerging that gives me considerable hope. And joy. Humans in our current form will absolutely go extinct eventually. But, if I am right, it will be the death of a species giving birth to a new species that is more fit in the context of the planet as a whole system. It would be sad indeed if the extinction of Homo sapiens was the end of sentience on this planet, given the potential for that sentience to rise above mere sapiens' cleverness. It is certainly one of the outcomes possible but it would seem to me to have been such a waste of time and resources. Evolution has a history of purchasing new opportunities on the expenditures of prior species, genera, and higher. It has inexorably led to greater information/knowledge processing and complexity of organisms throughout its history. Why would it not be so in the future?
Indeed, as long as the sun produces an energy flow commensurate with life (light energy) there is still time for evolution to produce a much more highly capable sentience than are we. There is no law of nature to prevent it. We won't be able to know what that sentience looks like (humanoid presumably). But I think we can take comfort in knowing that if it exists it will be the new and better us.
Bourke, Andrew F.G. (2011). Principles of Social Evolution, Oxford University Press, New York.
Calcott, Brett & Sterelny, Kim (2011). The Major Transitions in Evolution Revisited (Vienna Series in Theoretical Biology), The MIT Press, Cambridge MA.
Maynard Smith, John & Szathmáry, Eörs (1995). The Major Transitions in Evolution, Oxford University Press,
McIntosh, Steve (2012). Evolution's Purpose: An Integral Interpretation of the Scientific Story of Our Origins, SelectBooks, Inc.
Morowitz, Harold J. (2004). The Emergence of Everything: How the World Became Complex, Oxford University Press, NY.
Sawyer, R.Kieth (2005). Social Emergence: Societies As Complex Systems,Cambridge University Press, Cambridge UK.
Simon, Herbert (1996). The Sciences of the Artificial, 3rd ed. MIT Press, Cambridge MA.
1. Complexity as used here refers to an indexed value based on the depth of the hierarchy, after Herbert Simon (1996). As components form stable complexes at lower levels, new interactions between those complexes emerge and new laws of organization take shape. This forms a hierarchy of realized complexity. The depth of the hierarchy (as shown in Figure 1) provides a measure of complexity.
2. And here I include the effects of population growth as part of the equation of evolution because larger populations support a possibly higher variability in genetics and ideas, thus the fitness of mankind plus culture has to lead to higher reproductive success for all!
3. Sociality is the term being applied to all forms of cooperation taking place at all levels of organization in the complexity hierarchy. Atoms are social in combining to make molecules. Molecules are social in combining by various bond forms to create complex shapes (like enzymes). Cells are social when the communicate with one another and form tissues, and so on.