There’s nothing like a good sparring match among evolutionists. The skeptic Michael Shermer in his Nov. 2009 column in Scientific American comments that the likelihood of extraterrestrials with intelligence that are also humanoid is very small, perhaps only one other in the universe. Richard Dawkins disagrees, and reminds Shermer that Cambridge paleontologist S. C. Morris thinks that intelligent aliens would be “in effect bipedal primates” and Harvard University biologist Ed Wilson thinks that dinosaurs could have evolved into a humanoid type if the Alvarez impact never occurred. Shermer spars back, “If something like a smart, technological, bipedal humanoid has a certain level of inevitability because of how evolution unfolds, then it would have happened more than once here.” Shermer goes on to quote Ernst Mayr (2001), “Nothing demonstrates the improbablility of the origin of high intelligence better than the millions of phyletic lineages that failed to achieve it.” But then Dawkins responds that the universe is so big, and has so many inhabitable planets (presumably e.g. something like the Drake Equation), there must be more than a few humanoid civilizations.
I don’t know exactly where to begin. There is something wrong here on so many levels. The first is the hypothetical, “a certain level of inevitability because how evolution unfolds…” I’m not so sure that there is anything inevitable in evolution. I know that Shermer gave this as a hypothetical scenario, and probably doesn’t really accept this, but it sounds like Dawkins takes the bait. But we should know that any allegedly directional evolutionary trends “sooner or later either change direction or even reverse themselves (Mayr 2001).” If we see any trends at all it is just along the lines of what we know from evo-devo or Steven Jay Gould (2002), what we really see are the constraints of previous phylogenic histories that gave rise to developmental regulation in ontogeny.
But Morris and Wilson want to go beyond that and bemuse themselves that there may be some essential or directional push to become humanoid as if intelligence precludes that you must be bipedal, even a primate? I thought that orthogenesis was thoroughly refuted by the Modern Synthesis at least fifty years ago as again Mayr (2001) reminds us. There are no types. Being human is an endpoint in our lineage; that is all. There’s a certain logic to the assumption that an intelligent technologically advanced creature would have appendages that can manipulate objects with precision as in the grip afforded by the human opposable thumb. But bipedalism and opposability aren’t inevitable. I could understand why some might try work in some kind of directionality to evolution if one can’t divorce their biology from their theology, but let’s not even go there.
Extreme forms of this argument can be found in articles like that written by the planetary scientist Nancy Kiang in the April 2008 issue of Scientific American. Come let’s speculate on what plants would look like on other planets. Plants? We might as well ask what kind of vertebrate, what kind of tetrapod, what kind of reptile or amphibian, what kind of humanoid might we find? Did we forget of all the fits and starts and reverses that evolution took that resulted in terrestrial plants on Earth? Lynn Margulis reminds us (1998) that if it wasn’t for symbiotic fungi, there wouldn’t be any bloody plants. Plants aren’t inevitable, aren’t a type with an essence of autotrophism.
OK so it’s inevitable that there might be many intelligent life forms out there even if they’re not human? Even the skeptic Shermer concedes to this; Dawkins tries to remind us that the size of the universe might make it so. I just think that there is a certain simplicity here that seems to neglect how we really might begin to be able to calculate such a probability. We are constantly reminded that we really can’t do such a thing, but then we leap to the assumption that will be in favor of plenty of aliens to populate our potentially real Star Trek universe. There’s just an eerie resemblance to the simplistic argument for intelligent design…something like, “Creation is so complex, it must have been designed supernaturally.” If we oversimplify we end up with argument like that. Even if we can’t really calculate such a thing, I’d like to clarify at least what we need to consider before we even make such assumptions.
Even if you expect from a very similar basic imput of pre-biotic chemicals, life may have a certain probability, we are still at level of our prokaryotes. The expectation that complex multicellular life, then even human life, has some sort of probabilistic inevitability needs to be analyzed more than just superficially and in the context of the history of evolutionary theory.
Stereoscopic vision and opposable thumbs were probably adaptations to an arboreal life. Bipedalism may have been adaptation for locomotion for such a tree-loving creature after its environment started changing from forest to savannah. The human mind might be the result of emergent properties of the existing nervous system of hominids that were coapted to exploit an ever changing and complicated social landscape. Did we obtain these things through a directed process that inevitably resulted in a primate and a genus like Homo? Or do environments mold organisms into reoccurring, recognizable shapes that makes it likely that aliens would be recognizable to us as humanoid or even just multicellular? Just how inevitable are all these transitions?
The answer might lie in what I would call Critical Contingency Factors (CCFs) in the natural history of our planet. CCFs inform us how we think about the historical and contingent nature of biological evolution, and might allow us to begin to give more respect to what kind of evidence we would need to even begin to speculate about the frequency of life, even intelligent life on other planets.
Symbiotic Theory and Coevoltution. Perhaps the strongest argument for contigency in evolution is Symbiosis, two or more organisms that create an association sometimes intimately and permanently. Lynn Sagan (Margolis) in her historic paper (1969) on symbiosis demonstrated that the speculations of scientists as early as the late 19th century ( e.g. Schimper, 1883) had foundation, namely that some eukaryotic cellular organelles started out as prokaryotes, which associated with other prokaryotes and early eukaryotes to form the first unicellular animal and plant cells. For plants their precursors, algae, had to symbiotically associate with cyanobacteria (became chloroplasts) in order to photosynthesize. Before that critical event this organism already had another symbiont, the purple bacteria (became mitochondria), which made it possible to produce much energy in an atmosphere that was becoming ever more oxygenated (2 billion yrs. BP). Margolis developed her theory of symbiogenesis over the course of the next twenty years before the consensus caught up with her. By the time she published Symbiotic Planet (1998), she had the advantage of providing many, many examples beyond mitochondria and plastids of symbiotic associations that affected speciation events, changed lineages, creating even new genera. The point is that all of these events are completely unpredictable and contingent. Even the first eukaryotes are the product of both strict Darwinian evolution and symbiogenesis. The caveat here is that once the symbionts established a permanent relationship, subsequent change required natural selection per Darwin as Ernst Mayr reminded us in the forward to Margolis’ book. As for coevolution many organisms have evolved to keep in step with, to outcompete, and have arms races with other organisms that may not even be in the same domain, kingdom, phylum, etc. There’s no predicting what future associations organisms may have that affect their subsequent evolution.
Catastrophism. There have been as many as five previous global mass extinctions of life, not to mention the inevitably more numerous regional cataclysms (Gould 2002). It was just such events that remind us of the contingent nature of our natural history, and the affect that such events might inevitably have on the course of the evolution that ultimately created the diversity of life on Earth that man has been given the privilege to witness over the last 200,000 years. There is no way to predict what the future evolutionary path of any taxon could be after such events. New habitats open up if a major clade goes extinct. Unoccupied niches mean the potential of new adaptive zones. It is often stated that there never would have been the Age of Mammals if it hadn’t been for the extinction of the dinosaurs, which the consensus of the scientific community is
Emergence. It has often been remarked that the sort of intelligent cognition that humans have may be an emergent property of the evolution of our nervous system. All throughout the history of evolution at different turning points that beget perhaps a new genus, family, order, or class, biological systems that operate far out of equilibrium (as in Kaufmann 1993) make a biological-organizational leap to a new state of equilibrium upon which natural selection can shape further. Such events may mark the genesis of new adaptive radiations. Other examples might include:
1. Hypercyles of RNA that learn to replicate at first with first fidelity and then selectively evolve until some cycles approach the edge of thermodynamic equilibrium until a final snap into place, which marks a new metabolic efficiency that also just happens to inadvertently include a cellular membrane…the origin of life.
2. Genetic regulation in single cell eukarotes that at first aggregate as individuals, then reorganize the sort of phenotypic expression that allows for a division of labor amongst colonies…the birth of multicellularity…achieved perhaps by the push or pull of duplicated genes that maintain the old phenotypic expression as well as affect ontogeny in different ways as they mutate.
3. Genetic regulation in small, allopatric populations that as inbreeding continues, a loosening of the genotype occurs such that new pleiotropic regulatory networks are formed…typical speciation events at the micro/macroevolutionary divide.
All these scenarios start at the point of already having prokaryotic life, except for CCF Emergence #1. There are numerous more CCFs that precede the evolution of the first cell. I won’t go into those here but is interesting to mention that we can bring into the argument the same factors that creationists discuss, scenarios in which the conditions that allowed life to exist in our universe are very improbable. “Old Earth” creationist Hugh Ross in his book The Creator and the Cosmos (2001) discusses the many factors that reduce the possibility of ET life: large planets close enough, but not so far away that act as cosmic vacuum cleaners (e.g. Jupiter and Saturn in our solar system), and reduce the likelihood of asteroid and comet impacts on potentially habitable planets; our one moon allows a relatively reasonable wobble to our planet’s rotation; a habitable planet is one that is in the sweet spot in its solar system; the solar system has to be in a sweet spot in its galaxy; and many other points. Ironic to use a creationist argument, n'est-ce pas?
Many milestones in the evolution of life may have been the result of contigent, emergent properties that lead to new levels of biological organization. None of these turning points in our natural history were inevitable or predictable. Multicellular life may be very, very rare in the universe. We must be wary of any attempts to argue that there are inevitable progressions in evolution or some essence that is humanoid that MUST naturally occur on this or any other planet. I may have out-skeptified Michael Shermer.
Gould, S. J. (2002). The Stucture of Evolutionary Theory. Belknap Press, Cambridge.
Kaufmann, S.A. (1993). The Origins of Order. Oxford University Press, Oxford.
Kiang, N.Y. (Apr. 2008). “The color of plants on other worlds.” Sci. Am.
Margolis, L. (1998). Symbiotic Planet. Basic Books, New York.
Mayr, E. (2001). What evolution is. Basic Books, New York.
Ross, Hugh (2001). Creator and the cosmos. Navpress, Baltimore.
Schimper AFW (1883). "Über die Entwicklung der Chlorophyllkörner und Farbkörper". Bot. Zeitung 41: 105–14, 121–31, 137–46, 153–62.
Sagan (Margolis), L. (1967). "On the origin of mitosing cells". J Theor Bio. 14 (3): 255–274
Shermer, M. (Nov. 2009). Will ET look like us? Sci. Am. p. 36.