I have often wondered about whether key human adaptations (e.g., bipedalism, large brain size, opposable thumbs) represented universal traits for the development of high intelligence and technological complexity. In The Social Conquest of Earth (2012) by evolutionary biologist Edward O. Wilson, he posits that they are. Wilson argues that highly intelligent, technologically complex species have been so rare in the history of life because there are specific universal preadaptations required to produce the human condition. He contends that without these preadaptations, a species intelligent enough to "build a microscope, deduce the oxidative chemistry of photosynthesis, or photograph the moons of Saturn" is an impossibility (Wilson, 2012: 45). From Wilson himself:
"Overall, it now seems possible to draw a reasonably good explanation of why the human condition is a singularity, why the likes of it has occurred only once and took so long in coming. The reason is simply the extreme improbability of the preadaptations necessary for it to occur at all. Each of these evolutionary steps has been a full-blown adaptation in its own right. Each has required a particular sequence of one or more preadaptations that occurred previously. Homo sapiens is the only species of large mammal - thus large enough to evolve a human-sized brain - to have made every one of the required lucky turns in the evolutionary maze." (Wilson, 2012: 45)
So what are these "lucky turns"? And are they as universal as Wilson supposes? First I think it is appropriate to explain what is meant be an "evolutionary maze." An evolutionary maze is a metaphor to understand the probability of an organism acquiring a certain trait (i.e. large size, flight, echolocation, intelligence, etc.). By using this metaphor we can say with certainty that descendants of contemporary pigs could become aquatic, but will never be able to fly. This is because their ancestors acquired adaptations that "closed the door" to flight as a future adaptation through the evolutionary maze. In essence, Wilson uses this metaphor to illustrate how many, and what type, of preadaptations it took for evolution to produce a highly intelligent, technologically complex species. So that brings us back to "lucky turns". What were they for us? And can we deduce that these preadaptations represent a universal process for biological evolution? Is the human condition a singularity? According to Wilson there were four major turns, and these turns can be seen as prerequisites for biological evolution to produce another species with our abilities:
The first of Wilson's lucky turns is an adaptation to a terrestrial environment. This is the first key preadaptation because Wilson argues that technological evolution past simple stone tools requires fire. This means that in the evolutionary maze aquatic species could develop technology, but could never develop technologies with evolutionary trajectories of their own. Therefore, no descendant of the octopus or dolphin could deduce oxidative chemistry of photosynthesis, or photograph the moons of Saturn, without first adapting to land.
2. Large body size
Wilson's next preadaptation is large body size. The reason for this adaptation is fairly self-explanatory: in order for a species to develop human-level intelligence, they must have a body that can support the evolution of a human-sized brain. Wilson draws on his experience studying the highly complex societies of ants, bees, and termites to support the inclusion of this preadaptation: "[body size is the] one reason why leafcutter ants, although the most complex of any species other than humans, and even though they practice agriculture in air-conditioned cities of their own instinctual devising, have made no significant further advance during the twenty million years of their existence." (Wilson, 2012: 46). In contrast, we acquired this adaptation gradually over time within the order primates.
3. Grasping hands
The third preadaptation is grasping hands. For Wilson, a species that has not acquired this ability will never be able to manipulate the environment in the way necessary to produce complex technologies. Of course, this is a preadaptation that our lineage acquired within the order primates. Grasping hands distinguishes primates from all other mammals.
4. Meat/Control of Fire
The fourth preadaptations are the consumption of meat and control of fire. Meat is a necessary adaptation for Wilson because it yields higher energy per gram eaten, and because of the cooperation between individuals required to acquire meat. In our lineage, meat was first consumed regularly within the genus Homo. Before this the australopithecines subsisted off of vegetation, although they were potential scavengers as well. Regular consumption of meat was followed shortly by the control of fire. For humans, control of fire allowed us to catch larger game, and created a central common cooking space, which facilitated the development of an even more complex social environment dependent on altruistic sharing of resources.
The Evolutionary Maze
The metaphor of the evolutionary maze is a useful one. It can help us conceptualize biological evolution. However, Wilson depicts the human journey through the maze to be the only possible way for biological evolution to produce both high intelligence and technologically complex species. Of course, I agree that the maze towards these evolutionary developments is narrower than the maze towards less complex adaptations. I also agree that a great number of preadaptations are necessary for a species to achieve high intelligence and technological complexity. However, the human condition may not be a singularity. Unfortunately, we know of only one species that has developed high intelligence and technology with an evolutionary trajectory of its own. Therefore, our sample size is too small to be definitively sure that our path through the maze was the only one.
As a consequence, I believe questions about the universality of the human condition must be relegated to a grey borderland between philosophy and empirical science. Are there universal preadaptations? I think it is possible, but we can't scientifically determine that yet. Take for example Wilson's first preadaptation: adaptation to land. Is it impossible for a lineage adapted to an aquatic setting to develop high intelligence and technological complexity? I am just not sure how we can scientifically rule that out. Just because it hasn't happened on Earth, doesn't mean that it can't happen in the future, or on some other planet similar to our own.
As Wilson point out in the book, alien scientists studying our planet three million years ago would likely think nothing special of the australopithecines. However, they were part of the maze that ended up producing us. Could our species be making a similar mistake as Wilson's hypothetical alien scientists if we conclude that the evolutionary maze to high intelligence and technological complexity is shut to the descendants of octopuses and dolphins? Furthermore, we can't conclude that consumption of meat and control of fire are necessary preadaptations, even though they were for us. Although meat yields higher energy per gram eaten when compared to vegetation on Earth, it may not be the case on other planets. I would argue the same with the preadaptation for control of fire. It was important for our lineage, but could technology develop without control of it in an aquatic setting? We don't have the data to rule it out.
On the other hand, I believe the preadaptations Wilson explored do give us important insight. For example, I would think it to be highly unlikely for a species with a small body size to develop human-level intelligence. As he mentioned, the lack of advance among the social insects is likely attributable to this variable. Also, I am in general agreement with Wilson that a species like us would require some type of grasping preadaptation. Of course, grasping hands could be supplemented for the evolution of some other type of appendage (e.g., fin, tentacle, etc.) that could be used to manipulate the external environment.
This means all intelligent science fiction aliens should be equipped with some type of grasping appendage, in order to be scientifically appropriate. Jokes aside, this type of question is worth exploring. However, I think we should be cautious and hesitant to make any broad conclusions. A scientific consensus will not likely be reached until we have more data, and that requires understanding life off of our island of life: Earth.
Wilson, E.O. 2012. The Social Conquest of Earth. New York: W.W. Norton.