Alfred Russell Wallace, whose famous letter had alerted Charles Darwin in 1858 that he was in danger of being scooped on the principle of natural selection, broke with the principle just where it applied to human intelligence. Wallace accepted that humans developed from the apes, but he had little respect for the mental abilities of “savages”, and could not see how the higher mental properties shown by civilized people could have evolved gradually by natural selection in the wild (Wallace, 1889). Wallace strongly believed in the power of natural selection, but for this one human character he was an exceptionalist. Darwin wrote The Descent of Man (1871), to explore the ways in which humans evolved, as he thought, within the same genus as the great apes of Africa, and how, building on the limited intelligence of animals, step by step human populations competed by developing new “arts”.
The Wallace Paradox has attracted philosophers. In a review (2001) of a book by Stephen Pinker, Bringsjord, for example, used the following argument:
1. If people evolved, then for every power possessed by our foraging ancestors, there exists a problem faced by them or their predecessors such that the power deals with the problem
2. It’s not the case that for every power possessed by our foraging ancestors, there exists a problem faced by them or their predecessors such that the power deals with the problem
3. Therefore people didn’t evolve (from 1 and 2).
The logic here is not contested. But is the conclusion correct? The answer is No. One or both of the premises must be faulty. I leave aside premise 2 because I think it may be correct. Based on what we know today about the mechanism of evolution, however, the first premise is incorrect. There are latent powers, produced incidentally in the evolution of others, that are later taken advantage of in the process of evolution. Gould and Lewontin (1979) called these spandrels. Darwin was the first to propose their existence as precursors to adaptations. Another word for them is preadaptations, but this is not a good term because it lends itself to misinterpretation. A good example of a spandrel that Gould (2002) cited is the adaptation of a whole variety of enzymes, such as lactate dehydrogenase, to act as crystallins to give both stiffness and transparency to the lens of the eye. Another is the umbilical brooding chamber in certain snails, which in ancestral species was not used for anything. Still another is the bird feather, which evolved among dinosaurs that could not fly and most likely was initially adapted for heat regulation. Its suitability for assisting flight is a coincidence. After all, feathers cover the entire body of the bird, not just the wings and tail. Gould wrote that spandrels may lie at the origin of a very large proportion of all adaptive traits. But even if there is only one good example in all of biology, premise 1 is formally incorrect, because it does not adequately describe the mechanism of evolution. Nor does it hold water to object that we do not know the details of how brain evolution actually happened in humans. Of course we do not know them. That is the difference between science and revealed religion – there is something left to discover, always. It also does not do to claim, as Bringsjord does, that an appeal to exaptationism represents a form of special pleading. The idea of exaptations was not developed to address the Wallace paradox, but to explain a large array of facts about the biology of all sorts of organisms. So the Bringsjord argument does not prove that people didn’t evolve, whatever “people” means. Indeed it seems unlikely on the face of it that this type of approach – attempting to summarize evolutionary theory into a single premise – could lead to a reliable result. Of course it remains possible that people did not evolve, but it really is simpler to assume that they did than that they did not. This marks the place where philosophy leaves off and science begins.
The remarkable mental powers of humans may well be examples of extreme traits produced by many small steps. No doubt many of these took place in response to selection in favor of them (conditioned by both biological and cultural factors) that outweighed the costs in our ancestors. Many of them however could represent spandrels, i.e. traits that do one thing in one environment but play a very different role in another. The unique nature of this trend in humans is attributable, on this view, to the fact that humans developed a far more elaborate culture than any other animal. In other words human intelligence, as commonly understood, evolved in large part in response to a uniquely human character, i.e., a complex culture. It is easy to see that this would have fed on itself in an exponential way. In that sense it is not unlike other runaway traits, such as have occurred during sexual selection among some animals, and which in some cases seem to have no other correlate except that they promote selective mating – the peacock’s gaudy tail is the most familiar example.
Another mechanism producing extreme traits is co-evolution. Consider the famous example of the orchid, Angraecum sesquipedale in Madagascar, discovered by Darwin during the voyage of the Beagle. This plant has an extremely long spur, 20 to 25 cm from its tip to the tip of the flower’s lip. The pollen is found at the bottom of this long tube. Darwin knew that other orchids were pollinated by moths, and he predicted that a moth would be found with a proboscis long enough to get to the bottom of this spur. Over 50 years later, this moth (Xanthopan morganii praedicta) was found and has been observed since many times pollinating this very species of flower.
Xanthophan morganii, the moth predicted by Darwin. The proboscis is 11 inches long, several times the length of the rest of the animal’s body.
It is easy to build an exceptionalist argument for the intervention of special forces in the evolution of Xanthophan. For surely it has an amazingly extreme character, several times the length of the rest of its body, in this long proboscis. Why would not this moth in effect give up and feed on another orchid? Surely only special forces could be at work here, producing this extraordinary anatomy? But I suspect few will feel the force of this “argument” because after all it has to do with insects and flowering plants and not with people. Others with more justice might feel that it would not have happened if Xanthophan were not constrained to feed on only this one species of orchid. Nobody has a vested interest in proving this insect special. The scenario of co-evolution seems perfectly acceptable: As the spurs got deeper and deeper with each succeeding generation (keeping out the wrong pollinators), the probosci got longer and longer (continuing to get the nectar). What is remarkable is not the co-evolutionary process per se, which is commonplace, but the sheer magnitude of the result. Off the top, one would not have thought it possible, but there it is. Here is a link to a video showing both the orchid and the moth.
The point is that step by step processes can produce remarkable adaptations, far beyond what intuition would lead us to expect.
Just Who is the Savage?
A few generations ago, many civilized populations in the world were living as hunter-gatherers. On an evolutionary time scale they have adapted to civilized life very rapidly. It seems likely that only cultural forces could have acted so fast – the innate capacity of humans, whether they are civilized or not, is the same all over the earth and has likely been so for tens of thousands of years (think of the cave paintings at Lascaux (15,000 years old) or the hand paintings of aborigines who arrived in Australia 40,000 to 60,000 years ago). This insight is something we have acquired since the time of Wallace (1889), who wrote disparagingly about the mental abilities of “savages.” So how might one resolve the Wallace paradox? Are people smarter than they had to be to live as hunter-gatherers? Personally, I do not know how smart one has to be to survive as a hunter-gatherer. I suspect that most civilized people would be goners if forced to live that way, without prior training. But let us suppose it is true that people are smarter than required by that style of life. How did they get that way? Do we really have to suppose, like Wallace, that a purposeful force was involved?
The answer is of course not. Wallace, a brilliant man, was nonetheless a creature of his time, like Darwin. He did not realize that the hunter gatherer peoples are not mentally inferior to civilized peoples. We know for example that many Australian aborigines have entered into the cultural life of civilized Australia. Culture and education are responsible for the fact that people go around doing algebra (well, some of us anyway). The hunter-gatherer brain is a spandrel, whose potential was unlocked by the remarkable acceleration of human culture. But physically and genetically, it is the same in all human populations and likely has remained essentially unchanged for thousands of years and possibly over the known lifetime of Homo sapiens. It is entirely possible that it evolved in response to the constantly expanding and differentiating culture of the human species, always placing a premium on mental agility and creativity.
The monolith in 2001: A Space Odyssey. In the story, apes touch this (accompanied by the Music of G. Ligeti and J. Straus), and wake up smart the next day.
The evidence for human evolution from a common ancestor with the African great apes is overwhelming, both at the morphological level and at the level of DNA sequence analysis. The fossil record and molecular evidence leave little doubt that the mechanisms involved are essentially the same as those that governed the evolution of all the other organisms on earth. All of our intellectual achievements are built on the biological and cultural foundation of hunter-gatherers of our species originating in Africa as long as 200,000 years ago, who in turn can be traced to a common ancestor with the African great apes. There is no evidence that at any point some external, purposeful, Clarke/Kubrick event (as in the film 2001: A Space Odyssey) triggered a mental revolution in Homo sapiens. The Wallace Paradox rested on a foundation of prejudice based on cultural differences.
Bringsjord, S Are we computers? A critical review of Steven Pinker’s How the Mind Works. Philosophical Psychology 14, p. 227, 2001
2001 – A Space Odyssey, a film by Stanley Kubrick. 1968
Darwin, C. The Descent of Man, and Selection in Relation to Sex. Murray, London, 1871
Gould, SJ The Structure of Evolutionary Theory. Harvard University Press, Cambridge MA 2002.
Gould, SJ and Lewontin, RC (1979) The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme Proceedings Of The Royal Society of London, Series B, Vol. 205, No. 1161 (1979), Pp. 581-598.
Wallace, AR (1889) Darwinism.