Intelligence: Darwin vs. Wallace

It's Charles Darwin's birthday today! He's 202. So in celebration I've written a post on the still ongoing controversy which the theory of evolution by natural selection caused and is causing, specifically with regards to the emergence of human intelligence.

Alfred Russel Wallace is widely seen as the co-discoverer of the theory of evolution by natural selection. While Darwin had been formulating his theory from as early as the late 1830s, he kept quite about it for more than twenty years while he amassed evidence to support it. In 1858 Alfred Russell Wallace, a naturalist of the same time, sent Darwin a letter outlining for him a theory of evolution which very closely mirrored Darwin’s own. The pair co-presented their theory to the Linnaean Society in 1858 but due to Darwin’s long time amassing evidence and refining his ideas, it was his book, On The Origin of Species, which was published in 1859 and set Darwin’s name firmly in the history books as the discoverer of natural selection.

While Wallace’s part in the discovery of natural selection is far from undocumented or unknown, it is largely for presenting ‘the same ideas’ as Darwin for which he is known and what is rarely discussed in the differences in their ideas. In this post I will briefly discuss a new(ish) paper by Steven Pinker on the evolution of human intelligence and some the differences between the thinking of Darwin and Wallace on the subject.

Darwin, unsurprisingly, asserted that the abstract nature of human intelligence can be fully explained by natural selection. In opposition to this Wallace claimed that it was of no use to ancestral humans and therefore could only be explained by intelligent design:

“Natural selection could only have endowed savage man with a brain a few degrees superior to that of an ape, whereas he actually possesses one very little inferior to that of a philosopher.”(Wallace, 1870:343)

Unsurprisingly most scientists these days do not agree with Wallace on either the point that the human brain could not be the result of natural selection or that as a result of this problem it must have been a product of design by a higher being. It would be both dismissive and dull to leave the discussion at that however, which is where Pinker comes in. Despite Wallace’s argument probably coming to the wrong conclusion he does bring up some very interesting questions which need answering, namely that of; “why do humans have the ability to pursue abstract intellectual feats such as science, mathematics, philosophy, and law, given that opportunities to exercise these talents did not exist in the foraging lifestyle in which humans evolved and would not have parlayed themselves into advantages in survival and reproduction even if they did?” (Pinker, 2010:8993)

Pinker addresses this question by outlining two hypotheses which can be combined to give quite a convincing explanation for the emergence of human intelligence:

1. The Cognitive Niche: Humans evolved to manipulate the environment through causal reasoning and social cooperation.

2. The psychological faculties that evolved to prosper in the cognitive niche can be coopted to abstract domains.

The Cognitive Niche

This hypothesis proposes that humans exploit a cognitive niche in the world’s ecosystems. This is achieved through a lifestyle which used reasoning about the causal structure of the world and cooperating with other individuals using language to take advantage of or change the environment to suit specific human needs.

Pinker identifies several “preadaptations” to this cognitive niche. These include our prehensile hands, meat eating and group living. After these are in place the ability to manipulate the environment can be selected for as this gives humans a greater advantage over other animals who have to slowly genetically evolve to deal with environmental challenges.

Pinker proposes that the adaptations which contributed to this cognitive niche coevolved with one another and with things such as greater parental investment, longer childhoods, longer lifespans and accumulation of knowledge and conventions in different cultures.

After this Cognitive niche evolved, over the course of history, humans accommodated themselves to the new skills and bodies of knowledge, provided by the cognitive niche, by a process of metaphorical abstraction, in which concepts that evolved to deal with concrete situations could naturally be extended to more abstract ones. Or, in terminology more familiar within evolutionary psychology, these abstract feats of reasoning are spandrels from more concrete predecessors.

Problems

Pinker’s theory is plausible but ultimately speculative and untestable. Pinker proposes using genetic testing within and across species to identify genes that were selected for whose effects are concentrated in intelligence, language, or sociality. This may not be as easy or plausible as it sounds for reasons very eloquently summarised over at "Why Evolution is True".

There has also been a viscious backlash to Pinker's paper recently from the intellegent design community, in the article by Michael Flannery the main qualm seems to be the speculative nature of Pinker's paper. Speculation within an evolutionary argument does not mean that it “isn't science” as it is labelled by Flannery. Pinker’s ideas are backed up with evidence, examples and based on known biological processes. Flannery’s proposed alternative explanation based on the fallacy ‘that specified complexity only arises from intelligent agency’ can only exist outside the realms of speculation BECAUSE it isn't science. The fact that a plausable theory exists which would explain how abstract reasoning may have emerged within humans should be enough to disprove the assertion that it could have only arisen through intellegent design.

So how can we test Pinker's theory?

"Why evolution is true" identifies only one convincing way to provide genetic evidence for Pinker being right and that is in showing that the human form of a gene, where the DNA differs between humans and chimpanzees, would improve the cognition of the chimpanzee. Due to this involving transgenic experiments, which are incredibly unethical, it is impossible to do this.

References

Darwin, C. (1959) On the origin of Species. London: John Murray.

Pinker S. (2010) The cognitive niche: Coevolution of intelligence, sociality, and language. Proceedings of the National Academy of Sciences USA, 107, 8893-8999

Wallace A. R. (1870) The limits of natural selection as applied to man. Contributions to the Theory of Natural Selection: A Series of Essays, ed Wallace AR (MacMillan, New York).

Pinker also discusses some of these ideas in chapter 3 of How the Mind Works and chapters 5 and 9 of The Stuff of Thought.

Sensible critique of Pinker at "Why Evolution is true":
http://whyevolutionistrue.wordpress.com/2010/05/31/did-humans-evolve-to-fill-a-cognitive-niche

Not-so-sensible critique of Pinker at "Evolution News":
http://www.evolutionnews.org/2011/01/a_one_hundred_year-old_challen043161.html

(Cross-posted at The 21st Floor)

  • Great Post! And thanks for reminding me of Darwin Day, I almost forgot! 🙂