Writing in Trends in Genetics, Gerald Crabtree of Stanford University has proposed that humans may actually be getting stupider not smarter (“Our Fragile Intellect“). What happened to the Darwnist’s mantra of progress? Are we not the product of many generations of natural selection? At first glance Crabtree’s theory runs contrary to the typical evolutionary paradigm, but he is actually reviving an argument that Darwin made a century ago.
Give him this much credit: Crabtree has a refreshingly different take on the progress of humanity. He rejects the kind of temporal favoritism that is implied in the works of many Darwinian evolutionists. Rather than assuming that hunter-gathers are de facto less intelligent than we are today (because we have evolved and we have science), he points to evidence for language and abstract thought as counterarguments to the smug assumption that our age is the smartest age. There is no reason to believe that early humans were less mentally adept than we are. True, their brains may have worked differently (they didn’t have texting, driving, television or the Internet), but as Crabtree points out, hunting requires a certain intellectual rigor that we, who buy our meat at the supermarket, tend to forget.
On the other hand, Crabtree seems to make assumptions of his own about what intelligence is. He does not give a specific definition, although he touches on its having something to do with the ability for abstract thought, but then switches his focus to intelligence based on functional ability (e.g., hunting, playing chess, and doing dishes). Hunter-gatherers were really good at hunting, and if an individual was particularly bad at it, then he would likely not survive to pass his genes on. In other words, the ones that were good at hunting were selected, and since Crabtree takes the view that intelligence is based on functional capability, he believes the smarter individuals were selected — that is, the better hunters.
Crabtree says that we started losing our intellectual abilities because selection pressures weakened:

When might we have begun to loss these abilities? Most likely we started our slide with the invention of agriculture, which enabled high density living in cities. Selective pressure was then turned to resistance to diseases that naturally grow out of high-density, urban living. A principle of genetics is that when one selects highly for one trait (such as resistance to infectious disease) other traits are inadvertently selected against. It is also quite likely that the need for intelligence was reduced as we began to live in supportive, high-density cities that made up for lapses of judgment or failure of comprehension. Community life would, I believe, tend to reduce the selective pressure placed on every individual, every day of their life; indeed that’s why I prefer to live in such a society.

Crabtree’s assumptions are most apparent in the examples he gives of how easily a single mutation can affect our mental abilities. He uses the examples of Down’s syndrome and autism. In this, combined with his views on genetic reductionism, he comes a little too close for comfort to some of Darwin’s arguments in Descent of Man and certain eugenics arguments.
The idea was that our society was too permissive in allowing “weaker” individuals to live, when, if we did not have things like medical intervention and social welfare, they would have died out before they were able to reproduce. Granted that Crabtree seems to think everyone is “getting stupider”; however in order to conduct any kind of test of his hypothesis, you would have to look for traits that have been deemed “dumb” traits. While not stating it explicitly, he indeed has in mind a particular definition of intelligence.
On two other points Crabtree slightly deviates from the typical evolutionary paradigm: First, he recognizes that mutations are typically harmful rather than helpful, and it is on this basis that he builds his thesis that we are getting dumber rather than smarter. We have all had at least two intellectually deleterious mutations, and therefore must be dumber than our ancestors:

Another way to state the same information is that every twenty to fifty generations we should sustain a deleterious mutation. Within 3000 years or about 120 generations we have all very likely sustained two or more mutations harmful to our intellectual or emotional stability.

Secondly, genetic reductionism holds that our traits, whether physical or behavior, can be traced to our genetic code. Taking an extreme position on genetic reductionism is called genetic determinism, which assumes that people are incapable of acting outside of their genetic make-up, in essence lacking freewill. Crabtree reminds us in his paper that the one-gene-one trait idea is a fallacy. While there may be certain discrete genetic defects that produce a particular disease, scientists have conceded that most of our traits involve multiple genes. He shows that there are hundred, if not thousands of genes that code for intelligence, at least according to the way Crabtree defines it.
Crabtree is still a reductionist in the sense that he assumes intelligence is predominantly genetic. He thinks our genetic markers for intelligence are remarkably fragile, and mutations are remarkably robust, and, therefore, we are still a product of our genes. But he does not assume that there is a single gene for one trait. He takes a more holistic and complex view of the genome.
Yet much of this paper is a just-so story, and several non-ID friendly critics have pointed this out (see here, here, and here). His thesis is not verifiable (How do we know we are getting dumber and what does intelligence even mean?), and his explanation of how we evolved the trait and then lost it has the flavor of a neat narrative rather than observational deduction or even extrapolation.
His paper brought to mind an article published in The Atlantic four years ago, later expanded into a book, “Does Google Make Us Stupid?” The author, Nicholas Carr, proposed that rather than community, cities and agriculture, perhaps it’s relying on the Internet that is making us stupid. Hyper-stimulation has certainly decreased our attention spans, and some would argue that being able to pay attention is the most indispensible prerequisite of genius. Crabtree’s point is that natural selection, in a technological, communal society, selects for things other than inherent intelligence, so mutations that degrade our intelligence (whatever that may be) are “permitted” to perpetuate.
Or, perhaps we still have strong selection pressures, but they operate in a different way. As one of his critics suggests, being a Wall Street CEO puts you in a high-pressure, competitive environment all its own, which one could argue has certain reproductive selective pressures. Or, perhaps as suggested by Nicholas Carr, our brains become re-wired based on our environment. In that case, environment rather than genetics is the key player in determining intelligence. If true, that would put the kibosh on Crabtree’s theory.
Image credit: Dru!/Flickr.