Lost amid all the recent discussions of intelligent design -- including Louisiana Governor Bobby Jindal's decision this past Friday to sign a bill that allows teachers in his state to "supplement" classes on evolution with talk of creationism -- is one simple basic fact. The human species isn't intelligently designed.
When you get right down to it, from an engineering perspective, the design of the human mind (and for the matter the human body) is a bit of mess.
Take, for instance, human memory, and the trouble we often have in remembering even the most basic facts -- where did we put our keys? Where did we park our car? Because our brains so often blur our memories together. Human eyewitness testimony is often no match for even a low-rent survelllance camera, and memory can fail even in life-or-death circumstances. (6% of all skydiving fatalities, for instance, are from divers that forgot to pull their ripcords),
Our troubles with memory in turn lead to an unending litany of problems that the psychologist Timothy Wilson collectively refers to as "mental contamination", in which irrelevant information frequently, ranging from the physical attractiveness of political candidates to random numbers on a roulette wheel, subconsciously cloud human judgments. If an ugly child throws an ice-filled snowballs, for instance, we judge that child to be delinquent, but when an especially attractive child does the same thing, we excuse him, saying he's just "having a bad day." A study published earlier this month showed that people's moral judgments are more severe when made in a disgusting, soiled pizza-box filled office than when in an office that is neat as a pin; another, which appeared just last week in the Proceedings of the National Academy of Sciences, shows that voters are more likely to favor school policies if the balloting takes place in a school than if it takes place in an apartment building. We may aspire, as Aristotle thought, to be "the rational animal", but in reality the flotsam and jetsam of barely conscious memory frequently intercedes.
At this point, 30 years after the Nobel Laureate Daniel Kahneman and his late collaborator Amos Tversky started documenting a rash of fallacies in human reasoning, the idea that the human mind would be "perfect in His image" is as outdated (and narcissistic) as the idea that the solar system would revolve around the planet earth.
Imperfections riddle the body as well; the human spine supports 70% of our body weight with a single column, where four might have distributed the load better (greatly reducing the incidence of debilitating back pain), and the human retina is effectively installed backwards, with its array of outgoing neural fibers coming out of the front rather than the back, saddling us with an entirely needless blindspot.
The only theory that can really make sense of these needless imperfections is Darwin's theory of natural selection, which holds that humans (and all other life forms) evolve through a blind process known as descent-with-modification, in which new life forms represent random modifications of earlier life forms -- with no central overseer to guide the process. Such a random process can, over time, lead populations of creatures to become more adapted to their environment, but it is also vulnerable to getting stuck, in the sort of good-enough-but-not-perfect solutions that mathematicians call local maxima.
A local maximum is like a moderately high peak in a rugged mountain range that is filled with other peaks, some of which are considerably higher; a peak at the top of the treeline, when there are plenty of snow-capped peaks that loom considerably higher. The process of natural selection is vulnerable to such limits for two reasons: it is blind, and it generally takes only small steps; as such, it can easily get stuck on low-lying peaks that are impressive but well short of the highest possible mountaintop, designs that are "good enough for government work" but far from perfect.
Darwin gives a natural explanation that indicates poorly-designed features should be common in biology. The theory of intelligent design, in contrast, has a serious problem explaining such phenomena: an intelligent designer that could perceive the whole landscape could just pick us up and move us to higher ground. That this has never happened is clear testament both to the wisdom of the theory of natural selection and the implausibility of intelligent design.
The problem with the Lousiana law is not just that it seeks to mix church and state, a situation that the Constitution's framers rightly sought to avoid, but that it is predicated on the assumption that creationists have a reasonable theory with which to counter evolution with - where in truth they simply don't.
-- Gary Marcus, Professor of Psychology at New York University, is the author of Kluge: The Haphazard Construction of the Human Mind.