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See Inside February 2009

Readers Respond on "The Search for Intelligence"

Letters to the editor on stories from Scientific American

Inscrutable Intelligence?
In “The Search for Intelligence,” Carl Zimmer relates the search for evidence of genetic influences on intelligence by Robert Plomin of the Institute of Psychiatry in London and others. Plomin’s many genetic studies have so far found only one plausible candidate for an “intelligence gene,” and it explains less than 1 percent of the variance on IQ tests. After such an extensive search, it seems likely that absence of evidence is evidence of absence.

Much of the argument for a genetic influence on intelligence is based on IQ test results, but there is very little theoretical backing for what these are testing. Philosophers such as Keith DeRose of Yale University maintain that whether you even know something depends on the context, including the stakes for getting it wrong. Many experimental results agree: Claude M. Steele of Stanford University, for instance, found that African-American students underperformed white students on a test that was framed as being diagnostic of intelligence but performed just as well as whites when this verbiage was absent.

There remains a widespread belief in genetic intelligence differences even though there is so little evidence, which makes the idea of intelligence genes resemble folk psychology. Such ideas do real damage in the classroom and beyond. For example, Carol S. Dweck of Stanford University has shown that students believing in preset intelligence perform worse than their counterparts who believe that intelligence is dynamic and results from hard work.

Given the shaky theoretical and experimental backing as well as the potential harm that belief in intelligence genes can do, I hope that researchers will start to question whether searching for a genetic basis of intelligence is worth the risk.
Luke Conlin
College Park, Md.

Bangs, Bounces and Black Holes
In “Follow the Bouncing Universe,” Martin Bojowald makes a compelling argument for the theory of loop quantum gravity, in which space is subdivided into “atoms” of volume and has a finite capacity to store matter and energy. This structure would prevent singularities, meaning that our universe may have existed before the big bang. Bojowald suggests that previous to the big bang, the universe may have undergone an implosion that was then reversed in a “big bounce,” followed by the big bang. He implies, I think, that this cycle may have been going on eternally. But in our current understanding, dark energy seems to promise that the universe will expand forever. Has our universe experienced its last bounce?
Robert Snyder
Andover, Mass.

According to loop quantum gravity theory, true singularities cannot exist. What, then, becomes of black holes?
Mark Saha
Santa Monica, Calif.

BOJOWALD REPLIES: In response to Snyder’s question, our big bang may have been the last (or only) bounce. Because we do not really know what dark energy is, however, its existence could well be the result of an intermediate form of matter, which might decay in the future. In this case, there can still be a future bounce. Observations in the not too distant future will tell us more about dark energy.

Regarding Saha’s letter, black holes are more difficult to analyze in quantum gravity than other regions of space because they are not as symmetric. (The gravitational force changes with the distance from the black hole, making the situation inhomogeneous.) Currently there are indications that the center of black holes is indeed nonsingular though still very dense. The usual horizons of black holes would form in loop quantum gravity, but light would be trapped only for a finite period. After the center bounces back, much like in cosmology, what has fallen into a black hole would be released.

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