Philip Yam is the News Editor of Scientific American Magazine. He recently posted an item on the magazine’s Web site about the death penalty. Some excerpts from the posting, entitled “Science versus the Death Penalty,” are below:

The U.S. remains the only developed Western nation to permit executions despite serious flaws in the system. No need for any pacificist proclivity or liberal leaning to see that—just look at the science.

First, there’s DNA evidence. Although it cannot prove guilt beyond all doubt—who can forget O.J. Simpson?—it can definitively prove innocence. The first DNA exoneration occurred in 1989, and since then many on death row have been set free because of it—the Death Penalty Information Center counts 122 exonerations since 1973. It showed that too many convictions resulted from sloppy or overzealous police work and prosecution, or incompetent defense attorneys. It helped convince then Republican governor George Ryan of Illinois in 2003 to declare the death penalty “arbitrary and capricious” and to commute the sentences of all 157 inmates on the state’s death row.

But DNA isn’t the only contribution from science to this issue. Thanks to psychology studies, we know that the human brain can, with rather disturbing ease, create false memories. (See, for instance, a news story on the topic in the December 2005 issue of Scientific American Mind, or the feature article “Creating False Memories,” by Eiizabeth Loftus in the September 1997 Scientific American.) We know that witness testimony can be unreliable, even when it comes from upstanding citizens and not just from co-defendants or jailhouse snitches who have been promised sweet deals. We know that some personality types are more likely to yield to the pressures to confess—and that these people do so just to please their interrogators or to avoid harsh treatment.

Most states are now recognizing the weaknesses of the death penalty. The number of capital sentences have dropped from a peak in the early to mid-1990s of a bit more than 300 per year to about 100 in 2005, according to data compiled in the December 17 issue of the Economist.

Science has shown that our death penalty system is deeply flawed. Now the U.S. public needs to see those flaws.

(Scientific American, Blog: Sciam Observations, posted Jan. 5, 2006 by Philip Yam). See also Innocence.