In “The World without Free Will,” Azim F. Shariff and Kathleen D. Vohs assert that a survey revealed that “the more people doubt free will, the less they favor ‘retributive’ punishment” and indicate that the notion of free will is necessary to social order. What constitutes human freedom is a complex matter, fraught with ambiguities that have been debated for millennia. The authors don't clarify the survey's questions. For instance, what if it had asked respondents to rate the relative influence of several factors, such as physical laws, biological impulses, life experiences, the cultural environment, rational deliberation or a sense of self-determination? Wouldn't that have elicited a more nuanced response?

Richard M. Rubin
Adjunct lecturer in philosophy Washington University in St. Louis

Shariff and Vohs ask the question “What will our society do if it finds itself without the concept of free will?” But they do little to clarify the issue. They show, at best, that there is a temporary disturbance in the moral compass of people freshly exposed to the idea that free will does not exist. Many things have the same temporary effect, including emotional states such as love or hate and war or abuse. The important question is whether a prolonged exposure to a different view of free will changes us. To answer that, there are plenty of historical and anthropological data to prioritize over those they discuss.

Raymond Duchesne
Round Hill, Va.

In “The Ponzi Economy,” Kaushik Basu does a great disservice to those of us involved in the day-to-day operations of the economy by implying that many of the activities we undertake are no different from a scam. His article easily fits with preconceived notions that actively engaging in commerce is somehow demeaning and morally bankrupt. (Witness that the only emotion allowed private-sector participants is greed.)

Thomas A. Fink
North Caldwell, N.J.

Despite the title of Basu's article, he doesn't draw what seems to me the inevitable conclusion that the dominant global economic paradigm (neoliberal capitalism) is itself a mega-Ponzi scheme. It is predicated on infinite growth, there is no graceful way to a soft landing, the system collapses when growth is no longer possible, and we can't predict a well-defined point at which the crash occurs.

John O'Hara
Mount Waverley, Australia

In addition to the excellent points Ann M. Graybiel and Kyle S. Smith make about the difficulties people face as they try to change habits in “Good Habits, Bad Habits,” there are the social barriers such individuals face from the social groups they are a part of. Working in a part of health care that deals with this constantly, I have had some patients who had to change friends because they were no longer accepted because of their healthier behavior and others chastised by their boss for not participating in every pizza party or early-morning doughnut meeting. Most people with bad habits are just well adapted to a social environment of bad habits.

Mike Taylor
via e-mail

In his article describing biosensors that can quickly identify viral, bacterial or fungal origins of disease [“Germ Catcher”], David J. Ecker asserts that 43 adenine, 28 guanine, 19 cytosine and 35 thymine nucleotide subunits constitute a unique solution for a DNA strand weighing 38,765.05 daltons. I tried to duplicate the result and got about 10 possible solutions. Can you shed some further light on this very interesting technique?

David Mawdsley
Danbury, Conn.

Would it be possible to use the technological machinery Ecker describes to determine the differences in the flora of the digestive tract between people who are of a healthy weight and those who suffer from morbid obesity? If this is a possibility, then a probiotic could be specifically developed for particular individuals' needs, improving their digestive flora to make weight loss an easier process.

Ron Rega
Marietta, Ga.

ECKER REPLIES: Mawdsley is correct. Referring to 38,765.05 daltons as corresponding uniquely to a DNA strand containing the subunits 43 adenine, 28 guanine, 19 cytosine and 35 thymine was a simplification for illustrative purposes. With additional decimal points in the measurement, however, the solution does become unique. But this ignores the fact that there is a 10-parts-per-million (ppm) error in the measurement, which would actually enable nearly 1,000 possible base compositions as correct solutions!

But because our system separates the double-stranded DNA and independently measures each of the single strands and because we know that the A count in one strand must equal the T count in its double-helical partner (same for G and C), at a measurement deviation tolerance of 10 ppm, there is only one solution that fits for both strands. Constraining the problem by considering both strands in conjunction with Watson-Crick rules is part of the algorithm used by the technology.

In reply to Rega: Indeed, the system could, in theory, be used to characterize intestinal flora and might be used to provide a picture of the “enterotype,” or microbiota, of individuals and then to measure perturbations that result from prebiotic or probiotic therapy.

The question of how newborns acquire their flora at birth, brought up in “Gut Reactions,” by Claudia Wallis [The Science of Health], remains fascinating and unanswered. As a midwife, I do not rupture the sealed fetal sac. It usually spontaneously ruptures, but in 5 percent of my births, the baby emerges in the intact sac, never directly exposed to the mother's vaginal or intestinal flora. Breast-feeding is a possible route for the immediate colonization of the intestines after birth. If so, how do intestinal bacteria get into the milk?

Judy Slome Cohain
Certified nurse midwife Alon Shvut, Israel

WALLIS REPLIES: To begin with, the uterine environment is not the pristine place it was once thought to be; microbes are present there and in the placenta. Second, during birth it is likely there would be some contact with the mother's microbes even when the sac is unbroken. Third, according to Maria Gloria Dominguez-Bello of the New York University School of Medicine, the mother's nipples and milk ducts very likely harbor bacteria that thrive in milk and that these then colonize the infant gut.

“Full Disclosure,” by the Editors [Science Agenda], gives the generic name of Vioxx as celecoxib. It is rofecoxib.

“A Milestone on the Long and Winding Road to Fusion,” by David Biello, states that lasers at Lawrence Livermore National Laboratory used to produce fusion require about 500 trillion joules. The figure should be at least 190 million joules.

“Summon the Rain,” by Dan Baum, incorrectly refers to the volume of a small cloud as topping 750 cubic kilometers. A typical cloud is one cubic kilometer.