The title of Helen Branswell’s “Flu Factories” is the type of sensationalism that has to be overcome for influenza surveillance to be effective and was in stark contrast to the balanced report that followed. Also, since the article was written, there has been significant progress on the implementation of a national influenza surveillance program in swine. In the program, which started in May 2009, pork producers and their veterinarians submit tissues to one of 37 veterinary diagnostic laboratories nationwide. Genetic sequences of isolated flu virus are entered into a database, then published and made available for review by experts and the public. Should there be a sequence of interest, the public or animal health surveillance systems in the state of origin can be alerted. To educate pork producers about this surveillance plan, direct mailings and other communications have been sent to more than 67,000 producers and to all state animal health officials and public health veterinarians. The results have been remarkable. During November 2010 alone, 490 samples were tested, compared with a previous monthly average of fewer than 200. U.S. pork producers and their families live with these animals, and they take the role they have in protecting public health very seriously.
Paul Sundberg
Vice President, Science and Technology
National Pork Board

Tim Folger’s “Contact: The Day After” cites the well-known equation by Frank Drake, which argues for a galaxy full of sentient life. Yet no artificial signal has been detected, and we wonder why. The Drake equation includes a term L, which represents the life span of an alien civilization, but the implicit assumption is that such a civilization would emit signals we could both detect and recognize during its entire life span following its invention of radio. But here on Earth we can already see the failure of that assumption in two ways.

First, after less than 100 years of beacon­like transmissions, the day of the 50-kilowatt broadcast antenna is drawing to a close, as communications technology advances to coaxial, fiber-optic, and short-range, low-power systems. Even geosynchronous satellite communication is aimed down, parsimoniously covering only a portion of Earth’s surface.

Second, every broadcast medium is moving to a digital format, and digital means data compression. Data compression removes redundancies—that is, any recognizable pattern in the signal—and replaces them with a compact digital code. Perfectly compressed digital data are thus indistinguishable from random noise.

These changes have overtaken human communications technology within only a few decades of Guglielmo Marconi’s first work. I can only conclude that we could be sitting in the midst of a “Galaxy-Wide Web” of alien chatter, which to us, without the algorithms to decode it, appears like noise. Perhaps Drake’s L value should be kept to under 50 years, and perhaps SETI could try to think of ways to detect digital signals embodying advanced compression—signals that look just like noise.
Grant Hallman
Huntsville, Ontario

The article “Radioactive Smoke,” by Brianna Rego, shed more light on cigarette manufacturers and their not so ethical practices. If tobacco growers are using fertilizer on their plants, it obviously works, even though it is made from uranium-rich phosphate rock and results in polonium 210—a decay product of uranium—being inhaled with cigarette smoke. But as a nonsmoker, I wonder just where else this polonium may lie. Are food growers using the same type of fertilizer? What about cotton growers?
Rachel Allgood
Savannah, Ga.

THE EDITORS REPLY: Polonium 210 emits alpha radiation, which loses energy rapidly in the air and is blocked by clothing or by human skin. Thus, it is harmless when outside the body. The isotope does pose some cancer risk when ingested, but according to Argonne National Laboratory, the risks from inhalation—as through cigarette smoke—are about six times higher than for dietary ingestion.

Although the discovery of internal fertilization in 375-million-year-old fossils is as important as John A. Long makes it out to be in “Dawn of the Deed,” his article made the leap from placoderms to tetrapods without mention of lobe-finned fish. The fossil fish Tiktaalik, discovered in 2006, dates back to the same period, and its skeleton bears many more similarities to tetrapods than to the placoderms described in Long’s article—including homologous arm bones and shoulder, neck and ear features. If, as his article suggests, claspers are the progenitors of tetrapod limbs, then where do nearly amphibious lobe-finned fish such as Tiktaalik, of the same age as his placoderms, fit in this phylogeny?
Robert Wilson
Salt Lake City

LONG REPLIES: Tiktaalik is as close as a fish can get to being a tetrapod; the only things it lacks are fingers and toes. Unfortunately, the available fossils of tetrapodlike fish such as Tiktaalik and early tetrapods carry no evidence of how they reproduced. The closest living relatives of these transitional creatures are the lobe-finned fishes, including the lungfishes, which spawn in water, and the coelacanth, which has internal fertilization despite lacking claspers. Internal fertilization by copulation has evolved independently many times during vertebrate evolution, with many lineages retaining simple spawning. But whether these modern-day species spawn or copulate, the equipment they use to get the job done derives from the same embryonic tissue under the direction of the same so-called hox genes that formed claspers in placoderms.

In “Don’t Worry about Who’s Watching” [TechnoFiles], David Pogue assures us that there is little to fear about the potentially vast database that an interested party might assemble about any or all of us in a matter of days. Governments are not always as benign as the ones that some of us now enjoy. History offers plenty of examples where a regime bent on total domination found it worthwhile to assemble dossiers on tens or hundreds of thousands of innocent individuals. The time, difficulty and expense required to gath­er information on masses of citizens have decreased exponentially, and the motivation to use such information for evil purposes can be aroused from dormancy just as easily.
David A. Burack
Brooklyn, N.Y.

Many readers wrote that they were confounded by John Allen Paulos’s description of the Monty Hall Problem in “Animal Instincts” [Advances]. A full description of the paradox would take up too much space here, but you can read more on this topic at www.ScientificAmerican.com/may2011/monty-hall.