In describing their conclusions that DNA segments, or jumping genes, that can copy themselves into different parts of the genome may be the cause of the uniqueness of individual brains in “What Makes Each Brain Unique,” Fred H. Gage and Alysson R. Muotri misrepresent the degree of similarity expected between the brains of identical twins. Their work does reveal an intriguing source of genetic variation between such brains, the significance of which remains to be elucidated.

Yet the authors gloss over the fact that all brains, genetically identical or otherwise, are almost certainly quite distinct as a result of inherent variation in neural stem cell divisions, cell migration events and neural circuit formation. Such variation is created by the unique, probably often random, cellular and experience-dependent interactions that occur during the development of any given brain.

Nicholas Gaiano
Johns Hopkins University
School of Medicine

Having worked with start-ups and early-stage businesses my entire career, I have participated in many debates about whether entrepreneurs are born or made. What entices otherwise employable people to work for practically—maybe explicitly—nothing beyond the lottery system known as stock options (the tool Silicon Valley uses to lure young engineers into working crazy hours with no guarantees)? Now I learn that with jumping genes, natural selection is “rolling the dice” to build brains to meet the challenges of ever changing conditions. Yep, that sounds like an entrepreneur.

Michael J. Connelly
President Emeritus
New York Venture Capital Forum


In “The Far, Far Future of Stars,” Donald Goldsmith states that the luminosity of a star richer in heavy elements declines because of opacity of its outer layers. Then, in the next sentence, he goes on to say that “the lower luminosity means that the star consumes its nuclear fuel at a lower rate.” So what is it, opacity or lower rate?

Also, one expects that the trapping of radiation by the outer layers would cause the temperature to increase and, consequently, the fusion rate to increase as well. So what is going on?

Dov Elyada
Haifa, Israel

GOLDSMITH REPLIES: Stars produce energy in their cores, which passes to their surfaces and radiates into space. The lower luminosity results from a higher opacity, which hinders the passage of radiation. A lower luminosity also implies a lower rate of energy production and thus a slower consumption of nuclear fuel. The higher opacity that leads to a greater trapping of radiation produces complex effects in a star's atmosphere, including a possible increase in its size and temperature, but it is the temperature in the core, not in the atmosphere, that determines the star's rate of energy production.


“Lifting the Black Cloud,” by Robin Marantz Henig, succinctly and correctly sums up the state of evidence regarding the efficacy of antidepressant medications in saying that they “leave a lot to be desired”.

There are other alternatives. High-quality randomized controlled trials have shown that aerobic exercise reduces depressive symptoms in cancer survivors and in other populations. In contrast to the common side effects of antidepressants—such as sexual dysfunction, headaches, insomnia and nausea—those of exercise are a pure delight—enhanced libido, better sleep, decreased body fat, longer life, increased strength and endurance, and more. Exercise has the added benefit of low cost and may be modified to match individual needs. Must solutions to the black cloud of depression always be medicinal?

Blair T. Johnson
Linda S. Pescatello
University of Connecticut

One of the possible new treatments discussed in the article targets inflammation. Immune system–modulating products of this type can have the unwanted side effect of allowing latent infections to resume activity. And not just latent infections but unsuspected active infections producing inflammation might be involved, so interfering with the immune system will have consequences. Some investigators are looking at the connection between microbes and mental illness. Syphilis is well known as an agent of psychiatric symptoms, and a number of other germs may be as well. In those cases, you would want to recognize and treat the infection, too.

Linda Finn
Gainesville, Ga.


“A Neglect of Mental Illness,” by the Editors [Science Agenda], states that “all of us should get over the stigma we still tend to attach to” conditions of mental illness.

Was this an intentionally ironic play on words? Isn't the typical, uneducated and frustrating response to mental illnesses, such as depression, to believe sufferers should just “get over it”? Mental illness is not something one can just get over, nor can intolerance, misunderstanding and fear be overcome that way.

Acceptance and a positive, proactive approach to mental illness can be achieved through education. This article not only missed a teachable moment but did so by opting for a phrase that is universally unappreciated by those suffering mental illness.

Marie Smith
via e-mail


In “Time to Kill Off Captchas” [TechnoFiles], David Pogue argues that variants of the Captcha system used to filter out hacker and spammer programs (bots) from Web sites, including the newer reCaptcha, waste too much of users' time.

ReCaptcha successfully blocks hundreds of spambot attacks on my guest book page daily. No legitimate visitor to the site has ever complained to me about it. I am also 63 years old, wear bifocals and usually surf the Internet on an eight-year-old laptop with a 1,280- by 800-pixel screen. It is very rare that I encounter a Captcha image I cannot decipher, and I almost never have to refresh the image more than once to get one. This leaves me puzzled at the complaints of younger Web surfers who have, presumably, better eyes and better equipment.

So far the only countering move the spammers have come up with I am aware of is to hire Bangladeshis to sit at terminals all day solving Captchas. Because that costs them money, it removes the main incentive for spamming. The problem is thus much smaller and manageable with simple filtering. Further, if anyone ever did come up with an automated solution for Captchas, they could file for a patent on their algorithm and generate more income by licensing it for legitimate optical character recognition use than their spamming activities could hope to gain them.

It would be nice if there was another, better, less bothersome solution to the problem of spambots, but for now there isn't. We use Captchas because they work. They are not the only solution against spambots, but they are the most effective one. Until a way is found to block spam messages or identify them by their source (which would require a major revision of the Internet protocols), we are going to be seeing Captchas. At this time, the alternative is much worse.

Jerry Hollombe
via e-mail