Sunday, July 27, 2008

Why We Believe Anecdotal Evidence

Why do many people persist in believing that certain vaccinations may cause autism, despite the fact that there has never been any scientific evidence to support such a claim? Why is it that we continue to be suckers for all kinds of vague, unsubstantiated health claims for various herbs and food supplements? Michael Shermer, publisher of Skeptic magazine, thinks he’s found a reason. He hypothesizes that our willingness to believe in anecdotal evidence over objective data is hard-wired into our brains as a consequence of evolution. He argues that making a false positive error (believing that "A" leads to "B" when actually it does not) usually has no consequences – if you believe that a fruit is poisonous, choosing not to eat it only leaves you hungry. On the other hand, making a false negative error (failing to believe that "A" leads to "B" when in fact it actually does) can kill you - if you eat a poisonous fruit you may die.

What do you think? Read Mr. Shermer’s one-page opinion column in the August issue of Scientific American (“Wheatgrass Juice and Folk Medicine”, Scientific American August 2008, p. 42) and judge for yourself. This article might be a useful supplement for Chapter 1, Human Biology, 5th ed.

Tuesday, July 22, 2008

Losing the Battle Against Bacteria

Bacterial resistance to antibiotics is increasing and there are too few new antibiotics in the drug discovery pipeline. Nevertheless, more than half of the major pharmaceutical companies have shut down their antibiotics R&D divisions entirely within the last 20 years. Read about it in the current issue of Science (“The Bacteria Fight Back”, Science 321:356-361, July 18, 2008). The article documents the history and the biology of bacterial resistance to antibiotics. It also and suggests some reasons why pharmaceutical companies seem disinterested in developing new antibiotics, even as the human death toll rises.

This would be a good article to share with your students in support of the Health Watch box on page 18 of Human Biology, 5th ed. The article could also be used to kick off a class discussion of the economics of developing and selling pharmaceutical drugs.

Sunday, July 20, 2008

Human Drugs From Plants

Remember Cerezyme, that very expensive drug that can cost patients up to $300,000 per year? (See this blog, March 17, 2008.) Cerezyme is a human enzyme called glucocerebrosidase. It is missing in patients with a rare genetic disorder called Gaucher’s disease, found mainly in persons of Ashkenazi Jewish descent.

There may be good news for Gaucher’s disease sufferers soon. An Israeli company named Protalix Biotherapeutics has developed a protocol for producing recombinant glucocerebrosidase cheaply in large amounts. But they’re not using animals – they’re using genetically engineered carrot cells grown in cell culture in big plastic bags. The enzyme is already in Phase III clinical trials, meaning that it is being tested in human patients. If approved by the FDA it will be the first plant-made recombinant drug ever approved for use in human patients. This could be a breakthrough that leads to a whole new field in drug development – making drugs by inserting human genes into plant cells.

To read more about it and see a photo of the carrot cells in culture, go to Protalix’s website at

Thursday, July 17, 2008

Dieting is Not Very Effective

Confirming what many dieters already know, most diets don’t work all that well over the long term. In a study that just came out today, over 300 moderately obese subjects (average Body Mass Index; 31) were placed on one of three different diets for two years. Participants lost 10-14 pounds within five months, but then they stopped losing weight and even gained some of the weight back over the next year and a half. At the end of a full two years, participants had lost only 6-10 pounds on average – not a lot, considering they were obese to start with.

The study’s authors most likely were disappointed (the study was funded in part by the Atkins Foundation, and a low-carb diet was one of the diets tested.) But based on some observed changes in lipid profiles, they suggest that the diets may have conferred some health benefits to the participants despite the minimal weight loss. It’s an interesting hypothesis, but it’s certainly not a valid conclusion at this point.

Reference: “Weight Loss with a Low-Carbohydrate, Mediterranean, or Low-Fat Diet”, The New England Journal of Medicine 359:229-241, July 17, 2008.

Tuesday, July 15, 2008

Paths of Human Migration

Scientists are now able to trace the routes taken by the ancestors of modern humans as they migrated out of Africa by tracking small changes in fossil DNA. The route maps are surprisingly complete - it almost seems as if prehistoric humans were walking on superhighways at super-slow speeds. In actual fact, they stopped and established colonies along the way, staying in one place for generations when conditions were right for human habitation. Modern humans finally reached South America roughly 40,000 years after their ancestors first left Africa - that's an average speed of less than 1/2 mile per year. The route took them across the Arabian peninsula, over Asia to Siberia, across a narrow land bridge to Alaska, and then south across North and Central America.

The techniques for tracing human migrations and the various routes taken are documented in “Traces of a Distant Past” (Scientific American, July 2008, pp. 56-63.) This would be a great paper to share with your students when you're discussing human evolution.

Sunday, July 13, 2008

Gardasil and Irresponsible Journalism

Last Monday the CBS Early Show ran a story about a 14-year-old girl named Jenny who is now nearly completely paralyzed by a degenerative mucle disease of unknown cause. It just so happens that she received Gardasil, the vaccine against human papillomavirus (HPV) 15 months ago, like so many other girls her age. Her parents spoke to CBS News with the hope that coverage of Jenny’s plight would help them find “comparables” - other patients with the same symptoms, so that her doctors could discern the actual cause of her disease. Nevertheless, CBS chose to run the online story with the more sensationalist headline, “HPV Vaccine Linked to Teen’s Paralysis?” (, July 7).

Four days later, FOX news went one step further with a story entitled “HPV Vaccine Blamed for Teen’s Paralysis” (, July 11).

This is biased journalism at its worst. Who exactly is blaming Gardasil for Jenny’s disease - Fox News? In fact the Fox News article is full of errors. For one, the article attributes to Jenny’s parents a statement made by a spokesperson for Merck, Gardasil’s manufacturer. In addition, the article uses the word “casually” in place of “causally”. For the record, what a Merck spokesperson actually said was, “We’re aware of this case and based on the facts that we’ve received, the information doesn’t suggest that this event was causally associated with vaccination.”

On their blog site on July 7 (see, the parents expressed disappointment with the CBS news coverage, saying “The family believes that there may be a link between Jenny’s health and the HPV vaccination……” “But, there is no medical consensus on whether this hypothesis is stronger than other possible explanations.”

Jenny’s parents are obviously scientifically literate. They know how to distinguish between a hypothesis and a scientifically justifiable conclusion. As you’re discussing the importance of being scientifically literate in your classroom, Jenny’s parents’ blog site and the two news articles would make interesting topics for discussion.

One final thought: Do you think that the biased news coverage of Gardasil could be intentional, given that conservatives don’t like the idea of a vaccine against a sexually transmitted disease being given to young girls? What do your students think?

Sunday, July 6, 2008

Your Cell Phone's Radiation Emission

Does the radiation emitted by cell phones cause brain cancers? Although most of the scientific evidence suggests that it doesn’t, the media always seems to find a physician or a patient or even a scientist who is willing to talk about it. The debate has been going on since cell phones first came out, and it’s not likely to go away any time soon.

Are you concerned? How much radiation does your cell phone emit, anyway – a lot, or a little? The Federal Trade Commission sets an upper limit of 1.6 W/kg (watts per kilogram) for certification, but commercial phones on the market vary all the way from 1.6 down to 0.14 – more than a 10-fold difference.

For a complete listing of the radiation output of all current phone models, go to, go to “Reviews - cell phones”, then click on “Cell phone radiation charts.”