Jumat, 26 September 2008
Carbon Sequestration
A currently feasible technology for sequestering carbon so that it can't contribute to global warming is to store it deep underground. Take a look at the procedure used at Statoil of Norway’s Sleipner West gas field. Statoil is storing 2,800 tons of CO2 deep underground every day, in what is currently the largest carbon sequestration project in the world. Their website has a nice animation that shows the chemical process for separating the CO2 from natural gas, as well as a good reference article that your students could read and understand. We talk about carbon sequestration in the upcoming 5th edition of Human Biology, in the Current Issue on global warming (pp. 556-557).
Rabu, 24 September 2008
A Screening Test for Ovarian Cancer?
Here’s an ethical dilemma for you:
A promising new screening test for ovarian cancer called OvaSure can correctly identify ovarian cancer 95% of the time. Ovarian cancer is one of the most deadly cancers if it is not detected early. The company marketing the test says that the test has a false-positive rate of only 0.6%. (A false-positive is when the test indicates that cancer is present when in fact it is not.) Should the test be made widely available as a screening test for ovarian cancer?
Let’s see; 95% success rate at detecting ovarian cancer versus a 0.6% false-positive rate – it doesn’t sound like much of a dilemma, does it? You might try it out on your students to see what they think. But it is an interesting dilemma, and the reason is that ovarian cancer is rare; its prevalence is only about 0.06%. So among 100,000 women screened with the new test, 60 (0.06% of 100,000) would have ovarian cancer and 57 of them (95%) would be diagnosed correctly. Many of these 57 might be saved. However, 600 women (0.6%) would be told they had ovarian cancer when they did not. In the absence of any good corroborating tests to confirm the diagnosis, many of those 600 women might choose to have a surgery they actually didn’t need. And almost certainly they'd suffer emotionally from the belief that they had a deadly cancer.
Sometimes you have to run the numbers carefully to see the full effect of what is being said. It pays to be a skeptic.
ADDENDUM: Ovasure was pulled from the market in October, 2008, after the FDA sent the company a letter saying that the kits required FDA approval before they could be marketed and sold.
A promising new screening test for ovarian cancer called OvaSure can correctly identify ovarian cancer 95% of the time. Ovarian cancer is one of the most deadly cancers if it is not detected early. The company marketing the test says that the test has a false-positive rate of only 0.6%. (A false-positive is when the test indicates that cancer is present when in fact it is not.) Should the test be made widely available as a screening test for ovarian cancer?
Let’s see; 95% success rate at detecting ovarian cancer versus a 0.6% false-positive rate – it doesn’t sound like much of a dilemma, does it? You might try it out on your students to see what they think. But it is an interesting dilemma, and the reason is that ovarian cancer is rare; its prevalence is only about 0.06%. So among 100,000 women screened with the new test, 60 (0.06% of 100,000) would have ovarian cancer and 57 of them (95%) would be diagnosed correctly. Many of these 57 might be saved. However, 600 women (0.6%) would be told they had ovarian cancer when they did not. In the absence of any good corroborating tests to confirm the diagnosis, many of those 600 women might choose to have a surgery they actually didn’t need. And almost certainly they'd suffer emotionally from the belief that they had a deadly cancer.
Sometimes you have to run the numbers carefully to see the full effect of what is being said. It pays to be a skeptic.
ADDENDUM: Ovasure was pulled from the market in October, 2008, after the FDA sent the company a letter saying that the kits required FDA approval before they could be marketed and sold.
Jumat, 19 September 2008
Gender Selection Nears Perfection
In Human Biology 5th ed., pp. 396-397, we talk about some of the ethical and technical aspects of gender selection of a baby, and we mentioned sperm sorting followed by artificial insemination as a way of increasing a couple’s chances of having a boy to over 75%, a girl to over 90%.
Well, if those odds still aren’t good enough, now gender can be selected with essentially 100% accuracy. Basically, it’s a variation of the standard in vitro fertilization (IVF) technique: 1) harvest eggs from a woman according to the standard IVF protocol, 2) fertilize the eggs in vitro, 3) grow the embryos to the 8-16 cell stage, 4) Remove a cell for DNA analysis to determine the presence or absence of the Y chromosome, 5) implant only embryos of the desired sex. Bingo, it’s a girl! (Or a boy).
Removing a cell for DNA analysis doesn’t affect the ultimate development of the fetus because at that stage none of the cells have begun to differentiate. In fact IVF with DNA analysis is already being done to screen out certain rare but debilitating genetic diseases, where the risk of these diseases is considered high. But before a couple chooses to use it to select gender, they should consider that it’s expensive, it’s invasive, and some would say it goes against nature.
Where do your students stand on this? Are they aware that there are clinics advertising on the Internet that are routinely doing it? (Google “IVF” and “gender selection”).
Well, if those odds still aren’t good enough, now gender can be selected with essentially 100% accuracy. Basically, it’s a variation of the standard in vitro fertilization (IVF) technique: 1) harvest eggs from a woman according to the standard IVF protocol, 2) fertilize the eggs in vitro, 3) grow the embryos to the 8-16 cell stage, 4) Remove a cell for DNA analysis to determine the presence or absence of the Y chromosome, 5) implant only embryos of the desired sex. Bingo, it’s a girl! (Or a boy).
Removing a cell for DNA analysis doesn’t affect the ultimate development of the fetus because at that stage none of the cells have begun to differentiate. In fact IVF with DNA analysis is already being done to screen out certain rare but debilitating genetic diseases, where the risk of these diseases is considered high. But before a couple chooses to use it to select gender, they should consider that it’s expensive, it’s invasive, and some would say it goes against nature.
Where do your students stand on this? Are they aware that there are clinics advertising on the Internet that are routinely doing it? (Google “IVF” and “gender selection”).
Jumat, 12 September 2008
Irradiation of Foods
Would your students buy lettuce and spinach that had been irradiated in order to kill micro-organisms such as E. coli and salmonella? In fact, the government has already approved of the practice. Irradiation of oysters, beef, poultry and eggs has been allowed for some time now, but irradiation of lettuce and spinach is fairly new.
Until now the market for irradiated foods has remained small because current FDA regulations require that irradiated foods be labelled as “irradiated” and display an irradiation logo. The labels have convinced some consumers that irradiated foods may be radioactive (they’re not). To encourage consumer acceptance, the FDA has proposed changes to the labelling rules so that in the future, irradiated foods would only have to be labelled as “cold pasteurized”, or simply pasteurized.
How accurate are your student’s perceptions about food irradiation? How many of them mistakenly believe that irradiated foods are radioactive? The safety of food irradiation might make a good out-of-class research project or topic for discussion.
Until now the market for irradiated foods has remained small because current FDA regulations require that irradiated foods be labelled as “irradiated” and display an irradiation logo. The labels have convinced some consumers that irradiated foods may be radioactive (they’re not). To encourage consumer acceptance, the FDA has proposed changes to the labelling rules so that in the future, irradiated foods would only have to be labelled as “cold pasteurized”, or simply pasteurized.
How accurate are your student’s perceptions about food irradiation? How many of them mistakenly believe that irradiated foods are radioactive? The safety of food irradiation might make a good out-of-class research project or topic for discussion.
Senin, 08 September 2008
Strong Hurricanes Get Stronger
This week marks the peak of the hurricane season for 2008. And a new study just published in Nature shows that the strongest hurricanes are getting stronger. The strongest storms now have peak wind speeds that average 16 miles/hour faster than back in 1981 (see “The increasing intensity of the strongest tropical cyclones.” Nature Sept. 4, 2008, pp. 92-95.) The article is not suitable for students, however, unless they have a strong background in statistics.
Over the same time period (1981-2006), the sea surface temperatures have risen by 0.5 degrees Fahrenheit. Most climatologists believe that warmer waters are certain to lead to stronger storms, because hurricanes derive their energy from the heat of warm surface waters.
Over the same time period (1981-2006), the sea surface temperatures have risen by 0.5 degrees Fahrenheit. Most climatologists believe that warmer waters are certain to lead to stronger storms, because hurricanes derive their energy from the heat of warm surface waters.
Kamis, 04 September 2008
Bird Flu: The Pandemic That Hasn't Happened (Yet)
When was the last time YOU thought about bird flu? These days the public and the news media are treating the continued threat of a worldwide pandemic with a great big yawn. Bird flu is so yesterday!
Here’s an interesting exercise you could give your students: Ask them to search a key phrase such as “bird flu”, “avian influenza” or “H5N1” in any major newspaper with a searchable archive (such as the New York Times), arrange the retrieved documents by date, and count them. I searched “avian flu” in the New York Times recently and found that references peaked at 181 in 2006 and have since fallen to a paltry 18 in the first eight months of 2008.
Psychologists surely would have something to say about how long we can sustain our fear of a perceived threat that doesn’t materialize quickly. Health officials worry that if we become convinced that bird flu is not a threat any more, we will begin to make political and economic choices that direct our resources away from preparedness programs. And no one knows whether or not that would be a good idea at this point.
What do you think?
Here’s an interesting exercise you could give your students: Ask them to search a key phrase such as “bird flu”, “avian influenza” or “H5N1” in any major newspaper with a searchable archive (such as the New York Times), arrange the retrieved documents by date, and count them. I searched “avian flu” in the New York Times recently and found that references peaked at 181 in 2006 and have since fallen to a paltry 18 in the first eight months of 2008.
Psychologists surely would have something to say about how long we can sustain our fear of a perceived threat that doesn’t materialize quickly. Health officials worry that if we become convinced that bird flu is not a threat any more, we will begin to make political and economic choices that direct our resources away from preparedness programs. And no one knows whether or not that would be a good idea at this point.
What do you think?
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