Critical thinking Acknowledment Dr Alison Campbell University of Waikato
Scholarship criteria The student will use biological knowledge and skills to analyse biological situations and integrate ideas into a coherent response. For “outstanding performance”, the student will demonstrate perception and insight in the analysis and integration. (Biology Scholarship standard, Ministry of Education)
Scholarship students are expected to demonstrate high level critical thinking, abstraction and generalisation, and to integrate, synthesise and apply knowledge, skills, understanding and ideas to complex situations. (Scholarship Performance Reference Group)
The three examples shown represent just some of the diversity found in bony fish. Use the diversity of the fish and/or any other named group(s) to discuss the following statement: ‘Diversity is the end product of evolution.’
Candidates who did not achieve the standard tended to describe rather than discuss in Question 3, and while there were a lot of descriptions of the diversity in fish, there was little or no attempt made to discuss the evolutionary processes that resulted in this diversity. Candidates gave their own opinion as an evaluation.
Overall: Successful candidates addressed the question asked, with minimal irrelevant material presented. Answers were coherent with ideas integrated, and it was clear these candidates spent time planning their answers and organising their ideas. Unsuccessful candidates wrote in generalisations rather than specifics e.g. “it evolved by natural selection”. They tended to use inappropriate descriptors e.g. “catastrophic”, “terrible”, rather than biological terms.
Critical thinking means seeking reliable knowledge. Many students fail to assess the reliability of information to which they are exposed in everyday life, let alone pursue the dissection of scientific literature. And many people are deceived and defrauded by pseudoscience. Practice in critical thinking prompts thoughtful examination of the role of science in society.
Wind farms & bird kills: In the United States (where some of the earliest wind farms were poorly sited in areas where there were lots of bird movements), a study shows that between 10,000 and 40,000 birds are killed by turbines each year. This seems like a lot – and a good reason to reconsider the use of wind farms…
However, you need to consider the other causes of bird deaths. In the US: cars & trucks kill 60 – 80 million birds per year; buildings/windows kill 98 – 980 million per year; communication towers kill 4 – 50 million per year; the biggest killers of birds are domestic & wild cats, which are estimated to kill up to a billion birds every year. Environmental scientists in NZ say that as long as care is taken about where we site wind farms, they present only a very small danger to birds & bats.
Many people can’t drink milk, due to an allergy or intolerance. However, milk contains a lot of nutrients - & so the r.d.a. is 2 servings/day for an adult. Still, for some people it’s quite harmful – if they can’t tolerate milk (or any food) they shouldn’t eat it just because it’s in the “healthy foods” pyramid! In other words, evaluate by the principle of individuality: by your own uniqueness.
However, someone may become quite sick after a glass of milk. Instead of properly evaluating the situation and saying "I should not drink milk," they instead overgeneralise and say "Milk is bad... no one should drink milk." This is overgeneralising from personal preferences. The principle of individuality will help to counteract this tendency to evaluate a person, or group of persons, or a food, as being all bad or all good and then projecting our expectations onto all our encounters with this person or food.
Or look at Vitamin A: it’s a "vitamin" & so it must be good for us! This is a common perception. However, Vitamin A can be lethal. The recommended daily dose of Vitamin A is around 1,000 Retinol Equivalents each day: Ingesting 5 REs a day will eventually lead to death from Vitamin A deficiency. Taking in 100,000 REs a day will lead to hypervitaminosis A … & eventual death.
Many people have made themselves sick and even killed themselves by disregarding the individuality of dose. A little may be good for you, but a lot may kill you. Even plain water can kill you if you drink too much.
Saccharin is a non-calorie sweetener widely used in foods since World War I. Up until the 1970s many diabetics & weight watchers used saccharin as a sugar substitute. A 1977 study of rats found that saccharin could cause cancer. The FDA banned saccharin from the food supply, & though this has since been reversed many people remain fearful of saccharin.
BUT: Saccharin has been found to cause cancer only in one species – rats. It does not affect many other species, such as monkeys, mice and guinea pigs. Among rats, saccharin caused an increased incidence of bladder cancer in male rats, but not in female rats. Yet the media focussed on labelling saccharin a "carcinogen" without reference to species, as if a carcinogen in rats will automatically be a carcinogen in humans.
By 1990, 392 chemicals had been tested for carcinogenicity in both mice and rats. 226 were found to cause cancer in at least one species; however 42% of these carcinogens caused cancer in ONLY one of these species! There is clearly significant variability between species in cancer risks. If nearly half the known rodent carcinogens can't be generalized from one rodent species to another, how can we confidently generalize from male rats to humans?
The media also tend to overgeneralise between reporting of "carcinogens" and the way we test chemicals for carcinogenicity. The rats in the saccharin experiment received the equivalent of someone drinking 800 cans of diet coke every day! This high dose was selected so that relatively few animals could be used. BUT a substance may have different effects at different doses. No human would drink anywhere near that amount of saccharin in one day, let alone each day for their entire life!
However, the media reported the study as if the dose were irrelevant. In fact, several essential nutrients in humans, including selenium and retinol (a form of Vitamin A), cause cancer when fed in high doses to some animal species. If we applied saccharin standards to these essential nutrients they would have to be banned from the human food supply.
In 1989 came the announcement that dioxin had been found in milk served from paper cartons. The dioxin had leached from the paper cartons into the milk. Newspaper stories of the dioxin-tainted milk invariably referred to dioxin as a carcinogen, implying that increased incidence of cancer would await the children exposed to the tainted milk. However: Dioxin had been found to be a carcinogen in some animal species, but not in others. And it had been found to decrease the risk of some types of cancers in some species. Dioxin, in other words, could just as truthfully be called an anticarcinogen.
A second media over-generalisation involved the amount of dioxin in milk: Most milk samples tested revealed no detectable dioxin, but the highest amount of dioxin in a tainted sample was measured at 0.07 parts per trillion (ppt). 0.07 ppt is equal to 70 nanograms of dioxin in 1200 litres of milk.
In a 1998 experiment, rats were fed GM potatoes: the potatoes contained a gene from snowdrops that expressed the protein lectin. Lectin can act as a natural pesticide. The researchers fed groups of rats one of these menus: lectin-boosted modified potatoes, unmodified potatoes, or unmodified potatoes plus lectin from a bottle.
What the study found: Eating potatoes with lectin (in any form) was associated with a thickening of the mucus membrane lining the stomach. In rats that ate only raw genetically modified potato, the mucus-producing pits of the small intestine were longer, compared to other rats in the study. Rats eating transgenic potatoes had fewer lymphocytes compared to those eating normal potatoes.
The scientists’ conclusions: Eating potatoes modified to produce lectin caused some cells to grow, and others to fail to grow, in the stomach and intestine. At least some of these effects were due to the foreign gene. Other effects could be due to the process of genetic engineering itself. The genetic modification process could cause similar outcomes when used to move other genes.
Rats & GE diets – what was wrong with this study? Too few rats – only six per food type – were used. Poor diets: all the rats ate pure potatoes, which contain only 6% protein (normal lab rats get 15%). "There is convincing evidence that short-term protein stress and starvation impair the growth rate, development, hepatic [liver] metabolism and immune function of rats." There was no control group – no group of rats ate a good rat diet for comparison. Critics maintain that “no consistent patterns of changes were observed” during the study.
1.Discuss techniques that scientists could use to detect DNA damage in microbes. What key factors would have to be considered? Use diagrams if necessary. This question is testing the application of certain genetic and other techniques and the ability to consider key factors in designing experiments. This tests some of the skills of practical investigation.
2.The safety of food irradiation is a controversial issue in New Zealand at the moment. There is not enough information given above to fully evaluate this issue. What questions would you ask of scientific experts and what information would gather before you could make an informed choice as to whether food should be irradiated? This is testing the skills of evaluating issues. The first thing to work out here is the key issues highlighted earlier. Notice that you are asking questions, not necessarily answering them. The ability to know the questions to ask is a really important skill. Also, this is a science paper, so you will be wanting hard data!
Consider these questions under the following headings: (i)The effectiveness and safety of gamma rays. This question is about gamma rays. So immediately recall your knowledge about the penetration of gamma rays. Think about how the radiation source is used and how it is stored.
(ii) Consideration of the relative risks involved in irradiating food. This is testing the skills of writing a case study. Go through the passage carefully and consider the arguments for either side of this debate. Also consider relative risks, e.g. methyl bromide can be used for destroying exotic pests but it harms the ozone layer. So is radiation a better option here? Consider things like the incidence of food borne diseases – one question you may want to ask experts or find out more information about is how serious a problem this is. What else may you want to find out about?