This is an explanation for passage 3 of LSAT preptest 62, the December 2010 LSAT – the comparative passage. The passages are about dental caries. The first passage discusses how agriculture leads to more caries because of greater consumption of carbohydrates. The second passage introduces some subtleties: agriculture and carbohydrates do not always lead to caries.
This section has paragraph summaries and an analysis of the passage, links to the explanations for the questions are below.
- Tooth decay lets us know when a population started agriculture.
- Carbohydrates lead to more caries. Carbohydrates come from agriculture.
- Some non-agricultural populations ate foods that decayed teeth.
- Researchers found 2,000 years worth of skeletons in Thailand. Over the 2,000 years, the prehistoric people gradually switched from hunter-gathering to agriculture.
- Agriculture causes caries. There is more sticky-starch, and less fiber.
- Over time, the diet had rice and yams. Both are carbs, so in theory they cause caries.
- Yet caries didn’t go up. They may have eaten more rice, which is less cariogenic.
There is one word in this passage you must understand: caries.
I doubt you’ve heard it before, unless you went to dental school. Most people read these passage with no idea what “caries” means. So every five lines the passage throws them a word they don’t understand, and they get very confused.
This is the wrong way. When you see a word you don’t know, AND that word seems important, stop! Read around the word for context. Try to understand it.
In this case, the passage actually defines caries for you. Look at line 1: “dental caries (decay)”. Let’s turn this into a simpler word. In three steps, I’m starting with the original term, then substituting words you know.
- Dental caries
- Dental decay
- Tooth decay
So “caries” in this passage = tooth decay. Every time you read the word “caries”, you should replace it with “tooth decay”.
Both passages are much easier if you understand this. Passage A says “Agriculture and carbs cause tooth decay, though tooth decay can happen without agriculture.”
Passage B says “One example in Thailand shows that additional carbs don’t always lead to tooth decay”.
You don’t need to memorize details, but you should know where they are
I don’t memorize all the details in these passages. For example, paragraph 2 in passage A has the evidence of tooth decay in agricultural populations. If a question asks, I know to look there. But I don’t retain all the information.
Likewise, paragraph 2 of passage B has technical information on how carbs can cause tooth decay. Great! If a question asks, lets look there. Otherwise, who cares.
I do retain a few details. I remember fiber is protective somehow, but can be bad. If a question asked about it, I would reread that section to learn the rest. I know where the passage talks about fiber, and that’s the important part.
Have a look at the paragraph summaries I made of both passages, above. That’s about all you have to know and understand. If you’re still confused about the passage, I recommend you reread it while keeping in mind that caries = tooth decay.
Tooth wear is not caries. Tooth wear is only mentioned in paragraph 2 of passage B. It’s caused by fiber, and it can be helpful in preventing caries.
Note: I’ll repeat the advice I gave for Passage 1. If you had trouble understanding this passage, then I recommend you go to the library, and get 20-30 back issues of the Economist. Then read their science section. Each issue has 2-3 pages of science.
The Economist’s science section is very well written. It doesn’t dumb down the science, but it’s written at a level that an intelligent non-scientist can understand. If you read many of these articles, you’ll develop a base of general scientific knowledge that will serve you well on all science passages.
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