> This is arguably rational because the pool is small and there's little to gain by studying harder if you already have a perfect GPA.

So there is a low ceiling, and if they instead used MCAT or something with a higher ceiling (where, apparently, the number of perfect scores is about 50 per year—in America, presumably lower in Canada due to population size), then studying harder would benefit them. That seems like a much better outlet for competitive urges.

But also, how small is the pool of qualified applicants? If there were something like "they're going to take n people from your school, at which there are 30 plausible candidates", then sabotaging one might conceivably be worthwhile. But if the pool is—well, Google says 3,000 medical students get accepted each year in Canada (and the qualified applicant pool is presumably at least somewhat larger), and sabotaging one person is extremely unlikely to help you personally. (This is one case where it's good that the expected-value "benefits", of sabotaging person X, are widely distributed among thousands of medical candidates, and thus it's a "free-rider problem" where no individual candidate has a strong motivation to do the work.)

Is there some multi-stage thing where they pick 10 people from each high school, or 30 from a town, or something? Or is there major grading on a curve, or a big benefit for being the top person in your classroom of 15? That seems like how you would get real incentives for this backstabbing behavior. Otherwise, I can't see how it's rational (even to a complete sociopath), and would have to chalk it up to individual miscreants and possibly some kind of culture that encourages it in other ways.

> Or is there major grading on a curve, or a big benefit for being the top person in your classroom of 15?

Yes. UofT even has "down curves" where your mark is lowered to ensure the correct distribution.