Aggressive "weed out" policies?

[cobrat]

However, the level of weeding differs. While a 3.0 GPA student is extremely unlikely to get into a US MD medical school, a 3.0 GPA student is likely to be able to enter and stay in natural science majors at most colleges and universities that offer those majors.

True.

However, it can be quite a sobering experience to find out you’re one of the minority in your intro natural science class who did well enough to even continue in the major.