The disadvantaged genius theory:
In general, the younger people are the more they rely on advisers and family for help getting into top schools, and the older they are the more self-reliant. I suspect that part of the reason Ivy medical schools are taking candidates from non-Ivy undergraduate schools, is that there are super intelligent people who, as teenagers, lacked the advising/resources necessary to get into a top school.
Think of all the first-generation college students from the middle of nowhere, kids without parents from poor neighborhoods, etc. Then they go to undergraduate school and get more resources and time to learn about graduate school, or they go to Student Doctor Network, find out what Ivy's care about (and why they matter), and end up getting in. Or they simply learn that they have a chance at getting into an Ivy, and that you don't have to be related to a past president of the USA to go to one, and therefore try applying in the first place (which is sort of a rumor).
For anyone in their 30's, I would count the development of the internet as another reason a highly intelligent person would have more resources or advising now than when applying to undergrad.
Of course if your parents did go to Harvard, they might know exactly how Harvard evaluates candidates, and use that knowledge to benefit you and your siblings = a huge advantage.