<p>Of course it’s not a requirement, and nobody is suggesting that it is. Your undergraduate origin is not the most meaningful part of your application, and top graduate programs are not made up exclusively of students from top 20 undergrad schools.</p>
<p>Still, students from top 20 schools are heavily overrepresented in top graduate programs, and it’s hard to argue that a top undergrad origin isn’t helpful in a graduate application. The top feeder schools to my PhD program (by raw numbers, not even relative to the number of biology degrees awarded) over the past three years are MIT, Harvard, Princeton, and Yale.</p>