<p>That is not true at all for most departments at MIT. </p>
<p>At MIT, you have a significant advantage as an undergrad majoring in a department when applying to the same department for grad school. The reason for that is fairly straightforward. Graduate admission decisions are made at the departmental level. If you have established a good rapport with the professors and done research in the department, they know you well and will generally be more than happy to recommend you for admission to grad school. If the prof runs a big lab, as many do, his recommendation may be all that is required to get you admitted. His colleagues in the department won’t overrule him. </p>
<p>Let’s face it. MIT has some of the very best undergrad science and engineering students anywhere. The school would be stupid not to admit them for grad school. On top of that, the students are already familiar with the research being done. In departments depending on large outside grant funding, it is a huge advantage to have an already trained pool of talent. Quite a few departments have a disproportionate number of MIT undergrads, especially the most selective ones such as EECS or the Media Lab. </p>
<p>The only departments I am not sure about are the humanities departments such as philosophy, political science or economics, all very prestigious. These are fields where there are different “schools of thought” and the departments may want their PhD students to have a diversity of backgrounds. To the extent that is also the policy at MIT, I am not sure. I would venture that if you are good they will want to keep you. As far as science or engineering, it is only an advantage to have an undergrad degree from MIT. The list is long with students have done their BS, MS and PhD at MIT. Some even join the faculty and become “lifers”. MIT is a very incestuous place!</p>