<p>In regards to the 3 (I didn't actually check it) Harvard undergrads enrolled in the Harvard PhD program, 3 out of 18 is indeed a very high representation. Considering the vast number of colleges in the U.S. alone, having a single university contribute to 17% of the class is indeed striking, if not "incestuous."</p>
<p>This list of Harvard physics PhDs seems to support an even more positive correlation with undergrad and graduate studies:</p>
<p>Harvard</a> Physics Department - PhD Theses: 2000 to present </p>
<p>You'll find much more than three there.</p>