"The commitment that's required--at least of lab courses--in the sciences for the same credit is just greater," he says.
Buell also attributes the disparity to other factors, including the differing motivations of students taking science and non-science classes.
"There are more students taking science courses as semi-captives, and not seeing science as a vocation," he says.
Buell adds that quantitative courses "open a kind of scale of performance ability between the top and the bottom."
"A standard image of that is the math genius. That has no counterpart in the humanities. If you're self-identified as not a math genius," then it is difficult to succeed, he says.
Other professors contend that the gap between science and non-science grades has leveled off.
According to Pilbeam and Assistant Dean for Undergraduate Education Jeffrey Wolcowitz, the current disparity in grades between science and non-science courses appeared about 10 years ago, but since then, grades have "inflated more or less in parallel."
Indeed, Kishlansky contends that "grade inflation has struck everyone equally."
Causes of Grade Inflation
Different professors have theories about the sources of grade inflation as diverse as Harvard's student body itself.
Kenan Professor of Government Harvey C. Mansfield Jr. '53 sparked controversy four years ago when he suggested in Harvard Magazine that grade inflation was linked to the institution of affirmative action in 1969.
Pilbeam attributes grade inflation to increased "fraternization" between the Faculty and students.
"The change in the dynamic between the generations is not a bad thing, but it doesn't come unencumbered," Pilbeam says.
Pilbeam says the problem is "more likely to happen in small classes or tutorials."
"We want professors to be able to say to a student in a one-on-one tutorial, 'Even though you've shown up every week, and done all the reading and had nice conversations, you can still get a B-,'" he says.