Five Harvard professors were elected to the National Academy of Sciences (NAS) last week, marking the third straight year that the University took the most spots of any other institution.

Leverett Professor of Mathematics and Dean of Harvard College Dean Benedict H. Gross ’71, Tishman and Diker Professor of Sociology Lawrence D. Bobo, Howard Hughes Medical Institute investigator and Professor of Cell Biology Mark T. Keating, Hyman Professor of Chemistry Charles M. Lieber and Jackson Distinguished Professor of Clinical Medicine John T. Potts joined the 1,949 academics who are members of the prestigious organization.

“It’s a great honor to be recognized by others in the field,” said Gross, who studies number theory and the representation theory of groups. “The mathematicians who have been elected are really a distinguished group, and include many of my teachers and mentors.”

Bruce M. Spiegelman, a professor of cell biology at Harvard Medical School who was inducted into the NAS in 2002, said that 72 American and 12 international scientists are chosen every year as new members.

Current members of the NAS nominate potential new members in their own fields of study, and then narrow the nomination lists through a vote on specific fields, Spiegelman said.

The final list is voted on by every member of the NAS, irrespective of field.

“It’s the highest honor an American scientist can get short of the Nobel Prize. It means a lot because it’s your peers that vote on this,” Spiegelman said.

Spiegelman added, however, that the NAS election procedures are flawed, favoring physical scientists over life scientists because of strict caps on the numbers of researchers elected in each field in any given year.

“Election to the NAS is a bit unfair to life scientists because the number of elected members was set long ago, when the percentage of scientists who were in life science was much smaller,” Spiegelman said.

NAS member Laurie Glimcher, the Given Professor of Immunology at the Harvard School of Public Health and Professor of Medicine at Harvard Medical School, said that the organization ought to “look for more people in the life sciences.”

But Glimcher noted that physicists “probably would not be too happy” about the idea, and she said she does not expect a change in NAS election policies in the near future.

As it stands, the NAS nomination process is closed, and candidates are not notified that they are being considered for membership until the final vote.

“The news came to me as a total but delightful surprise. I had no idea my name was even under consideration,” said Bobo, the author of Racial Attitudes in America: Trends and Interpretations. “This is the sort of honor one might guardedly hope to achieve at a late stage in one’s career but never really expect to happen,” he said.

But Lieber said his election to the NAS would not have a large impact on his professional work.

“I guess it’s nice, but it’s not something to dwell on. It’s just an award, and you can take it seriously, or not,” said Lieber, who studies nanotechnology. “I do not know that much about the NAS and their mission. My personal goal remains in research [and] to work with my students to change the world for the better.”

Potts, who studies calcium metabolism and previously served as director of research at Massachusetts General Hospital, said that he was “very honored and very pleased” to receive the award.

Keating, who studies the genetics of organ regeneration, said he was “looking forward to signing Honest Abe’s book.”

The NAS, a nonprofit, was established in 1863 and charged by Congress and President Lincoln with advising the federal government on scientific policy. Harvard has the most NAS members of any university, with 156. Berkeley is second at 124, and Stanford is third with 119.

Bruce M. Alberts ’60, a member of the Harvard Board of Overseers, is currently the president of the NAS.

—Staff writer Risheng Xu can be reached at xu4@fas.harvard.edu.