Mr. Nassirian said people at the Education Department had described the omission as “a clerical mistake.” But it is “odd,” he said, because applying the subject codes “is a fairly mechanical task. It is not supposed to be the subject of any kind of deliberation.”

“I am not at all certain that the omission of this particular major is unintentional,” he added. “But I have to take them at their word.”

Scientists who knew about the omission also said they found the clerical explanation unconvincing, given the furor over challenges by the religious right to the teaching of evolution in public schools. “It’s just awfully coincidental,” said Steven W. Rissing, an evolutionary biologist at Ohio State University.

Deleting something from a document in Word is an accident, but very easy to correct. If you look at the PDF, 26.1303 is simply gone. That's not an "accident."