Historian Dan Smail wants his colleagues to push the clock back - way back.

DAN SMAIL, a medievalist who arrived last month at Harvard's history department, is a time revolutionary. Historians, Smail says, are in thrall to a chronology of the human race that is, by now, embarrassingly out of date. He wants to move the start date of introductory history courses back, oh, 100,000 years or so.

If you have taken the first part of a two-semester, college-level history survey class, you know how it usually starts: a few desultory comments about ''prehistory" and then a pronouncement that civilization as we know it had its first stirrings in the Fertile Crescent, around 4,000 to 6,000 BC. But as Smail points out in an article in the latest issue of the American Historical Review, when you consider recent (and not-so-recent) discoveries in archeology, anthropology, and biology -- the finding that all humankind traces to Africa, for example, or that humans were on the march out of that continent by roughly 100,000 BC, not to mention good guesses for when language, hunting, and farming arose -- the fixation on a start date of 4,000 to 6,000 BC begins to seem awfully arbitrary.

And yet, as Smail goes on to argue in his essay, suggestively titled ''In the Grip of Sacred History," this chronological tick has a very interesting back-story. ''Every history curriculum in secondary schools and colleges that tacitly accepts a Near Eastern origin around 6,000 years ago," Smail writes, ''contains the unintended echo of the Judeo-Christian mythology of the special creation of man in the Garden of Eden."

Through the 18th century and well into the 19th, Western historians, almost all of them Christian, thought that humankind (and Earth) dated to roughly 4,000 to 7,000 BC. (One especially influential estimate pinpointed 4,004 BC.) And many thought that the Garden of Eden could be traced to the Fertile Crescent. Smail's theory is that, in the 19th century, as the biblical timeline lost credibility and the staggering age of the Earth began to be glimpsed, historians reflexively clung to as much of the traditional timeline as they could. A true reckoning with the long timelines envisioned by Darwin never occurred.

Smail is among a small but growing number of historians who think their field needs to push the clock back. Another key figure is David Christian, who teaches at San Diego State University. His 2004 book, ''Maps of Time: An Introduction to Big History," starts with the Big Bang and, in a book of 15 chapters, doesn't get to humans until Chapter 6.

For his part, Smail says his interest in the full sweep of the human story -- he calls it ''deep history" -- came partly from his bedtime reading: books like ''Africa: A Biography of a Continent," by the British writer John Reader (not an academic), and the inescapable ''Guns, Germs, and Steel," by the physiologist and geographer Jared Diamond. ''This is fun -- why isn't it history?" Smail thought. John McPhee's meditations on ''deep time" in his trilogy on geology was another background inspiration, as was a course taught by Smail's late father, John R.W. Smail, a historian at the University of Wisconsin, called ''A Natural History of Man" -- a favorite of students.

At Fordham, from which Harvard plucked him, Dan Smail offered a course on natural history in addition to courses on the Middle Ages, but his current schedule won't allow him to teach a deep-history course at Harvard until fall 2008. His next book, for the University of California Press, will be a manifesto in favor of the deep-history perspective, possibly followed by his own attempt to write a history integrating the story of human evolution with ''ancient" and modern world history.

Of course, whether to kick off History 101 in 100,000 BC (or earlier) is one question; whether evolutionary perspectives are useful to modern historians is a separate one. ''I'm not sure I see the payoff in how we understand the commercial revolution of the 12th century or the industrialization of the 18th to 19th centuries," objects Patrick J. Geary, a UCLA historian who has heard Smail present his work.

And the suggestion that the traditional Western Civ chronology is crypto-Christian is especially contentious. There are certainly nonbiblical reasons to stress the period circa 4,000 BC, as Barbara H. Rosenwein, chairwoman of the history department at Loyola University Chicago and coauthor of a popular textbook called ''The Making of the West," points out. The word civilization comes from the Latin word for city, and what can confidently be called cities first appear in the Fertile Crescent around then. That cities (and, slightly later, writing) came into being roughly when Christians used to think that the world was born might just be a nice coincidence.

Yet Smail points out that historians no longer think history is solely the stuff of cities, empires, or written documents, so arguments for 4,000 BC that rely on those things have a curiously old-fashioned cast.

At this point, reliance on the ''short chronology," as Smail calls it, may just be habit. Since it obscures so much -- for one thing, humanity's common origins in Africa -- it may be past time to give it up.