The key that Casaubon craved is particularly alluring. He wasn’t just tracing similarities; he was hunting for a primordial mythology, a long-lost ancestor dimly visible in its descendants. He happened to believe this original tradition was Christian truth, but set aside the apologetics and there’s still something intoxicating about the quest for a key: the notion that, by sifting through myth, we might retrieve the imaginative worlds of the earliest storytellers. Nor is the quest just a scholarly game; it’s an attempt to prove, against all odds, that our wild, warring species shares something irreducible at its core.

Nowadays, we can unearth bones, extract DNA, even map ancient migrations, but only in myths can we glimpse the inner lives of our forebears—their fears and longings, their sense of wonder and dread. Linguists have reconstructed dead languages. Why not try to do the same for lost stories? And, if we can, how far back can we go? Could we finally recover the legends of our earliest common ancestors—the ur-myths that Casaubon so desperately pursued?

If any field lends credibility to the dream of a Casaubonian key, it’s Indo-European studies. Where Frazer’s method was freewheeling, Indo-Europeanists are exacting. The discipline is usually said to have begun in 1786, when Sir William Jones, a colonial judge stationed in Bengal, addressed the Asiatic Society. Years of studying Sanskrit had convinced him that it closely resembled Greek and Latin—“indeed,” Jones said, “no philologer could examine them all three without believing them to have sprung from some common source, which, perhaps, no longer exists.” He suggested that Germanic and Celtic languages, as well as ancient Persian, might belong to this same lost family. Others had glimpsed such affinities before, but Jones did more than notice; he set off a scholarly chase, and a popular fascination, that has yet to run its course.

Today, it’s broadly accepted that languages as different as English, Welsh, Spanish, Armenian, Greek, Russian, Hindi, and Bengali descend from a single ancestor: Proto-Indo-European. Linguists have mapped how words spoken five thousand years ago have branched into the webs of vocabulary we know now. My first name, Manvir, for example, fuses two Sanskrit roots with clear European cousins: “man,” meaning “thought” or “soul”—related to “mental” and “mind”—and “vir,” meaning “heroic” or “brave,” as in “virtue” and “virile.”

But reconstruction didn’t end with nouns and verbs. Gods dance on our tongues, and, as scholars compared Indo-European languages, they found striking mythological congruences, too. The British journalist Laura Spinney, in her recent book, “Proto: How One Ancient Language Went Global,” begins with a paternal sky god. Sanskrit speakers worshipped Dyaus Pitr, or Sky Father. In Greek myth, Zeus Pater ruled the gods. North of the Alps, Proto-Italic speakers likely revered Djous Pater. Among the tribes that settled near Rome, this name became the Latin Jupiter. With further analogues in Scythian, Latvian, and Hittite, many researchers now think that the early Indo-Europeans prayed to a sky father known as something like Dyeus Puhter.

Spinney brings in other elements of Indo-European mythology, though the most comprehensive treatment in English is still M. L. West’s “Indo-European Poetry and Myth” (2007). German readers, meanwhile, can turn to the new “Indogermanische Religion,” by Norbert Oettinger and Peter Jackson Rova. Both works build on a method championed by Calvert Watkins, whose “How to Kill a Dragon: Aspects of Indo-European Poetics” (1995) set the standard for the field.

Watkins himself was something of a mythic figure. Casaubonian in his learning and drive but without the tragic vanity, he was born in Pittsburgh in 1933 and raised in New York, inheriting from his Texan parents a pride in the Lone Star State, along with a lingering twang. He arrived at Harvard with the class of 1954, and then stayed, first for his Ph.D., and then as a faculty member in linguistics and classics until his retirement, in 2003. His intellectual range was prodigious. By fifteen, he was immersed in Indo-European studies; his knack for languages was so uncanny that people joked he could board a train at one end of a country and disembark at the other fluent in its national tongue. He forgot nothing, and his eye for hidden connections bordered on supernatural. In 1984, reading a fragmentary Luwian text—a cousin to Hittite—he picked out the phrase “steep Wilusa,” a twin to the Greek “lofty Troy [Ilios],” and speculated that it pointed to an epic tradition about Troy that predated Homer. The discovery landed on the front page of the Times.