If you were to ask when Jews started keeping the Torah, the traditional answer would be more than 3,300 years ago following the revelation at Mount Sinai, which we will commemorate in a few weeks at Shavuot.

This rabbinic chronology, however, is not generally accepted in the university world, which regards the Torah as a composite work compiled over many centuries, though debate remains over when the Five Books of Moses first appeared.

Now a new book by an Israeli scholar, Yonatan Adler, argues that Judaism as we know it might be younger than is often thought.

His starting-point in The Origins of Judaism is not when the Torah might have been written but when its laws might have been widely adopted by the ordinary people of Judea. He takes a number of practices, including the dietary laws, immersion to remove ritual purity, Shabbat and Pesach observance, and looks for evidence that they were part of what he calls “the lived experience” of people at the time.

He examines references to religious practice in a range of sources — the historian Josephus, the philosopher Philo, the New Testament, the Dead Sea Scrolls and apocryphal works such as Jubilees.

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The tomb of King Herod the Great near Bethlehem (Getty Images)

He also sifts through the archaeological record — inscriptions, papyrus fragments, food remains, coins, figurines and other remnants of antiquity uncovered by excavation of Judean sites. For example, the significant number of pools found at Herod’s palaces and other places points to the widespread practice of ritual immersion in the 1st century BCE.

Another pointer to the concern for purity is that the Judeans, uniquely in the south Levant, manufactured tableware and vessels from chalk.

Being porous and dusty, chalk was not the most obvious material to use for such purposes but, as Adler observes, stone had the advantage of being considered resistant to ritual contamination (unlike iron, leather or clay).

But he is sceptical of claims of popular knowledge of the Torah earlier than the Hellenistic period. “The earliest surviving evidence for a widely practised Judean way of life governed by the Torah never predates the 2nd century BCE,” he says.

Some customs and traditions may have been passed down the generations from the Iron Age, he believes, such as circumcision or abstention from eating the gid hanasheh, the thigh sinew (which the Torah attributes to the injury suffered by Jacob in his wrestling match with the angel). But the Torah itself may have been known by only a small circle of intellectuals, while the common folk largely remained ignorant.

According to the Bible’s own account, the people did not always follow the Torah. Not only does it tell of various episodes of prophets and some of the more righteous kings battling against the priests of Ba’al and other deities, but there are also lengthy periods of religious amnesia.

King Hezekiah of Judea oversees a national commemoration of Pesach, which had been “rarely kept” as prescribed, according to the Second Book of Chronicles: not since the days of Solomon was such an observance seen.

Later on, King Josiah has to reinstate the Covenant, and along with it the celebration of Pesach, which is kept in a way not witnessed since the days of Samuel (says Chronicles).

Many years later, Ezra reintroduces the exiles from Babylon to the Torah by instituting a public reading in Jerusalem, inspiring them to remember Succot and build their booths (according to the Book of Nehemiah).

For Adler, these stories are not evidence that the Torah was the established law of the land and that there were periods of backsliding before a religious hero was able to restore its observance. Instead, they represent “idealised portraits” by authors who “wished that their own contemporaries — who may well have also lived their lives merrily unaware of their Mosaic laws at hand — would themselves discover these laws and put them into practice”.

To support his contention that the early Judeans knew little of Mosaic law, he musters various archaeological evidence, such as the analysis of food remains, which indicate that non-kosher fish, particularly catfish, were “being consumed regularly by Judeans throughout the first half of the first millennium BCE”.

Prior to the middle of the 2nd century BCE, “there is simply no reliable evidence that the notion of certain activities being forbidden on the Sabbath was widely observed — or even commonly known of — among the Judean masses”.

Among the correspondence found at the Judean colony in Elephantine Island on the Nile is a reference to a shipment of goods being delivered on the Sabbath. (Intriguingly, one letter dated to the 5th century refers to Pischa — Pesach — and another to a seven-day festival over the same dates set for Passover in the Torah).

By contrast, there is much clearer evidence for Shabbat observance by the time of the Maccabean revolt in the 2nd century BCE.

According to the First Book of Maccabeans, after a group of Jewish rebels die rather than fight on Shabbat, Mattathias rules that in future self-defence is permissible on the day of rest.

While some scholars date the emergence of the Torah as a recognised code to the Persian period (from the 6th century BCE), Adler says “no evidence has survived… that necessarily indicates familiarity with Torah observance, while copious evidence has survived that reveals non-compliance with Torah laws”.

He finds it plausible that the Torah could have come to be established during the early Hellenistic period, following Alexander the Great’s conquests in the Middle East.

But he also makes the case for a later date during the Hasmonean rebellion against the rule of the Hellenistic Seleucids in Judea in 167-163 BCE. Judaism was “the powerful, ideological glue that would have sustained the fledgling Hasmonean state as a unified body”.

If his theory could ever be conclusively proved, Chanukah would be an even more significant festival than we appreciate.

‘The Origins of Judaism: an Archaeological, Historical Reappraisal’ by Yonatan Adler is published by Yale University Press at £50