Jews no longer constitute a majority in the land between the Jordan River and the Mediterranean Sea, according to an expert on Jewish demographics.

Prof. Sergio DellaPergola of the Hebrew University told The Jerusalem Post on Thursday that Jews – as defined by the government – now number less than half of the total population in Israel, the West Bank and the Gaza Strip.

"If people ask when Jews will lose their majority, then it’s already happened,” DellaPergola said. “If one combines the Palestinian population of the Gaza Strip and West Bank, includes foreign workers and refugees, whose numbers have grown rapidly in recent years, and omits Israelis who made aliya under the Law of Return but are not recognized as Jews by the Interior Ministry, then Jews are slightly less than 50% of the population.”

The finding is potentially significant in the context of efforts to reach an accommodation with the Palestinians.

Former prime minister Ariel Sharon made a late-life political turnaround, unilaterally dismantling the entire Gaza Strip settlement enterprise and trending toward separation from the Palestinians in parts of the West Bank, out of a concern that, in the absence of separation, demographics could leave the Jews as a minority between the river and the sea, with implications for the Jewish nation’s sovereign capacity to determine its future. Prime Minister Binyamin Netanyahu, who last year conditionally backed Palestinian statehood, has also often cited concerns about Israel maintaining a strong Jewish majority.

The 2008 Palestinian census found 3.76 million Palestinians living in the West Bank, the Gaza Strip and east Jerusalem, up 30% from 2.89 million a decade earlier.

Within Israel, according to Central Bureau of Statistics figures issued last year, there were 5,569,200 Jews – 75.5 percent of the population.

While DellaPergola says that Jews are already a minority between the River and the Sea, some critics charge that figures for the number of Palestinians living in the West Bank are exaggerated by hundreds of thousands due to double counting of the population of east Jerusalem, who appear in both the Israeli and the Palestinian census, and by including people living abroad who possess local identification cards.

On Tuesday, DellaPergola released a report conducted on behalf of the North American Jewish Data Bank in collaboration with the Jewish Federations of North America. He estimated the number of Jews around the world at 13,428,300.

More than 80% of Jews live in two countries: Israel and the US. The Jewish state has an estimated 5,703,700 of them, whereas about 5,275,000 are in America.

DellaPergola said he had used a social categorization to estimate the number of Jews.

“I didn’t go by the Halacha,” he explained. “Instead, I used a social definition to determine the core population: Someone who identifies as Jewish and those with Jewish parents who have no other religion.”

Using a broader, ethnic definition, DellaPergola believes there may be as many as 14 million people with Jewish ancestry outside of Israel who could make aliya under the Law of Return.