In recent polling, about half of the Israeli population (but not the Orthodox) advocated allowing Jewish identity to follow either parent. This contrasts with the traditional definition whereby Jewish descent depends on the mother. In early biblical times the criterion was beit av, "the father's house" (Exodus 1:1, Numbers 3:2), but this was superseded by the matrilineal principle, derived from a midrash halacha on Deuteronomy 7:3-4 which refers to "your son" as the child of an Israelite mother - a rule accepted by all halachic authorities (Kiddushin 65b/68b, Yad Issurei Bi'ah 15:4, Shulhan Aruch E.H. 8:5). The change was not unexpected, since the Bible already spoke of not only a father's but a mother's house: In Exodus 1:21, God rewards women's piety by "making them houses," and Ruth 4:11 states that Rachel and Leah "built the house of Israel." It could be that there was an early stage of fluidity, but when the exiles returned from Babylon they saw the influence of "foreign wives" and encouraged Ezra (10:2-4, 9:11) to make rulings against outmarriage and the easy acceptance of "the daughters of strange gods." Ezra claimed to be following prophetic teaching, though the sages did not list the negative status of gentile wives among Ezra's or the prophets' enactments. George Foot Moore in his Judaism in the First Centuries of the Christian Era (1927, vol. 1, page 20) finds a parallel in Greek history at the same time as Ezra, when Pericles restricted Athenian citizenship to the child of an Athenian man and an Athenian woman. We do not know whether Ezra saw this as a precedent, but he must have been aware of it. Solomon Zeitlin (Jewish Quarterly Review 51:2, 1960, pages 135-140) thinks the ruling is a response to the provocative action of Sanballat in marrying his daughter to a son of the Jewish high priest. According to Zeitlin, Judaism had to block the child of a non-Jewess from being a Jew or a priest. Matrilineality took time to become entrenched, but by the time of the Mishna (Kiddushin 3:12) it was accepted that a child follows its mother's status, and the sages interpreted Jacob's blessing, "The Lord make you as Ephraim and Manasseh" (Genesis 49:20) to aver that the boys' mother was not a gentile but the daughter of Dinah, sister of Joseph. In the Roman period there were so many conversions and semi-conversions to Judaism that there needed to be a clear definition of Jewish status; otherwise, according to Lawrence Schiffman (Who Was a Jew?, 1985, ch. 2), Judaism would have been swamped by the children of gentile Christian mothers. Rabbinic Judaism is unyielding in maintaining matrilineality. Lord Jakobovits (The Timely and the Timeless, 1977, pages 198-217) says the certainty of maternity must be set against the possible doubt of paternity. Even in nature the mother's bond with the child is firmer than the father's. And the mother has the superior influence on the child's religious development. So matrilineality is here to stay. The writer is emeritus rabbi of the Great Synagogue in Sydney, Australia.