Humani generis unitas (Latin for On the Unity of the Human Race) was a planned encyclical of Pope Pius XI before his death on February 10, 1939, which condemned antisemitism, racism and the persecution of Jews. Because it was never promulgated, it is sometimes referred to as "The Hidden Encyclical" or "The Lost Encyclical."
In June 1938, Pius XI summoned American Jesuit John LaFarge, who began to prepare a draft of Humani Generis Unitas, which LaFarge and two other Jesuits—Gustav Gundlach and Gustave Desbuquois—worked on in Paris; the draft was approximately 100 pages long. Another Jesuit translated the draft encyclical into Latin, presenting it to Vladimir Ledochowski, then the General of the Society of Jesus—who had chosen Gundlach and Desbuquois for the project. The draft encyclical was delivered to the Vatican in September 1938.
Some secondary sources—as well as Cardinal Tisserant the Dean of the College of Cardinals—claim that Humani Generis Unitas was literally on Pius XI's desk when he died of a heart attack on February 10, 1939.
Pope Pius XII, who succeeded Pius XI, did not promulgate the encyclical. Critics of Pius XII—notably John Cornwell in his controversial work Hitler's Pope—have cited his failure to promulgate the encyclical as evidence of his alleged silence toward anti-Semitism and The Holocaust, and analysis of the encyclical figures prominently in most comparisons of the policies of Pius XII and his predecessor.
Pope Benedict XVI decreed in June, 2006 that all documents from the reign of Pius XI in the Vatican Secret Archives should be opened, and on September 18, 2006 over 30,000 documents were made available to researchers.
The first 70 paragraphs, probably authored by Gundlach, are a critique of theological modernism, unorthodox re-interpretation of Sacred Scripture, nationalism, and racism; the remaining 108, likely authored by all three Jesuits, contextualized the first part of the encyclical with the social role of Catholic educational institutions and anti-Semitism.
Although the draft encyclical clearly condemned racism and anti-Semitism, the document is deeply grounded in anti-Judaism. The draft encyclical criticizes the majority of post-Messianic Jews for not acknowledging Jesus Christ as the true Jewish Messiah.
The “encyclical” clearly condemns American racial segregation and Racism and Nazi German anti-Semitism  Racism is a denial of the unity of human society. , a denial of the human personality  and a denial of the true values of religion  There is no relation between race and religion  last not least because racism is destructive to any society  The text points out that racism is destructive not only for social relations within a society but also for international relations and relations between different races. 
The encyclical condemns the persecution of Jews as well. “These persecutions have been censured by the Holy See on more than one occasion, but especially when they have worn the mantle of Christianity".  “This unjust and pitiless campaign against the Jews has at least this advantage”, according to the “encyclical”, because the true nature, the authentic basis of the social separation of the Jews from the rest of humanity … is religious in character. …Essentially, the so-called Jewish question … is a question of religion and, since the coming of Christ, a question of Christianity.  The encyclical blames the Jews of the time of Christ for having brought their own Messiah Jesus Christ to death: "The very act by which the Jewish people put to death their Savior and King was, in the strong language of Saint Paul, the salvation of the world".  The encyclical continues by accusing Jews of blind materialism.
- Blinded by a vision of material domination and gain, the Israelites lost what they themselves had sought. A few chosen souls, among whom were the disciples and followers of Our Lord, the early Jewish Christians, and, through the centuries, a few members of the Jewish people, were an exception to this general rule. By their acceptance of Christ's teaching and their incorporation into His Church, they shared in the inheritance of His glory, but they remained and still remain an exception. "What Israel was seeking after, that it has not obtained; but the chosen have obtained it, and the rest have been blinded" (Romans 11:7).  The encyclical argues, that
- By a mysterious Providence of God, this unhappy people, destroyers of their own nation, whose misguided leaders had called down upon their own heads a Divine malediction, doomed, as it were, to perpetually wander over the face of the earth, were nonetheless never allowed to perish, but have been preserved through the ages into our own time. No natural reason appears to be forthcoming to explain this age-long persistence, this indestructible coherence of the Jewish people.
Reaction of Pope Pius XII
Pope Pius XII, who according to the authors, was not aware of the text before the death of his predecessor,  chose not to publish this encyclical. However, his first encyclical Summi Pontificatus (October 12, 1939), published after the beginning of WWII, has the identical title On the Unity of Human Society and uses many of the arguments of the text, avoiding most of the negative characterisation of the Jewish people and rabbinic religion still contained in the text of the original encyclical, planned and written before the invasion of Poland and the start of the Second World War.
Summi Pontificatus sees Christianity being universalized and opposed to every form of racial hostility and against racial superiority. There are no real racial differences, because the human race forms a unity, because "one ancestor [God] made all nations to inhabit the whole earth".
- What a wonderful vision, which makes us contemplate the human race in the unity of its origin in God. . . in the unity of its nature, composed equally in all men of a material body and a spiritual soul; in the unity of its immediate end and its mission in the world; in the unity of its dwelling, the earth, whose benefits all men, by right of nature, may use to sustain and develop life; in the unity of its supernatural end: God himself, to whom all ought to tend; in the unity of the means for attaining this end;. . . in the unity of the redemption wrought by Christ for all.
- Georges Passelecq and Bernard Suchecky, L’Encyclique Cachee de Pie XI, Une occasion manqué de l’Eglise face a l’antisemitisme , Editions La Decouverte, Paris 1995, (engl)The Hidden Encyclical of Pius XI (Harcourt, Brace, and Co., 1997).
- Encyclical Summi Pontificatus on the Vatican website
- ↑ 1.0 1.1 1.2 1.3 1.4 Richard G. Bailey. August 2001. "The Hidden Encyclical of Pius XI." Canadian Journal of History.
- ↑ 2.0 2.1 2.2 George Sim Johnston. 1999, October 8. "Pius XI's "Hidden Encyclical" on Anti-Semitism: An Appraisal."
- ↑ 3.0 3.1 The Holocaust Chronicle. 2002. "1937: Quiet before the Storm." p. 112.
- ↑ 4.0 4.1 Frank J. Coppa. 1998, September 22. "Pope Pius XI's "encyclical" Humani Generis Unitas against racism and anti-Semitism and the "silence" of Pope Pius XII." Journal of Church and State.
- ↑ Passelecq and Suchecky, p. 151.
- ↑ Zenit News Agency. 2006, July 2. "Benedict XVI Opens Archives on Pius XI."
- ↑ Frances D'Emilio. 2006, October 13. "Newly opened files helping historians to understand priorities of future wartime pope, Pius XII." Associated Press.
- ↑ (Humani generis unitas 135
- ↑ without explicitly naming these countries.
- ↑ Humani generis unitas 112
- ↑ (Humani generis unitas 113 seq.)
- ↑ Humani Generis Unitas 116 seq.
- ↑ Humani generis unitas 120
- ↑ Humani generis unitas 123
- ↑ Humani generis unitas 130
- ↑ Humani generis unitas 131
- ↑ Humani generis unitas 133
- ↑ Humani generis unitas 135
- ↑ Saint Paul adds: "But by their offense," that is, through the Jews' rejection of the Messiah, "salvation has come to the Gentiles" (Romans 11:11).Humani generis unitas 136
- ↑ Humani generis unitas 136
- ↑ Letter of Father Maher to Father La Farge, March 16, 1939
- ↑ Summi Pontificatus
- ↑ Pius XII, Enc. Summi Pontificatus 3;
- ↑ Pius XII, Enc. Summi Pontificatus 3;
- Humani Generis Unitas draft of a section as of 1938
- Pius XI and the mystery of the disapperead encyclical (YouTube video, original Italian, with English subtitles, duration 04:38)la:Humani generis unitassl:Humani Generis Unitas