Oh, God ! Not another argument on this old chestnut of a topic. Let's give it a miss. But aside from the arbiters of Jewishness in charge of emigration to Israel, a view could be that if you live like a Jew, if you feel that you are Jewish, if you have the genes of definite Jewish people, you can be a Jew. How many Jews live without any connection to the religion, to "Jewish culture" (a widely diverse idea in any case) or have given even much thought to the fact? Yet, nobody challenges them because they happen to have "right genes". Sometimes they have nothing more than a certain history. Ariel Segal writes of a small community in the isolated jungle city of Iquitos in far eastern Peru. They are descended from Jewish men who arrived from Morocco and Europe in the late 19th-early 20th century to profit from trade during the rubber boom. Most of them married local women or at least had children by them. These children mostly never got any religious instruction. There was no synagogue, no rabbi, nowhere to learn about anything Jewish, yet they felt themselves a community. An "imagined community" in Benedict Anderson's terms, and they tried to do something about it, tried to integrate with the stronger Jewish community in Lima when communication became easier with the introduction of air service. Some even tried to emigrate to Israel. Neither of these efforts was marked by much success. Many of them attended Catholic services, celebrated Christmas and other Christian holidays and held beliefs that mirrored the Amazonian Indian world around them at the same time that they claimed to be Jewish.. If we use the word "syncretism", it would not be inaccurate. Yet, I ask you, aren't all religions in the world syncretic? It is just a matter of how long the syncretism has gone on !! You can read another such interesting story, involving Jews, in Steven Kaplan's book on the Beta Israel of Ethiopia.
If you ask me, (you didn't) Ariel Segal must be a hell of a nice guy, somebody whose honesty you would respect. Maybe he indulged in even too much honesty by including bits from his personal diary in a book which hangs between History and Anthopology. But he does what few researchers ever do---put his own feelings and personal involvement with his "subjects" in view. I appreciated that a lot. Maybe he repeated some information and ideas more often than necessary, but if you finish this book, which is not hard to do, you will have a very good picture of this small, interesting community produced by a forgotten history. Some parts, particularly in the beginning, seem to have been translated from Spanish in, shall we say, less than expert style. That's a small criticism of an otherwise good book.