There's a fellow in Israel who was born a Muslim Arab in Hebron, and eventually crossed the lines to become an orthodox and very right-wing Jew. There's another one whose great grandfather founded the Red Army and called himself Trotsky, and the descendant is also a far-right hothead (he used to live in Hebron, but I've lost track of him).
People have free wills, and this can lead them to some of the most peculiar places, irrespective of where they started.
But most often, it doesn't. Statistically most people more or less end up being what you'd have thought. When they don't, it's often because history intervened. The Postwar Germans don't resemble the society of their parents and grandparents; the fact so many of them do resemble each other in not resembling their gradparents, is no coincidence. Most people don't deviate all that much.
The Forward has published another rumination on the declining number of American Jews. The thesis: the Orthodox are multiplying, all the rest aren't, not at all. Surprise!
I've taken a wee bit of flak by some commenters as I've touched upon this topic in recent weeks. So here's an attempt to clarify.
Many Christian denominations have it pretty simple in the identity department. If you believe the right things, you're in; if not, you're probably out. Belonging to the right community - as in, going to the right church - is also helpful.
It's different these days with Jews. The belief part of it was never particularly important; the belonging was simple when everybody did it but then got more complicated. Roughly speaking, I'd say there are four ways to tell who's a Jew.
1. By what the antisemites say.
2. The Halachic way (traditional Jewish law). If your mother is Jewish, so are you. Interestingly, this works for children, perhaps for maternal grandchildren, but not for great grandchildren. If your mother and grandmother were not Jewish enough to marry Jewish men, the rabbis probably won't easily recognize you, either.
3. The religious way. This means living a life in which Jewish ritual plays an important and consistent role. I'm being careful, please note, and not saying it has to be orthodox ritual, though any empiric measure I can think of would indicate that orthodox ritual has greater staying power than the other forms, at least statistically. But if your form of non-orthodox ritual keeps you firmly in the fold, most other Jews won't doubt you (the Orthodox, however, will want to be certain your mother was Jewish before they marry you).
4. The cultural way. This is where I've been censured a bit, so I'll be clear about what this means. Being Jewish has always been a significant componant of an individual Jew's identity. For the past 200 years or so, it has been possible - at least theoritically - for being Jewish to be central even while not being religious. Or at any rate, it has repeatedly been tried.
The anecdotal evidence in the column cited above is yet another illustration of the probability that the cultural way works for a generation or two, but not much longer. Jews lucky enough to live in lands where the antisemites don't care (because they're gone, or because they fixiate on Israelis, not local Jews), who see no problem with marrying non-Jews, and who aren't religious, won't have Jewish grandchildren. Except in Israel.
Israel is the one place where being culturally Jewish may be statistically feasable. The language spoken by the Israelis is the Jewish language, the public holidays are the Jewish holidays, and the war with the neighbors has significant elements of rejection of things Jewish, so it fits the first catagory. Not to mention that most marriages will be between Jews, obviously.
So yes, I'm saying clearly what some of you have taken exception to: if you want to stay Jewish abroad your best bet is to be orthodox. If you don't want to think about being Jewish overmuchly while remaining strongly Jewish, you need to be in Israel.