For instance, in Japan, it is a function of parentage. If your parents are Japanese, you are Japanese. If your parents are not Japanese, then you are not Japanese, even if you are born in Japan. But what if you are born in Japan, but your parents are not known, nor their status?
If both parents are unknown and the child was born in Japan, then the law says that the child is a Japanese citizen. This case has probably not been tested recently in the courts or otherwise, so the status of such a child will probably in reality, be stateless.
I bet if the child in such a case was clearly Japanese in physical appearance, he or she would be given citizenship. If not, he or she would be stateless.
These laws are the norm in most other countries where nationhood and cultural heritage overlap almost perfectly. Even though it is technically possible for a white person or a black person to become a Japanese citizen, the laws mean that virtually all Japanese citizens are, well, Japanese.
Hence this reaction:
More than 1,000 Japanese rallied in Tokyo yesterday to oppose allowing women and their children to inherit Japan's Chrysanthemum throne. Prime Minister Junichiro Koizumi has promised to submit a bill to parliament by June that would put four-year-old Princess Aiko in line to ascend the Chrysanthemum Throne and enable her first child to succeed her. "Did the panel consider if Princess Aiko married a man with blue eyes after falling in love when studying abroad and the possibility that their first child would become emperor?" Takeo Hiranuma, a former economy and industry minister, told the rally. "This has to be prevented by any means." However, opinion polls show overwhelming support for letting Aiko rule.
An Emperor with blue eyes? Impure blood? Japan would fall apart!
If you aren't Japanese, you could be forgiven for feeling a bit insulted.
Hiranuma is not a bigot, as such, but is voicing a concern that we would find difficult to understand. For us, citizenship is a legal construct, not a genetic one. But remember too that even in Canada, this attitude has not always been universally applied. For many years, Chinese people could not become Canadian citizens, and up until 1923, they were subject to a head-tax by immigration authorities. Those throwbacks to a genetic component to citizenship are gone now, and good riddance. But while in Canada those sorts of regulations were inconsistent with the legal principles even when they were enforced, in places like Japan, the correlation between citizenship and your bloodline makes perfect sense. It therefore makes sense that the law should reflect that correlation.
Any change to the law that weakens that connection is going to cause a lot of consternation.
We've been working on this since the country was formed in 1867, and even before that. Despite this, Canada still has problems with bigotry, and probably always will. We should be thankful that we've had so long to deal with this. In most places, like Japan, they have no experience whatsoever with what it means for a fellow citizen to be different. That's too bad for them, because I've always thought that accepting differences, and ultimately ignoring them, was one of our greatest strengths.