If it evolved over several generations then there would be immediate precursors to Christianity in the region that contained many, but not all, of the same characteristics.

There aren't. I don't really like giving straight out negative answers because it doesn't read well when there's no evidence, but there is no evidence of a Christian-like precursor to Christianity. There are some precursors to elements of early Christianity found in Judaic religious texts of the time, but not the kind of thing that you are suggesting, "a known religion that existed very close in geography, philosophy".

The reason why is that Christianity is built upon a messianic interpretation of the Hebrew Scripture and the identification of that Messianic figure. Any other Messianic type religion would also have to found itself upon its identification of the Messiah. Christianity in its nascent form can't really exist until it has its Messiah figure.

Secondly, I would argue, that Christianity does something unprecedented in the way it develops early binitarian and trinitarian patterns of understand Jesus as God within, and then beyond, strict 1st century Judaic monotheism. There are few to none parallels for this kind of inclusion of a 'second figure' on the God-side of the equation. Larry Hurtado's work in this area is very strong, on my reading.

slightly before the general ~0AD birth date of Jesus?

Minor point: There was no Year Zero in the AD/BC year-counting system. Jesus was nominally born in Anno Domini 1 ("The Year Of Our Lord" 1). The year preceding that was the first year Before Christ: 1 BC.

Allow me to turn your question upside down. It will answer it best, IMO.

When were Christians, Christians (and Jews, Jews for that matter)? Depending on what you mean by the term, we could be talking about more than 100, perhaps 200 years after year 1. We often like to think of these religions as branches on a rather thick trunk we call monolithic Judaism; however, that is a gross oversimplification. A better analogy would we the interaction between a few stones thrown into a lake and the interaction between the waves that come thereafter. The thought world, philosophy, cosmology, Scripture, even beliefs about the/a Messiah(s) of the groups that would later be Jews and Christians are not discrete. Of course, if we simply define Christians solely by Jesus being the central figure, then your question doesn't make sense.

Question: For stuff like this where the answer I believe is no, how can you cite evidence to support your claim?

The precursor to Christianity is Judaism.

The Book of Isaiah more or less describes a Jesus-like messianic figure and is still featured prominently by modern Christians. The Book of Daniel has an apocalyptic bent and describes the sorts of rewards for the righteous and punishments for the unrighteous that would be featured in Jesus' teachings and expanded on in later Christian doctrine (the unrighteous are tossed in a fire, IIRC). Similar messianic and/or apocalyptic teachings are found in other books, and Jesus-like figures were more or less compatible with Judaism of the time (ignoring the resurrection and divinity doctrines).

I can't answer your question directly, others have, but to understand how Christianity came about it's probably important to note that Christianity did evolve, and the characteristics you refer to took several hundreds of years to evolve after Christ. Even the Scholastic Christianity of the medieval period would appear very different to the Christianity of today. In this sense, the "immediate precursors to Christianity" are the earlier forms of Christianity; the earliest Christianity didn't have many distinguishing features to set it apart from Judaism, these all came with time.