Earlier in this book, I stated my belief that family filled the role of religion in the Shire. Hobbits' exhaustive study of family histories, and of exactly how one person is related to another, has the importance of religion; it's not simply an "interest," but affects how everyday life is lived. The intricacies of birthday observations as described in letter #214 demanded that a Shire resident know not only his or her blood relationship with the celebrant but the exact distance between their residences; simply keeping track of the birthdates of relatives who were due gifts would have been a task requiring religious attention (literally), made only slightly easier by the very orderly Shire calendar. It's also interesting that Shirefolk noticed those who did only the minimum required by the rules; a "twelve-mile cousin," who gives presents only to those he or she absolutely has to, sounds a lot like a Sunday Catholic. Of course, Tolkien wrote letter #214 after LotR was published - in response to a reader's question, in fact - but it fits perfectly with all we learn about hobbits in his published fiction.
Throughout that fiction, careful reading can pick up some implicit customs, such as how the relationship between two people affects the way they address each other (hint: watch for how the word "cousin" is - and isn't - used as a title). During "Three Is Company," Frodo can roll Pippin out of his blankets and make decisions about what path to take because he ranks above Pippin in regard to family relationships; Pippin may be the son of the Thain, but Frodo's a cousin who's a generation above him. Pippin can disagree, but he doesn't rebel, and the relationship is so well understood that Frodo never has to explicitly "pull rank." Frodo's also a generation above Merry; he wisely shares some decision-making with Merry while the group is in territory that Merry's more familiar with, and the dynamics of that are interesting to watch in themselves. Merry acts as guide in the Old Forest, but it's Frodo who decides to go there.
A will needing to be signed by seven witnesses (in red ink) goes beyond the need to prove that the signature is authentic. The number of people who would have needed to gather at one place and time to witness the signing indicates that it was considered the business of the broader community, which makes perfect sense since a will had the power to override the blood relationships that would normally determine a person's heir - no small matter in a society where those relationships were so fundamental. Tolkien's offhand remark in letter #214 that adoptions were "rare" in the Shire also makes perfect sense; because of extended families, orphans would very rarely be left with no one to care for them, but for someone to legally change a relationship so that it no longer agreed with physical lineage, as Bilbo did with Frodo, would be extraordinary. No wonder Lotho demanded to see the will! (Frodo's designation of Sam as his heir goes beyond extraordinary, but since Sam was of legal age at the time it didn't involve adoption.)
All of the above is simply to emphasize the importance of biological family relationships in the Shire. It was a strong group society, with a person's identity linked to his or her place in the family. If family structure is the "state religion" of the Shire, Bilbo and Frodo may not be heretics, but they're not completely orthodox.
Both of them came from family situations that set them apart from the way things normally worked in their society. Bilbo's parents died at relatively young ages for hobbits, and he was an only child, so was left to take over as head of the Baggins family and as the Mr. Baggins of Bag End as a young adult. Frodo was orphaned at the same age JRRT himself was, although more suddenly. We aren't told the circumstances that led to Frodo remaining at Brandy Hall: whether he just "fell into" the situation because that's where he was when his parents died, or whether it was a family decision. Either way, as a Baggins he wouldn't have had a well-defined place in the Brandybuck family structure. Strong group societies operate by identifying not only who belongs to the group, but also who doesn't. In a strong group society based on biological lineage, Frodo's identity would have been somewhat ambiguous to outsiders, and possibly even to himself. Because he's still a child, Frodo doesn't simply step into his father's role as Bilbo had. It has always seemed to me that one of the most Providential occurrences in LotR is that Bilbo and Frodo were able to form the bond that they did, and become family in a way that was different from the way things were "supposed" to work in their society.
In the essay immediately preceding this one, I said that I believed Tolkien's approach to the whole idea of "strong group society" was more Catholic than English. I base this primarily on the characters who choose to be family. Besides each Catholic's ongoing choice to be part of the Church, this idea of a "family of choice" is also reflected in the existence of religious orders, in which the community the person joins is considered his or her primary family.
It can be interesting to look at changes Tolkien made to the story as it developed, as I assume most of them were decisions that had reasons behind them. Early in the process, Bilbo was married and Frodo (or, I should say, the character who became Frodo) was his biological son. As far as I can see, there was no need to change this for the sake of the plot. When he returned from his adventure with the dwarves, Bilbo was still young enough by hobbit standards that marriage would have been a definite possibility. When the Quest begins, it would have been reasonable for Gandalf to tell Bilbo that it needed to be taken on by his son, as is decided at the Council in the book. It would have been very simple to have Bilbo's wife die before the end of the story so that he and Frodo could sail West together without leaving a spouse behind; Frodo could have been either an only child or the youngest, so that Bilbo's responsibility to his children would have been finished, as it was for Sam when he followed them.
But when I think about this scenario as a possibility, I just don't like it - and I think I know why. The fact that Bilbo and Frodo choose to be father and son adds an entirely different dimension to their relationship and to the love they have for each other, especially since Frodo was old enough at the time of his adoption to have an active choice in the matter. It takes away any reason someone might have to dismiss it as "natural": "Well, of course he'd offer to take on the Quest to protect his son"; or, "Since Frodo's mother has died, naturally the person he most loves is his father." Frodo becoming Bilbo's heir is almost a first step that has to be taken before things can move even further with Frodo making Sam his heir, which not only shifts the line between family and not-family, but obliterates it.
Can I say that Tolkien made a very Catholic decision here?
I get a little nervous at times when some of my more politically conservative Catholic friends throw in their lot with the "family values" folks. Not that Catholic theology, or teaching, or mindset, or way of looking at life, or anything else, is anti-family by any means. But biological family is not the ultimate community. The nuclear family, which is often the primary concern of the family values folks, is even less central. In the United States, and in the parts of the world that are following in its weak-group footsteps, it may seem like the nuclear family is the last bastion of interpersonal support and commitment. But if that's true, we're in bigger trouble than even the family values folks think we are.
Beyond talking about the permanence of marriage and pointing out the hypocrisy of saying that someone didn't have to financially support his parents if he promised his money to the temple (and the priests), Jesus didn't talk too much about the importance of families. We might say this is because the importance of families didn't need to be talked about much at that time in history, but Jesus got more radical than that. The Gospels contain a number of statements that show the biological family in competition - or even in conflict - with the new community he was gathering around himself:
"For I have come to set a man against his father, and a daughter against her mother, and a daughter-in-law against her mother-in-law; and a man's foes will be those of his own household. He who loves father or mother more than me is not worthy of me; and he who loves son or daughter more than me is not worthy of me..."
"Who is my mother and who are my brothers?" Stretching out his hand toward his disciples, he said, "Here are my mother and my brothers!"
And the one beloved by Catholics following a vocation that leads away from a personal family life:
"...there is no one who has given up home, brothers or sisters, mother or father, children or property, for me and for the Gospel who will not receive in this present age a hundred times as many homes, brothers and sisters, mothers, children and property - and persecution besides - and in the age to come, everlasting life."
The idea of the Christian family being a "domestic church" (a concept used by both Catholics and Protestants) isn't at odds with these statements of Jesus, because it situates the family within this new community rather than in competition with it. The Church isn't a community because it contains families; the family is holy, and sacramental, because it's part of the Church.