Southshore -- the best way to understand it is that blood/marriage is historically one of the big factors in someone's candidacy for membership, though the relative should ideally also be seen as a viable candidate. Not necessarily because he's a supercriminal, but because he offers something to the organization. Of course relatives are also made just for being relatives sometimes and can cause resentment.
Funny enough, Gravano said he pushed for Charlie Aurello to be made because he was Toddo's son and didn't want him to feel humiliated. DiLeonardo has said Charlie was a man's man and respected by everyone so obviously a non-issue, but relation played a big role according to Sammy.
Something to remember about Gambino -- a boss (and every member) is supposed to put the organization before themselves. If Carlo Gambino felt it was to the organization's benefit to keep the books closed, he wasn't going to push to open the books just so his son could become a member.
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Remembered this quote from pentito Leonardo Messina:
"I represent the seventh generation belonging to Cosa Nostra. I was affiliated not because I was a robber or because I was able to kill, but because I was bound to become a member by family tradition."
- Doesn't mean the San Cataldo Family only initiated relatives, but Messina attributes bloodline (7 generations) as the most important factor in his induction. In contrast, we have Buscetta who had no bloodlines in Palermo.
- Detroit informant who stresses blood relation is the biggest factor in membership/influence and also stresses that compaesani factionalism and its politics are extremely important even in 1960s Detroit. Info on the membership supports this. Might not have been true for every Family by the 1960s, but this is the model that helped form the mafia in the US.
- From an FBI summary after interviewing Joe Valachi and other early informants. Emphasizes the class element -- we know Allegra's friend in Alcamo was a lawyer who was arranged by his bosses to marry the daughter of the San Giuseppe boss who was also a lawyer. Countless examples of high-ranking members and their children intermarrying, again an example of class-based mafia marriage.
- The "formal election" part is weird, but the FBI was able to deduce the importance of blood ties in the small Dallas Family. We know most of the members came from multi-generation Families and some were related to members in other cities.
- Freddy Santantonio gave many reasons why someone could made but as above said being a relative could fast track someone and didn't require as much scrutiny as other methods.
- Member informant who says criminal activity isn't a requirement for membership or rank but that most members are inevitably involved in something illegal. My own research has led me to believe blood/marital relation is the biggest factor for non-criminal members. Vinny Asaro said Antonino Bonventre was made despite being a non-criminal because of this.