User blog comment:PhoenixRising101/Origin of Beginnings/@comment-3119203-20120322150846

Few theories.....

1) They stumbled upon them rather accidentally (example:Luffy). After seeing how strong their fruits are, these people thought that they could make something out of it, and became a pirate/Marine/etc.

2) They searched for them (example:Blackbeard). They may do this in order to join an elite organization or become a pirate.

3) They were given them for their job (example:Kaku). I think that this option is more likely for the Marines, as they may see a person with potential and give him or her a fruit on order to boost their strength or groom them for a higher-ranked position.

Or they are used as the subject of an experiment or something (example:Hancock) but this may fall under the third category.