User blog comment:Kaido King of the Beasts/Chapter 840: My Worthless Son/@comment-24.236.172.91-20160921235713/@comment-24850639-20160922164846

Interesting point. I'm not quite sure how far Oda plans on diving in to the Sci-Fi world, but this chapter definitely set all this up as a matter of science. In science, when experimenting something, its very common to have a "control" - a subject that remains constant as a means of comparison to other subjects that are receiving whatever is being tested. It is VERY interesting that they chose to number her Zero, rather than starting at 1 with the oldest. Add to that the fact that she's the only one of them with normal eyebrows, and I definitely think you're onto something. She was probably still modified for sure, but I'm guessing to a somewhat different extent than her brothers.