As a complete outsider, the way I see it a lot of the systems at Facebook actually originated within Google, but were never published. Engineers from Google the

As a complete outsider, the way I see it a lot of the systems at Facebook actually originated within Google, but were never published. Engineers from Google then went to work at Facebook and wanted to replicate the systems they were already familiar with. The only difference is that Facebook actually releases most of these things as open source. So I guess the good news is that when engineers leave Facebook and go to work at "next big thing" they can bring the same tools with them without having to rewrite them again.