The pictures that everyone is so fascinated by represent only a tiny fraction of what's there. Most of it is simply lines, like the ones pictured above with the rocks cleared. They crisscross everywhere, they're very straight but no particular pattern is apparent - from the air, or elevated ground, they look similar to the lines on a cutting board. No apparent pattern. Most of them are not very wide, again, the pictures with the rocky ground are typical of the vast majority of the lines.
I have a hard time imagining these are fake - what would be the point of creating thousands of highly uninteresting paths in the desert that, for the most part, no one will even look at? My guess is that these lines are real, but mundane. They're maybe for ritual processions or they followed some stars (Peruvian civilizations were obsessed with astronomy so as to time the planting and harvest correctly) or just some relatively mundane thing we can't guess at.
What I think happened is that someone decided to add the animals etc, as well as the "landing strip" bits, some time in the early 20th century. I think they may have seen the lines as reminiscent of Martian canals (a popular idea at the time, inspiring such novels as the John Carter books) and decided to improve upon them. I think it was most likely a Brit or American familiar with things like the Uffington White Horse or the Cerne Abbas Giant (itself a fake).
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