This film takes place in the same universe as The Flintstones, but centuries earlier.There are no man-made cities, domesticated or enslaved animals, or advanced culture when this movie begins. All cavemen live like... actual cavemen, with just a cave to live in, no inventions, and simple animal hides for clothing. When Guy comes with an evolved brain and tons of inventions, he inspires the Croods to adopt some of that too, and at the end, they become the first explorers in human history. Guy leads them in finding more Cro Magnums and other cavemen in other regions. Eventually their descendants start Bedrock, and their culture gradually develops. Of course, this begs the question of why dinosaurs exist in Bedrock, and they do not in The Croods.
This movie is more proof that The Flintstones takes place in the post-apocalyptic future of The Jetsons.The supposed Cro-Magnons were actually just the first people to re-discover the Lost Technology and start rebuilding human society, as well as reintroduce and redomesticate the Jurassic Park-style clones of dinosaurs and other prehistoric animals (although some cloned sabertooth cats and other Pleistocine animals obviously escaped and interacted with the Croods and their compatriots). The Croods and their kinfolk probably just lived in a different part of the world and the proto-Flintstones merely acted as technological "missionaries". Alternatively, 'The Croods could take place after The Flintstones. The Bedrockites were rebuilding human society in chronological order; hence why characters in The Flintstones acted like 1960's Americans while the Crood family acted like people of The New Tens ("shell phones" and all).
Eep and Guy are Cro's ParentsFor those not in the know, Cro is an animated science show from the early 90's. Orphaned Cro-Magnon is adopted by Neanderthals whose patriarch is against new ideas.This could refer to either. And Cro has red hair, is exceptionally smart, and doesn't bat an eye at highly intelligent creatures.
The story isn't set on Earth at all.The vast majority of the film's flora and fauna are far, far too different to have ever existed on our own Earth. Rather, the characters are descendants of a failed space colony on an alien world. The Croods' ancestors were future Super Soldiers, genetically engineered to be strong, fast, and fierce, while Guy is descended from unmodified humans. These two branches of humanity went their separate ways after the colony failed, and the Super Soldiers forgot even more of their former technology than their unmodified counterparts. Only their shared language and a few rudimentary concepts (e.g. that stars are suns) survived the passage of generations.
The Croods and Guy are different species of human.The vast majority of the Croods strongly resemble Homo neanderthalis, while Guy is almost certainly Homo sapiens given his appearance and behaviour. Since the two existed at the same time and could interbreed, it's not impossible. In addition, Ugga is half-sapiens - she looks a lot less Neanderthal than Grug or Nanna, while Sandy and Eep look slightly sapiens.
Guy is a time traveller from the future.He seems to know much more than the Croods, and even though the majority of that must be because he's actually been outside a cave in his life, there are just some things that don't make sense, like knowing the names of several things that just didn't exist yet or couldn't be named yet.
This film is set not in the past, but actually in the distant future.Look at the animals in this film. There is no possible way this could have taken place in the past. This is clearly a post-apocalyptic future where humans have become an endangered species. (Kind of like After Man: A Zoology of the Future, or The Future Is Wild.)
The Croods themselves are possibly regular humans who reverted back to a caveman-like state. Most of them have an instinctive fear of anything "new", due to subconscious memories of how humans have junked up the earth in the past. Guy is one of the last remaining "regular" humans.
Every single creature in this evolved from a modern-day animal.