WMG: After Earth
Earth's animals were never evolved to kill humansFirst of all, that's completely ridiculous. Second, the animals don't even act that way during the movie. Third, it's possible that over time, during humanity's stay on that other new planet, Earth's inhospitable nature and the circumstances of mankind's subsequent migration to space were exaggerated either by people who wanted an exciting story or people who wanted Mother Nature to seem like the bad guy. Now, everyone just thinks that everything on Earth has no desires beyond extinction of humanity, when they're really just... acting like ordinary animals.
Rangers were genetically engineered from Autistics.The difficulty they had expressing emotion caused me to think of this. It was mentioned that the Rangers were originally leading humanity in its exodus from Earth before the Ursas came. At this time they weren't warriors, they were just leaders. They'd been created when humans realized that it was their inability to put aside their emotions that had caused the destruction of Earth (ie thinking in the short-term, and looking for gratification over sustainability), so they had to create a new breed of humans who could put their emotions to the side. Now, Autistics today aren't really like this, but the genes that make them more socially awkward are still (in this movie's verse) usable to make people who are just generally less emotional. When the Ursas attack, they're able to use this to wildly decrease their fear responses, and eventually to Ghost.
- Autistics have trouble with facial expressions, not pheromones. And we feel the basic emotions, fear, rage, sorrow, happiness, at the same strength as neurotypicals, if not more. It's complex emotions like jealousy that we have trouble with. In addition there is a phenomenon known as the autistic meltdown that might be problematic for the Rangers.
- It's more likely they came from schizoid personality disorder, which features a flat emotional range due to withdrawing into the mind and blocking out other relationships.
- That could explain the way the plants moved when it's about to become cold.
It's not Earth.It was just a bad terraforming attempt, or one the aliens made go sour. But the point is they're mistaken about that particular planet being Earth.
Earth's animals were genetically-engineered as part of the environmental cataclysm.The film doesn't really give specifics on how the Earth came to be uninhabitable, so for all we know, mass genetic engineering could have played a part in Earth's downfall, which would explain how quickly and radically Earth's biosphere evolved.