Jurassic Park is a clashing of past and present. This motif is a constant presence in the novel, and it is this very collision of opposites that leads Hammond’s dream to ruin. He and his team of researchers have cloned extinct animals from tens of millions of years in the past \and fail to realize that dinosaurs do not live on the modern earth for many reasons. First, they cannot thrive in an environment with a much lower oxygen content in the air. Second, they are prone to diseases of the present which did not exist in their time. Third, dinosaurs are a completely foreign type of animal which humans cannot hope to comprehend. Grant realizes that, in a twist of irony concerning an old debate, dinosaurs are neither lizards nor birds; instead, they are entirely their own. All of these problems prove to be true as dinosaurs regularly fall ill with strange symptoms and die, and perhaps more importantly, the dinosaurs do not interact well with humans. From the moment that the power is out, the dinosaurs begin wreaking havoc on the park and its occupants, including each other. People are eaten, injured, and traumatized by the horrors they witness.