We finally know! Whay are there dinosaurs in the Tree of Life?

The premise of the four-shot scene was to depict the birth of consciousness (what some have called the "birth of compassion") -- the first moment in which a living creature made a conscious decision to choose what Michael described as "right from wrong, good from evil." Or, perhaps, a form of altruism over predatory instinct.

Here's the relevant passage from a 2007 draft of Malick's screenplay.

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Tree of Life: The missing link discovered! - scanners: