Ecosystem isn't just a video game version of the laws of ecology with pre-made fish models. The simulation actually determines the creatures in the game: their bodies, how they swim, and how they think and behave. All the creatures in the trailer evolved on their own in the game; none were hand-edited!
Virtual creatures
At Ecosystem's heart are evolving virtual lifeforms, who grow from synthetic DNA and live in a physically-simulated ocean. This synthetic DNA encodes everything about a creature, from skeletal structure to skin, from joint-types to mental processes. The genetic code of a creature can mutate, combine, be spliced with other species, and be directly modified by the player. Creature brains are also encoded in DNA and subject to evolution. The neurology of a virtual lifeform is a pipeline computer where, every moment, data from sense organs is passed through a network of neurons and finally contracts a muscle in a specific body part.
Movement is bound by the laws of fishics
To swim, creatures don't just play an animation. They move like real sea-life, applying torque at their joints to push against the water in a way coordinated to propel themselves forward. Working within this physical simulation, evolution can produce an enormous variety of body shapes and swimming styles. A wide variety of different creature populations share a single environment, where they swim, graze, prey on each other, and have children. The fittest creatures pass their genes along to their children, and over time a world of strange and unique creatures is born...
