Bilateral symmetry allowed animals to evolve heads and directed movement
The evolution of bilateral symmetry 610 million years ago allowed animals to develop heads, concentrated sensory organs, and the ability to move purposefully through their environments.
Approximately 99% of all animal species belong to the Bilateria, a group defined by a symmetrical body plan with distinct left and right sides. This evolutionary leap, occurring around 610 million years ago, facilitated cephalization—the concentration of nerve tissues and sensory organs into a head. Unlike radial animals like jellyfish, which drift or react to stimuli from all directions, bilateral animals can move with intent, leading to more efficient hunting and navigation.
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