Summary:
- Invertebrates evolved several important traits before vertebrates even appeared.
- These traits are now found in just about all animals.
- The first animal trait to evolve was multicellularity.
- Multiple cells could do different jobs and evolve special adaptations.
- Evolution of tissues was the first step in the evolution of organs and organ systems.
- Cephalization is the concentration of nerve tissue at one end of the body, forming a head region.
- This is highly adaptive and allows central control of the entire organism.