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Evolutionary Trends in Animals

Cell Specialization

Over time, animals evolve and their cells begin to specialize and carry out certain tasks such as muscle cells for movement and bone cells for structure. As multicellular organisms develop, groups of cells become tissues, and tissues become organs and organ systems. As animals become influenced by their environment, they develop traits to adapt to their surroundings and meet the requirements to survive. Lizards' claws enabled them to fend off predators and kill prey, or to grip on rocks and cliffs. Animals from the same environment develop similar characteristics and as the environment change, new characteristics are found among animals showing a trend throughout evolution.

Trends in Evolution Diagram

As you progress down the chart, organisms become more complex and have higher levels of cell specialization and internal body organization. Further down, you will see animals starting to have bilateral body symmetry, a front or head with sensory organs, and a body cavity (Prentice Hall Biology page 660). In the chart you can see how most organisms share a common ancestor and all originated from ancestor species.