Benchmark 5F
The Living Environment: Evolution of Life
Grades 6-8, page 124

Small differences between parents and offspring can accumulate (through selective breeding) in successive generations so that descendants are very different from their ancestors.

NSES Content Standard C 
Life Science: Regulation and behavior
Grades 5-8, page 157
An organism's behavior evolves through adaptation to its environment. How a species moves, obtains food, reproduces, and responds to danger are based in the species' evolutionary history.

NSES Content Standard C
Life Science: Diversity and adaptations of organisms
Grades 5-8, page 158
Biological evolution accounts for the diversity of species developed through gradual processes over many generations. Species acquire many of their unique characteristics through biological adaptation, which involves the selection of naturally occurring variations in populations. Biological adaptations include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment.