NSES Content Standard C 
Life Science: Diversity and adaptations of organisms
Grades 5-8, page 158

Millions of species of animals, plants, and micro-organisms are alive today. Although different species might look dissimilar, the unity among organisms becomes apparent from an analysis of internal structures, the similarity of their chemical processes, and the evidence of common ancestry.

Benchmark 5A The Living Environment: Diversity of Life
Grades 6-8, page 104
Similarities among organisms are found in internal anatomical features, which can be used to infer the degree of relatedness among organisms. In classifying organisms, biologists consider details of internal and external structures to be more important than behavior or general appearance.

Benchmark 5A The Living Environment: Diversity of Life
Grades 9-12, page 105
The degree of kinship between organisms or species can be estimated from the similarity of their DNA sequences, which often closely matches their classification based on anatomical similarities.

Benchmark 5F The Living Environment: Evolution of Life
Grades 9-12, page 125
Molecular evidence substantiates the anatomical evidence for evolution and provides additional detail about the sequence in which various lines of descent branched off from one another.