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What are homologous structures?
• Structures that are embryologically similar,
but have different functions.
• Suggests inheritance from a common
ancestor
• The forelimbs of the penguin, alligator,
bat, and human all derive from the
same embryological structures.
What are Analogous Structures?
• Have similar functions, but a different
origin
Hummingbird moth
Hummingbird
The wings serve similar functions, but they differ in structure
and derive from different embryological structures.
What are Vestigial Structures?
• Structures that currently have no function,
but were once useful to an ancestor.
Examples
Tailbone in humans
Appendix in humans
More examples of Vestigial Structures
Wings of Ostriches
Eye of a Blind Cave Salamander
Similarities in Embryology
• Similar embryological development among
species indicates a common evolutionary
history.
EXAMPLE
Chicken
Turtle
Rat
Evidence from Molecular Biology
• Similarity in biomolecules such as RNA,
DNA, and proteins indicates a common
evolutionary history.
The amino acid sequences in human hemoglobin
(red blood cell protein) and gorilla hemoglobin differ
by one amino acid, while the hemoglobin molecules
of humans and frogs differ by 67 amino acids.
The more similar the proteins are in different
species, the more closely related the species is
thought to be.