Key Idea.
Section 1
Diagnostic Structures (The "Smoking Gun")
How do we prove relatedness without DNA? We look for diagnostic structures.
These are unique "new" traits that appeared in an ancestor and were passed to all descendants. For example, a specific shape of the ankle bone (Double-Pulley Astragalus) is found only in whales, hippos, camels, and cows.
Section 2
Separating Homology from Analogy
We must be careful not to be fooled by analogous structures (traits that look similar but evolved separately, like wings in birds and bugs).
Diagnostic skeletal structures (like the ear bone shape) are safer evidence because they are complex and internal. It is highly unlikely that two unrelated species would randomly grow the exact same weirdly-shaped ear bone.
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Section 1
Diagnostic Structures (The "Smoking Gun")
How do we prove relatedness without DNA? We look for diagnostic structures.
These are unique "new" traits that appeared in an ancestor and were passed to all descendants. For example, a specific shape of the ankle bone (Double-Pulley Astragalus) is found only in whales, hippos, camels, and cows.
Section 2
Separating Homology from Analogy
We must be careful not to be fooled by analogous structures (traits that look similar but evolved separately, like wings in birds and bugs).
Diagnostic skeletal structures (like the ear bone shape) are safer evidence because they are complex and internal. It is highly unlikely that two unrelated species would randomly grow the exact same weirdly-shaped ear bone.
Book overview
Jump across lessons in the current chapter without opening the full course modal.
Continue this chapter