Key Idea.
Section 1
The "1-2-Many" Pattern
When we look inside the limbs of mammals (human, cat, whale, bat), we find the exact same bone arrangement: One bone (humerus) Two bones (radius/ulna) Many small bones (wrist) Digits.
This specific pattern is a Homologous Structure. It is mathematically improbable that all these distinct species developed the exact same complex bone layout by accident.
Section 2
Modification of the Blueprint
Evolution rarely invents new parts from scratch; it modifies existing ones. Think of it like remodeling a house rather than building a new one.
The "blueprint" (the 1-2-Many bone pattern) comes from the ancestor. A whale's flipper is just a "remodeling" of that ancestor's arm—the bones are shortened and flattened to push water, but they are still the same bones.
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Section 1
The "1-2-Many" Pattern
When we look inside the limbs of mammals (human, cat, whale, bat), we find the exact same bone arrangement: One bone (humerus) Two bones (radius/ulna) Many small bones (wrist) Digits.
This specific pattern is a Homologous Structure. It is mathematically improbable that all these distinct species developed the exact same complex bone layout by accident.
Section 2
Modification of the Blueprint
Evolution rarely invents new parts from scratch; it modifies existing ones. Think of it like remodeling a house rather than building a new one.
The "blueprint" (the 1-2-Many bone pattern) comes from the ancestor. A whale's flipper is just a "remodeling" of that ancestor's arm—the bones are shortened and flattened to push water, but they are still the same bones.
Book overview
Jump across lessons in the current chapter without opening the full course modal.
Continue this chapter