Page 123 - Science Course 3 (Book 1)
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Mo3-L3a: What is the Evidence for Evolution?
Body parts that perform a similar function but differ Key Concept
in structure are analogous structures.
What is the Evidence for Evolution?
How are vestigial structures evidence of descent
from ancestral species?
Vestigial structures are body parts that have lost
their original function through evolution.
Ambulocelus natans
Between 50-10 million years ago, this mammal
breathed air and walked clumsily on land. It spent a
lot time in water, but swimming was difficult because
of its rear legs, individuals born with variations that
made their rear legs smaller lived longer and
reproduced more. This mammal is an ancestor of SUMMARY
modern whales
What is the Evidence for Evolution?
By comparing the anatomy of organisms and
looking for homologous or analogous
structures, scientists can determine if
organisms had a common ancestor.
Modern Toothed Whale
After 10-15 millions more years of evolution, the
ancestors of modern whales could not walk on land.
They were adapted to an aquatic environment.
Modern whales have two small vestigial pelvic bones Some organisms have vestigial structures,
that no longer support legs. suggesting that they descended from a species
that used the structure for a purpose.
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