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The following items demonstrate descent with modification, as well as common ancestry. (Darwin’s principle of common descent)
I -Fossil EvidenceI -Fossil Evidence (descent with modifications) (descent with modifications)
Horse fossils indicate changes in size,
as well as the transition from toes to hooves.
I - Fossil Evidence:I - Fossil Evidence: ContinuedContinued
These mollusk
fossils show
the development
of torsion, the
twisting of
their shells.
II -Homologous StructuresII -Homologous Structuresare fundamentally similar in their makeup, position and are fundamentally similar in their makeup, position and development, but are adapted to different functions. development, but are adapted to different functions.
Animal Forelimbs:
The Galapagos finch beaks are said to
be homologous. They originated in a
common ancestor and have adapted to
various environments.
Homologous v. Analogous What’s the Difference?
Homologous structures are features that originated in a shared ancestor. They have different mature forms, but develop from the same embryonic tissue.
They are inherited from a common ancestor.
Analogous Structures have features that have identical functions, and look somewhat alike, but they may be different in internal anatomy.
The evolved independently after their point of common ancestry, so they were not inherited from a common ancestor.
A bird’s wing and a moth’s wing are analogous. They allow the animals to fly, butThey have greatly different development and internal
structure.
III -Vestigial StructuresIII -Vestigial Structureswhich may have been functional in an ancestor, are which may have been functional in an ancestor, are
functionless and underdeveloped in later generationsfunctionless and underdeveloped in later generations Human tailbone (coccyx)
Human Appendix
III - Vestigial Structures: III - Vestigial Structures: Structures that are vestigial in one organism, may be Structures that are vestigial in one organism, may be
functional in others.functional in others.
Nictitating membrane
Ear muscles
III - Vestigial Structures III - Vestigial Structures (continued):(continued):
Limb bones in snakes
Pelvic bones in whales
III – Vestigial Structures:III – Vestigial Structures:ContinuedContinued
• Erector pili muscleswhich cause “goose bumps”in humans
• Human baby born with fleshy tail
IV -Embryological Similarities
Various embryos in early stages showevidence of gills slits and tails.
V - Biochemical EvidenceV - Biochemical EvidenceAll organisms have DNA (& RNA)
All organisms have ATP
Similarities in cell respiration enzymes
V- Biochemical EvidenceV- Biochemical Evidence(Continued)(Continued)
All organisms have cytochrome c
in the electron transport chain
(The difference in A.A.s is proportional to the length of time that has passed since the two shared a common ancestor.)
VI – Homeotic GenesHomeotic genes (Hox genes): regulatory genes that
determine where certain anatomical structures, such as appendages will develop in an embryo. “They seem to be master genes of development that determine the overall body organization.”
Common ancestry is demonstrated because animals share many of these Hox genes, which may control the development of similar regions.
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