GEOL 104 Dinosaurs: A Natural History
Fall Semester 2005
Evolution I: Descent with Modification
Cuvier, Owen, and other early anatomists observed same underlying anatomical structures
in closely related forms:
Homologous structures: the same anatomical structure, regardless of function.
For example, humans and dinosaurs and other vertebrates have the same
bones in the skeleton, even though those bones are shaped differently.
Comparative anatomy seeks to describe the structure of the bodies of organisms in terms
of their homologous structures.
Also noticed a different type of anatomical similarity:
Analogous structures: represent different units of anatomy serving the same function.
Why does comparative anatomy work (i.e., where are their homologies)?
Why are there adaptations (specialized structures or behaviors that allow
organisms to interact with their environment in certain specific ways)?
Why is Life so effectively organized under a nested hierarchy of groups?
Why should the Principle of Fossil Succession work?
Where should vestigial organs exist?
Why should groups closely related to each other have embryos similar throughout most of their development, while those of more distantly related forms have fewer shared stages?
Why does the fossil record hold evidence of creatures intermediate in form between distinct modern groups?
Why is there a biogeography (non-random distribution of living things)?
FROM WHERE DO NEW SPECIES COME?
Evolution: descent with modification
New species are the modified descendants of previously existing species.
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Last modified: 14 July 2006