Chapter 15 – Theory of Evolution 15-2: Evidence of Evolution

The Fossil Record  Fossil evidence shows a long history of Earth – constant change + diversity Shows forms of organisms appeared, lasted for long periods of time, and then disappeared, only to be followed by newer forms of life that also eventually disappeared

Nature of Fossils  Fossil Trace of a long, dead organism Found in sedimentary rock layers Examples:  Shells  Bones  Teeth  Woody stems (plants)  Whole organisms  Molds  Casts

The Age of Fossils PRINCIPLE OF SUPERPOSITION  In, 1669, Steno proposed the PRINCIPLE OF SUPERPOSITION Stated that successive layers of rock or soil deposited on top of one another by wind and water  Layers known as strata  The lowest layer was the oldest; the top layer was the youngest  Fossils found in same layer, are the same age

Geologic Time Scale  Timeline of when organisms existed Based on fossil evidence

The Age of Fossils  Relative age States that a fossil is younger or older than another fossil  Absolute age Its actual age in years Can be determined by radiometric dating

Distribution of Fossils  Fossil Record inferences: Different organisms lived at different times Today’s organisms are different from those in the past Fossils found in adjacent layers are more like each other than fossils found in deeper or higher layers  Lived during same time periods Can compare when and where different organisms existed

Transitional species  The fossil records describes a gradual sequence of forms over time  Transitional species have intermediate features between ancestors + older descendants Example:  Whales

Distribution of Fossils(cont.)  Biogeography Study of the locations of organisms around the world It compares recently formed fossils with types of organisms living in the same geographical area  Shows that new organisms arise in the areas where similar forms already lived  Examples:  Armadillos  Kangaroos

Distribution of Fossils(cont.)  North + South America  Australia

Anatomy & Embryology  Anatomy The study of the body structure of organisms  Homologous Structures  Structures that originated by heredity from a common ancester  Ex. - Forelimbs

Anatomy & Embryology Analogous Structures  Features that have similar functions but do not derive from same ancestral structures  Ex – Wings or Beaks

Anatomy & Embryology Vestigial structures  Structure that seems to serve no function but resembles structures with functional roles in related organisms  Examples:  Tailbone  Pelvic bone in whales/snake  Appendix  Wisdom teeth

Anatomy & Embryology  Embryology Study of how organisms develop  Example:  Vertebrates

Biological Molecules  Organisms that share many traits should have a more recent common ancestor than organisms that share fewer traits  By looking at DNA, RNA, or Amino Acid sequences, scientists can infer common ancestry

Developing Theory  Mid-1900s Integrated theory of natural selection with genetics  Called the Modern Synthesis of Evolutionary Theory  Widely accepted + applied by scientists  Phylogeny  Relationships by ancestry among groups of organisms  Scientists create a phylogenetic “tree” to show relationship/ancestry