Chapter 15 – Theory of Evolution

15-2: Evidence of Evolution

The Fossil Record Fossil evidence shows a long history of

Earth – constant change + diversityShows 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 FossilFossil

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 In, 1669, Steno proposed the

PRINCIPLE OF PRINCIPLE OF SUPERPOSITIONSUPERPOSITION 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 ageRelative age

States that a fossil is younger or older than another fossil

Absolute ageAbsolute 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.)

BiogeographyBiogeography 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