Unit 7 (Evidence of Evolution)

Primary sources of evidence for evolution

• The fossil record

• Comparative morphology

• Biogeography

Fossil Record

• Fossil: remains or traces of past organisms

• Fossil record: gives a visual of evolutionary change over time

• Fossils can be dated by examining rate of Carbon 14 decay and the age of rocks where the fossils are found

  • Gives geographical data for the organisms found

Comparative Morphology

Analysis of the structure of living and extinct organisms

• Homology: Characteristics in related species that have similarities, even if the functions differ

  • Similar structure, different function

• Embryonic homology: many species have similar embryonic development

• Molecular homology: many species share similar DNA and amino acid sequences

Vestigal structures

Structures that are conserved even though they no longer have a use (ex. tailbones and appendix)

Homologous structures

Characteristics that are similar in two species because they share a common ancestor (ex. arm bones)

Convergent evolution

Similar adaptations that have evolved in distantly related organisms due to similar environments

• Analogous structures: structures that are similar but have separate evolutionary origins (ex. wings in birds vs bats vs bees)

  • Each species has wings, but the wings did not originate from a common ancestor

Common ancestry of all eukaryotes

• Indicated by structural evidence

• Many fundamental and cellular features and processes are conserved across organisms

• Cellular examples:

  • Membrane-bound organisms

  • Linear chromosomes

  • Introns in genes

Biogeography

The distribution of animals and plants geographically

• Species on oceanic islands resemble mainland species

• Species on the same continent are similar and distinct from species on other continents

Phylogeny

• Systematics: classification of organisms and determining their evolutionary relationships

• Taxonomy: naming and classifying species

• Phylogenetics: hypothesis of evolutionary history

  • Use phylogenetic trees to show evolution

How to determine evolutionary relationships

• Fossil records

• DNA

• Proteins

• Homologous structures

Phylogenetic Trees

Diagram that represent the evolutionary history of a group of organisms

• Similar to cladograms, except trees show the amount of change overtime measured by fossils

Cladograms

• Each line represents a lineage

• Each branching point is a node

• Nodes represent common ancestors

  • Nodes and all branches from it are called clades

  • Species in a clade have shared derived features

• The root is the common ancestor of all the species

• Two clades that emerge from the same node are sister taxa

• A lineage that evolved from the root and remains unbranched is the basal taxon

Synapomorphy

A derived character shared by clade members

• Derived characteristics: similarity inherited from the most recent common ancestor of an entire group

• Ancestral characteristic: similarity that arose prior to the common ancestor

• Many cladograms and trees include an out group

  • A lineage that is the least closely related to the rest of the organisms

Monophyletic group

Includes the most recent common ancestor of the group and all of the descendants (clade)

Paraphyletic group

Includes the most recent common ancestor of the group, but not all its descendents

Polyphyletic group

Does not include the most recent common ancestor of all members of the group

Parsimony

If there are conflicts among characters, use the principle of parsimony

• Use the hypothesis that requires the fewest assumptions (DNA changes)