Tracing Evolutionary History: Phylogeny and the Tree of Life

1. The evolutionary history of a species or group of species
2. Fossil record provides information about timing of evolutionary divergences
3.Homologous morphological traits, behaviors and molecular sequences also provide evidence of common ancestry

1. Result from convergent evolution in similar environments
2. These similarities do not provide information about evolutionary relationships

Classifies organisms and determines their evolutionary relationship

1. Assign each species a binomial consisting of a Genus and species name
2. Genera are grouped into progressively larger categories
3. Each taxonomic unit is a taxon

A hypothesis of evolutionary relationships within a group

1. Uses shared derived characters to group organisms into clades including ancestral species and all its descendents
2. An inclusive clade is monophyletic
3. Shared ancestral characters were present in ancestral groups
4. Comparison of the ingroup and the outgroup

The taxa whose phylogeny is being investigated

A taxon that diverged before the lineage leading up to the members of the ingroup

1. Shows that crocodilians are the closest living reptiles of birds
2. They share numerous features including four-chambered hearts, singing to defend territories and parental care of eggs within nests
3. These traits were probably present in the common ancestor of birds and crocodiles

1. Compares nucleic acids or other molecules to infer relatedness of taxa
2. The more recently two species have branched from a common ancestor the more similar their DNA sequences should be
3. The longer two species have been on separate evolutionary paths the more their DNA should diverge
4. Homologous genes have been found in organisms separated by large evolutionary distances

1. Used to estimate sates of divergences without a good fossil record
2. Can be calibrated in real time by graphing the # of nucleotide differences against the dates of evolutionary branch points known from the fossil record
3. Some regions of the genome appear to accumulate changes at constant rates

1. Transfer of genes between genomes by plasmid exchange, viral infection and fusion of organisms
2. Two major episodes:
3. Gene transfer between a mitochondrial ancestor and the ancestor of eukaryotes
4. Gene transfer between a chloroplast ancestor and the ancestor of green plants

1. Ribosomal coding (rRNA) is used to investiagte the relationships between taxa that diverged hundreds of millions of years ago
2. Mitochondrial coding (mtDNA) evolves rapidly and is used to show relationships between taxa that diverged thousands of years ago (ex. divergence of Native American tribes from 13,000 years ago)