Chapter 26Phylogeny and the

Tree of Life

Phylogeny

Phylon = tribe, geny = genesis or origin

The evolutionary history of a species or a group of related species.

Phylogeny

Found in the fossil record, molecules and genomes.

Systematics

The study of biological diversity and classification.

Uses evidence from the fossil record and other sources to reconstruct phylogeny.

Systematics fuses:

1. Phylogeny- tracing of evolutionary relationships.

2. Taxonomy- the identification and classification of species.

Taxonomy

Natural to humans. Modern system developed by

Linnaeus in the 18th century.

Linnaeus Taxonomy

1. Binomial Nomenclature – two names for each organism.

Ex - Homo sapiens

2. Hierarchical System – arranges life into groups. Ex - Kingdom Species: List

Scientific names

Composed of Genus and species.

Written in Latin and shown in italics or underlined.

Governed by a set of rules and procedures.

Goal of Systematics

To have Taxonomy reflect the evolutionary affinities or phylogeny of the organisms.

Phylogenetic Tree

Branching diagram showing evolutionary relationships between organisms.

Phylogenetic tree - Example

Trees show:

Ancestral lineage Branch points or nodes Length of branch point

suggests “time” and degree of closeness.

Phylogenetic tree - Example

Branch pointAncestral Lineage

Ideal Situation

Monophyletic Grouping - a single ancestor gave rise to all species in the taxon.

Other Possibilities

Polyphyletic - grouping where members are derived from two or more ancestral forms.

Paraphyletic - grouping that does not include all members from an ancestral form.

Problem

Not all “likeness” is inherited from a common ancestor.

Problem is of homology vs analogy.

Homology and Analogy Homology – likeness attributed

to shared ancestry. Ex: forelimbs of vertebrates

Analogy – likeness due to evolution solution for the same problem. Ex: wings of insects and birds

Convergent Evolution

When unrelated species have similar adaptations to a common environment. A specific example of Analogy.

Ex: Sharks and dolphins

Only one is a cactus

Need

Methods to group organisms by similarities and phylogenies.

One possible method is Molecular Systematics.

DNA patterns

If similar DNA – more closely related, more recent common ancestor.

If different DNA – less closely related, less recent common ancestor.

Making a Phylogenetic Tree

May use morphology, genetic and other data.

Uses statistical analysis looking for “best fit”.

Best Fit

Maximum parsimony – requires fewest DNA base changes.

Branch lengths – suggest the closeness of the relationships and the time of branch points.

Result

Taxonomy will become Genealogies, reflecting the organism’s "Descent with Modification“.

5 Kingdom System

R.H. Whittaker - 1969 System most widely used,

but is changing.

Main Characteristics

Cell Type Structure Nutrition Mode Problems in Kingdom Monera

and Protista

Current Views

Multiple Kingdoms – split life into as many as 8 kingdoms.

Domains – a system of classification that is higher than kingdom.

3 Domain System

Based on molecular structure for evolutionary relationships.

Prokaryotes are not all alike and should be recognized as two groups.

3 Domains

1. Bacteria – prokaryotic.

2. Archaea – prokaryotic, but biochemically similar to eukaryotic cells.

3. Eukarya – the traditional eukaryotic cells.