Chapter 4: Speciation and Phylogeny

Macroevolution•Species and Speciation

•Phylogenies: Evolutionary Trees

Biological Species

• Reproductive isolation– Gene flow within species– No gene flow between species

• Allopatric speciation: results from geographic/environmental isolation– Selection or gene drift will eventually change

each population in different directions and eventually they will be incapable of interbreeding

• Sympatric Speciation: Niche diversification– Different ways of making a living in the same

place. – Specialization toward different resource

gathering strategies leads to different selective forces

Time

• Sympatric Speciation: Niche diversification– Different ways of making a living in the same

place. – Specialization toward different resource

gathering strategies leads to different selective forces

– Darwin’s finches– Adaptive radiation

Other isolation mechanisms– Mechanical isolation– Temporal isolation– Behavioral isolation

Seagulls around the World

Phylogenies: Trees of Life

• Linnaeus: Linnaean System of Classification• Based on similarity of traits• Hierarchical:

– Kingdom– Phylum– Class– Order– Family– Genius– Species

Kings Play Chess On Fine Grained Sand

Keep Pots Clean Or Family Get Sick

Kingdom: AnimalPhylum: Cordates (Sub phylum Vertebrata)Class: MammalOrder: PrimateFamily: Hominid (Super Family Hominoid)Genius HomoSpecies Sapiens

Humans are:

Phylogeny for the Hominoids

Inheritance or Convergence?

• Homologous = Similar because of common decent (share a recent common ancestor) – Inheritance.

• Analogous = Similar because of adaptation to the same or similar environmentally stable problem (Bird and Bat wings) - Convergence.

Phylogenies use homologous structures (traits) and must avoid

analogous structures

Present

Past

Yes No No

Derived Trait Analogous Trait Ancestral Trait (last common ancestor) (convergence) (common ancestor of all 3)

Using Overall Similarity of Traits Leads to the Wrong Family Tree

Using Similarity of Derived Traits Leads to the Correct Family Tree

Using Similarity of Derived Traits Leads to the Correct Family Tree

Systematics: the study that distinguishes ancestral from derived traits

Ancestral Traits

• Appear earlier in embryonic development– Ontology recapitulates phylogeny

• Appear earlier in the fossil record– Older traits

• Seen in out-groups– If a trait is absence in one species but seen in

other more distant lineages (tails)

Genetic Distance

• DNA Hybridization

Fewer bonds More bonds

Less Related More Related

Lower Temp to break Higher Temp to break

Molecular Clock

Neutral theory or Natural selection?

How Good are Human Phylogenies

•Cladistic modeling of skeletal traits do not match the cladistic modeling of DNA distance

•Human phylogenies are based on skeletal data and are likely to have errors. Some argue for Bastian statistics approach.