Fundamental aspects of evolution:
Phylogeny: Scienti c study of evolutionary relationships among species (represented in phylogenic
tree)
Patterns represented in tree of life:
• Stasis/Equilibrium: lineages don't change for a long time
• Lineage-splitting (speciation):
- Cladogenesis: Evolutionary splitting event where parent species splits into 2 distinct species
(forms a clad): single branch on phylogenic tree
- Anagenesis: Ancestral species gradually changes and can eventually be labelled as new species
- Cladogenesis: Is more important in evolution than anagenesis. Cladogenesis associated with
macro-evolution. Anagenesis associated with micro-evolution
• Adaptive radiation: Burst of divergence from single lineage to give rise to many new species
- eg. 315 m.y.a, reptiles became terrestrial
- Similar rapid burst of diversi cation gave rise to birds
- After dinosaur extinction, mammalian explosion occurred
, • Extinction:
- Regular background extinctions (natural)
- Mass extinctions (catastrophic events)
Trends in macro-evolution:
• Increased complexity eg. prokaryotes to eukaryotes
• Increased body size eg. Horses & cranial capacity
• Evolving from marine habitats to terrestrial habitats
Rate of change in evolution:
• Gradualism: Species evolve by small changes over long time eg. evolution of humans
• Punctuated equilibrium: Speed at which evolution takes place
- Equilibrium alternated with short periods of time where rapid changes occurred through natural
selection
- As a result, new species formed in short periods of time
Phylogeny: Scienti c study of evolutionary relationships among species (represented in phylogenic
tree)
Patterns represented in tree of life:
• Stasis/Equilibrium: lineages don't change for a long time
• Lineage-splitting (speciation):
- Cladogenesis: Evolutionary splitting event where parent species splits into 2 distinct species
(forms a clad): single branch on phylogenic tree
- Anagenesis: Ancestral species gradually changes and can eventually be labelled as new species
- Cladogenesis: Is more important in evolution than anagenesis. Cladogenesis associated with
macro-evolution. Anagenesis associated with micro-evolution
• Adaptive radiation: Burst of divergence from single lineage to give rise to many new species
- eg. 315 m.y.a, reptiles became terrestrial
- Similar rapid burst of diversi cation gave rise to birds
- After dinosaur extinction, mammalian explosion occurred
, • Extinction:
- Regular background extinctions (natural)
- Mass extinctions (catastrophic events)
Trends in macro-evolution:
• Increased complexity eg. prokaryotes to eukaryotes
• Increased body size eg. Horses & cranial capacity
• Evolving from marine habitats to terrestrial habitats
Rate of change in evolution:
• Gradualism: Species evolve by small changes over long time eg. evolution of humans
• Punctuated equilibrium: Speed at which evolution takes place
- Equilibrium alternated with short periods of time where rapid changes occurred through natural
selection
- As a result, new species formed in short periods of time
