1. Macroevolution
Major innovations  separation at higher taxonomic levels
Exaptation
Existing feature modified to perform novel function
Ex: Development of bird wings from reptiles forelimbs not designed for flight
Some plasticity in biological structures
Ex: Bird feathers evolved from reptile scales
May have provided insulation for primitive birds
Preadaptation for flight
Ex: Middle ear bones in mammals evolved from jaw bones in reptiles
Does not imply that structures developed in anticipation of future use

2. Macroevolution Developmental Rate and Timing
Some evolutionary modifications result from minor genetic changes
Heterochrony
May affect regulatory genes
Ex: Allometric growth – Changes in relative growth rates of body parts during development

3. Prolonged
juvenile
period
Fig

4. Macroevolution Developmental Rate and Timing
Paedomorphosis – Retention of juvenile characteristics in adults
Fig

5. Macroevolution Changes in Spatial Pattern
Some genes control spatial organization of body parts
Ex: Homeotic genes regulate organism’s bauplan
Hox genes provide positional information in animal embryos
Purple:
HoxC6 expression
(limbless regions)
Fig

6. Macroevolution Changes in Spatial Pattern
Regulatory changes may affect gene expression without changes in gene sequence
Fig

7. Macroevolution
Directionality
Macroevolution not goal-oriented

8. Fig.
25.27

9. Phylogeny and Systematics
Evolutionary processes reflected in organismal phylogeny
Genealogies often represented as phylogenetic trees that reflect relationships among species
Systematics deals with classification of taxa according to evolutionary history

10. Fig. 26.4