1. Chapter 18: Evolution and Origin of Species

2. What is Evolution? Species is a group of interbreeding organisms.
Populations are well adapted to their environments meaning certain traits allow them to survive and reproduce
Genetic variation which is maintained through mutations and sexual recombination.
Changes in the environment may allow rare variations to be more adapted and increase in frequency.
Adaptive radiation one species spread to different environments adapting to each one

3. Observational evidence of evolution
Comparative morphology: Study of anatomical patterns of different species
19th century naturalists had difficulty explaining vestigial structures
Fossils: physical evidence of an organism that lived in ancient past
Fossils are found in stacked layers of sedimentary rock (Geologic column)
Modern observations of comparative biochemistry ( DNA and proteins)

4. Homology
Homologous structures – shared structures present as explained by common ancestry
Become modified to a different size, shape, or function in different lineages
Morphological divergence - change away from the ancestral form
Explains the presence of vestigial structures

6. Darwin explains the diversity of species
Based on observations during a trans-global trip.
Populations produces more offspring than can survive
Populations have variation
Certain variations increase chance of survive and reproduction
Favored traits are passed on to offspring
Darwin published “On the Origin of Species by Means of Natural Selection”
Promoted the idea that species are related by a common ancestor.

8. Speciation
Groups within a populations become reproductively isolated and can no longer interbreed
These subgroups accumulate more genetic variation and are no longer able to reconnect.
Allopatric speciation – populations separated by geographic barrier
Sympatric speciation – populations not separated but no longer interbreed due to other factors
Due to definition of species it is difficult to determine if speciation has occurred.

11. Chapter 19 Evolution of Populations

12. Populations Evolve Populations are the only units of evolution.
Higher levels of classification evolve independent of each other.
Because each populations shares alleles that occur in frequencies that may change over time.
Hardy-Weinberg developed a formula showing how frequencies of alleles will remain the same (do not evolve).
Population genetics is the study of how populations “gene pool” changes

14. Mechanisms of evolution
In order for p and q to change populations are subjected to “forces”
Genetic Drift – random variations in the offspring.
Bottleneck – small sample of larger will have different allele frequency.
Migration – individuals from different populations mix frequently; can maintain genetic variation of a populations
Mutations – necessary for creating new alleles usually cannot affect populations by themselves

15. Natural Selection
Certain traits have higher “adaptive value” meaning they make up a larger proportion of the next generation.
Directional – the extreme of on trait is selected
Stabilizing – selects against both extremes of a trait
Diversifying – selects both extremes of a trait
Sexual selection – traits that only increases reproduction success are selected

16. Chapter 20:Phylogenies and History of Life

18. Classification Linneaus develops earlier hierarchal system.
Organisms are groups by shared characteristics
Modern classification systematics
The goal of systematics is to reflect evolutionary relationships.
Biologists use phylogenetic trees to:
Depict hypotheses about the evolutionary history of species
Reflect the hierarchical classification of groups within more inclusive groups

19. Taxonomy Rankings Domain Kingdom Phylum Class Order Family Genus
Species

21. Using Homology Homologous structures the best source of information
Molecular Systematics compares DNA and sequences between organisms (even some fossils)
Excludes convergent traits – similar in function but not same origin

24. Clades Cladistics - Method of determining evolutionary relationships
Groups species into clades which includes ancestor and all descendants
Each clade is represented by a branch or groups of branches
Results in a cladogram