Chapter 18: Evolution and Origin of Species

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

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)

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

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.

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.

Chapter 19 Evolution of Populations

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

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

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

Chapter 20:Phylogenies and History of Life

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

Taxonomy Rankings Domain Kingdom Phylum Class Order Family Genus Species

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

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