Chapter 5 The Forces of Evolution And The Formation of Species

How Evolution Works Where Does Variation Come From? Mutations Point mutation Chromosomal mutation

How Evolution Works (cont’d) How Natural Selection Works Phenotypes in environments Changes in gene frequencies Directional Selection/ Stabilizing Selection

How Evolution Works (cont’d) Other Ways By Which Evolution Happens Gene Flow: movement of genes between populations Genetic Drift: random changes in gene frequency in a population Founder Effect: genetic bottleneck Sexual Selection: Differential reproductive success within one sex of any species

Classification and Evolution Taxonomy and Speciation Systematics: branch of biology that describes organismal variation (what used to be called taxonomy) Homology: the notion that similar features in two related organisms look alike because of a shared evolutionary history Analogy: the notion that similar features in two unrelated organisms look alike because of adaptations to similar functions. (Convergent (parallel) evolution)

Classification and Evolution (cont’d) Cladistics Cladograms Phenetics: numerical taxonomy What is a Species? An interbreeding group of animals or plants that are reproductively isolated through anatomy, ecology, behavior, or geographic distribution from all other such groups (Mayr, 1942)

Classification and Evolution (cont’d) Species Concepts Biological species concept Evolutionary species concept Ecological species concept Recognition species concept

Classification and Evolution (cont’d) Reproductive Isolating Mechanisms (RIMs) Any factor that prevents a male and female of two different species from hybridizing Premating RIMs Postmating RIMs

Classification and Evolution (cont’d) Premating RIMs Habitat isolation Temporal isolation Behavioral isolation Mechanical incompatibility Postmating RIMs Sperm-egg incompatibility Zygote inviability Embryonic or fetal inviability Offspring inviability Offspring sterility

Classification and Evolution (cont’d) The Origin of Species: how species are formed Anagenesis (whole group, no branching) Cladogenesis (splitting events; branching) Allopatric speciation (geographic isolation) Parapatric speciation (separate habitats) Sympatric speciation (form of anagenesis)

Classification and Evolution (cont’d) The Tempo of Speciation Gradualism Darwinian Gaps? Macroevolution Punctuated equilibrium

Classification and Evolution (cont’d) Adaptation (Is everything adaptive?) Adaptations are evolved phenotypic traits that increase an organism’s reproductive success

Classification and Evolution (cont’d) Hardy-Weinberg Equilibrium (p + q)2 = p2 + 2pq + q2 = 1

Levels of Selection Group selection Inclusive Fitness Behavioral ecology Kin selection Coefficient of relatedness rb > c Hamilton’s Rule