Paraphyletic Group
A common ancestor and some, but not all, of the ancestor’s descendants
Polyphyletic Group
Group of branches that doesn’t include common ancestor of group
Monophyletic Group
Common ancestor and all of its descendants
Synapomorphy
Shared derived trait present in 2 or more related organisms, indicating a common ancestor
Homoplasy
Trait shared by different species that lack a common ancestor, arose through convergent or parallel evolution
Convergent Evolution
Adapting to similar environmental pressures -> 2 or more unrelated species independently evolve similar traits or features -> structures with similar functions despite no common ancestor (analogous)
Molecular Clock
Rate of molecular evoltion at same gene relatively constant across lineages -> estimate when species diverged from common ancestor
Pros of Fossils
-Show extinct and transitional organisms
-Environmental changes
-Calibrate time
Adaptive Radiation
-Common ancestor
-Rapid diversification within a lineage
-Trait-environment adaptation in context of ecological opportunity
Sister Taxa
Monophyletic groups that are more closely related to each other than they are to any other group in the tree
Parsimony
The assumption with the fewest evolutionary steps (simplest) is the most likely
Vicariance Hypothesis
Island originally part of mainland but rise in sea level caused it to become isolated -> island mammals diverged from mainland ancestors
(physical barrier -> speciation)
Dispersal Hypothesis
Ancestors of current island species dispersed independently at different times from the mainland to island -> divergence from mainland species
Cladogram
Branch lengths arbitrary, emphasis on branching pattern which estimates evolutionary relationships among populations through traits, looks like half the veins of a leaf
Phylogram
Horizontal branch lengths show extent of genetic difference among population, includes scale bar
Chronogram
Horizontal branch lengths show evolutionary time between nodes, includes scale bar
Mechanisms of Evolution
(Violations of Hardy-Weinberg Equilibrium)
1.) Natural selection
2.) Mutations
3.) Genetic Drift
4.) Gene flow (migration)
5.) Assortative mating
Characteristics of Evolution by Natural Selection
-Heritability
-Variation in population
-Differences in fitness
-Limited population growth (selective pressure needed)
Indirect Fitness
Helping a family member produce offspring which helps pass on some of your own genes (kin selection)
Directional Selection
Favors 1 extreme, increases or decreases mean trait value
Stabilizing Selection
Favors mean, variability decreases -> makes graph more narrow
Disruptive Selection
Favors both extremes, if both selected for equally -> mean wouldn’t change
Hamilton’s Rule
rB>rC
Where:
r=relatedness
B=net benefit
C=cost to person helping
Biological Species Concept
Species can produce fertile offspring (reproductive isolation)
