Patterns of evolution

#1. Timing Punctuated Equilibrium Gradualism Evolution occurs in bursts (thousands of years) followed by millions of years of stasis Rate of evolution is very slow and constant (millions of years) **Note in geologic time “short” and “rapid” can mean hundreds of thousands to millions of years! The fossil record shows both of these theories as possibilities.

More on punctuated Equilibrium Evidence that evolution occurs more rapidly following environmental change

#2 Divergent/Adaptive Radiation Species evolve to look different Often times many groups evolve from one common ancestor

Example Darwin’s Finches on the Galapagos Islands: one species from the mainland evolved into many species

Fall of dinosaurs gave rise to adaptive radiation of mammals

Interpreting Evolutionary Trees present Each line represents a species In an adaptive radiation, multiple speciation events may occur rapidly enough that biologists cannot be certain of their order time Forks represent speciation events past (a) Evolutionary tree (b) Evolutionary tree representing adaptive radiation Fig. 16-11

#3 Convergent Different species evolve to appear similar despite different ancestry = NO RECENT COMMON ANCESTOR Leads to formation of analogous structures

Example – Placental vs. marsupial mammals

Example of analogous structures - wings

Coevolution: Process in which two species evolve together in response to change in each other Examples: Orchid and moth, insects and plant poison, hummingbird & flower structure.

Example – milkweed and Monarch Butterflies Milkweed is toxic Monarch butterflies feed on milkweed and have evolved to withstand the toxin They become toxic to predators

#4 Aposematic coloration Prey evolve very bright coloration Predators have evolved to avoid butterflies with bright coloration

#5 mimicry Harmless species evolve to appear similar to toxic/dangerous species

Changes during the embryonic stage can have a huge effect. #6 Developmental Genes called hox genes: Developmental genes Changes during the embryonic stage can have a huge effect. This lends itself to patterns in morphology: heads, trunk, legs being an example. http://www.pbs.org/wgbh/evolution/library/03/4/l_034_04.html Hox gene video (~5 min)

MACROEVOLUTION practice quiz HW Quiz next class-allele frequency (not the math just the concept behind why they shift), causes of microevolution, phylogenic trees, species, patterns of evolution.