Patterns of evolution

#1. TimingGradualism Punctuated Equilibrium

• Rate of evolution is very slow and constant

• (millions of years)

• Evolution occurs in bursts (thousands of years) followed by millions of years of stasis

**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

Fig. 16-11

past

(a) Evolutionary tree (b) Evolutionary tree representingadaptive radiation

In an adaptiveradiation, multiplespeciation eventsmay occur rapidlyenough thatbiologists cannotbe certain of theirorder

present

Forksrepresentspeciationevents

Each linerepresentsa species

time

#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

III. Coevolution: Process in which two species evolve together in response to change in each other

a. 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

#6 Developmental Genescalled hox genes:

Developmental genesChanges 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.