Macroevolution

Macroevolution is the study of major
biological changes evident in the fossil
record

Includes the following:
1.
Multiplication of species
2.
Origin of structures like feathers and
large brains
3.
Diversification of species – like flowers
4.
Mass extinctions that lead to explosions like the explosion of mammals after the
dinosaurs became extinct
speciation

Speciation is the origin of new species

Branching vs. non-branching

Branching – a lineage is split into two
or more species

Non-branching – initial species
becomes new species
Anagenesis vs.
Cladogenesis
The Origin of Species

Biological species concept – groups of
interbreeding natural populations
whose members ONLY breed with
each other to create fertile offspring.

What keeps members of different
species apart?
Reproductive Barriers

Prezygotic barriers – occur before
conception

Post-zygotic barriers – occurs after
conception
Pre-zygotic Barriers

Temporal Isolation –
mating or flowering
occur at different time
of the year/day
Ex. Western spotted
skunks breed in fall,
while eastern spotted
skunks breed in the
late winter

Habitat Isolation –
species living in the
same region may
occupy different
habitats
Ex. Some Garter snakes
live in water/some on
land

Behavioral
Isolation-courtship
rituals are very
specific
Ex. Birds

Mechanical
isolation-structural
differences in
genitalia or flowers
prevent copulation
or pollen transfer
Ex. Insects and flowers

Gametic isolationmale sperm cannot
fertilize the egg
Post-zygotic Barriers

Hybrid Inviability – hybrid zygotes
fail to develop or reach sexual
maturity

Hybrid Sterility – Hybrid individuals
fail to produce young
Speciation

When a
population is
somehow severed
from the parent
population and
over time its gene
pool is altered.

Allopatric and
sympatric
Allopatric speciation

Isolation is the result of a
geographic barrier

Ex. Galapagos finches

True speciation only occurs if the
remaining populations will NOT
breed
allopatric
Sympatric

When a sub-population arises in the
midst of the parent population

Many plant species have accidental
polyploidy in meiosis. They produce
zygotes with multiple sets of
chromosomes.

They can no longer reproduce with
parental generation.
Evolution of Wheat
What is the tempo of
speciation?

Gradual vs. punctuated

Punctuated equilibrium model –
species most often diverge in spurts of
rapid change instead of slow and
gradually.

Over a few to ten thousand years,
genetic drift and natural selection can
change small, isolated species
Punctuated
Equilibrium
Archaeopteryx
Exaptation

Term used to describe a structure
that evolves in one context, but
becomes adapted for another.
However, natural selection cannot
anticipate future need
Ex. Light bones in reptiles
Evo-Devo

How do evolution and development
interface?

Genes control the development of an
organism from zygote to adult

Turning these genes on and off at
certain times can have a profound
effect on development.

Paedomorphosis – the retention of
juvenile features as an adult

Ex. axototl
Axototl
Chimpanzee vs. human
skulls

We retain a skull
more like that of
our fetal skull
History of biological
diversity

Macroevolution is tied to the history
of the Earth

Fossils are recovered from various
sources
Sedimentary rocks
Skulls
Petrified trees
Tracks
Body parts
Amber
Geological Time Scale

Four eras – Precambrian, Paleozoic,
Mesozoic, Cenozoic

Fossils are dated by carbon dating

Handout

At the end of the paleozoic era (250mya),
Pangaea was formed.

The formation of pangaea reduced
coastline and changed the environment
for many terrestrial species.

Changing ocean currents killed many
marine species
Breaking of Pangaea

180 MYA during the mesozoic

Caused major geographic isolation
Continental drift
Patterns of Evolution



Divergent evolution – when two
isolated population evolve
independently (Ex. Brown and
polar bears)
Adaptive radiation – rapid
evolution of a variety of species
from a single ancestor (ex.
Darwin’s finches)
Convergent Evolution – when two
organisms without a common
ancestor occupy the same niche, so
they have the same characteristics.
(ex. Porpoise and penguin)
Patterns cont.

Parallel Evolution – two related
species who have made similar
evolutionary changes. Ex. Placental
and marsupial wolf

Co-evolution – predator/prey
relationships
Adaptive Radiation