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Species Classification
and Macroevolution
Macroevolution
• Macroevolution is evolution on a large scale.
Changes we can see visibly as species evolve
slowly over a long period of time.
Classifying Species
• Carolus Linnaeus:
(1707-1778) Swedish
naturalist, created the
first classification of all
living creatures.
– Taxonomy
– Species
– Genus
Linnaean Taxonomy
Kingdom
• Kingdom: the most
inclusive category. All
living organisms can
be put into 1 of 5
kingdoms.
–
–
–
–
–
Plants
Animals
Fungi
Single-celled organisms
Bacteria
Kingdom
• The major differences between the 5
kingdoms are their mobility and their
sources of food.
– Example: Plants have to produce their own food
while animals must acquire and ingest food.
Phylum
• The kingdom Animalia contains about 35
phyla.
• Humans belong to the phylum Chordata.
– Chordata is a vertebrate phylum; animals which
possessed at one point in their life a notochord.
A notochord is a flexible rod that runs along the
back of the animal.
Phylum
• Humans belong to the subphylum
Vertebrata, which means animals with a
vertebral column (a backbone)
• One characteristic of vertebrates is bilateral
symmetry.
• Most vertebrates also have the same basic
skeletal structure.
– Example: a single upper arm bone and two
lower arm bones
Class
• There are 7 classes
within the phylum
Chordata.
• Humans belong to the
class Mammalia.
• Mammals evolved
from reptiles, more
than 200 million years
ago.
Order
• Humans belong in the order Primates, which
includes apes, monkeys, and prosimians.
Family and Genus
• Humans belong to the
Hominid family, the great
apes, which include
humans, gorillas,
orangutans, and
chimpanzees.
• Genus: humans belong to
the genus Homo which
includes all modern
humans and species (now
extinct) which were closely
related.
What is a Species?
• What determines how we classify species?
• Two schools of thought:
– Biological Species Concept
– Ecological Species Concept
What is a Species?
• The Biological Species Concept:
– Is defined as a group of organisms that
interbreed.
– Reproductive isolation states that members of
one group cannot successfully breed with
members outside that group.
– The ability to breed leads to gene flow in the
population.
– (Humans belong to the species Sapiens, this
includes all modern humans.)
What is a Species?
• Ecological Species Concept:
– Critics of the BSC point out that gene flow is not
necessary nor sufficient to maintain species
boundaries in every case.
– Natural selection plays an important role in
preserving the boundaries between species.
What is a species?
• Can interbreed
naturally.
• Are reproductively
isolated from other
species.
• Must produce fertile
offspring.
(Genus: one level up
from species)
• Intraspecific: refers to variation seen within
the same species.
• Interspecific: refers to variation beyond that
seen within the same species to include
additional aspects seen between two
different species.
Subspecies
• Groupings of species that
are physically distinct from
one another but are still
capable of interbreeding.
• Example: Papio
cynocephalus
cynocephalus, is 1 of 3
species of the yellow
baboon.
Reproductive Isolating Mechanisms
• The genetic isolation of a species which
causes them to be unable to produce fertile
offspring.
• Opposite of gene flow.
Reproductive Isolating Mechanisms
• Behaviors (seasonal or diurnal/nocturnal)
Reproductive Isolating Mechanisms
• Geographical
• Ecological
Reproductive Isolating Mechanisms
• Mechanical
• Sexual “courtship” behaviors
Reproductive Isolating Mechanisms
• Hybrid inviability
• Hybrid sterility
How species change
• Speciation: new species from a “parent”
species.
• Gradual change.
• Anagenesis.
• Cladogenesis.
How species change
• Anagenesis:
– “Straight-line” evolution.
– Species can gradually change over time until the
accumulation of changes becomes so great that
we label it as a different species.
How Species Change
• Cladogenesis:
– One or more new species from another
gradually over time.
– Process begins with one species and ends with
multiple species due to branching.
Speciation
• Speciation: new species from a “parent”
species.
• Reduction of gene flow followed by genetic
divergence such as mutation or natural
selection.
• At minimum outcome is two separate
species, but sometimes many new species
can form which is the result of adaptive
radiation.
• 300 closely related
cichlids species found
nowhere else.
• DNA studies show
that they arose from a
single ancestral
species.
Speciation
• Allopatric Speciation:
– When a population is divided by a barrier,
different parts of the population adapt to
different environments
Speciation
• Allopatric speciation:
– The longer the groups remain isolated the
greater the genetic difference is between the
groups.
– When the separation results in complete
reproductive isolation, a new species is formed.
– Requires a physical barrier that interrupts gene
flow and allows the two populations to
divergence by means of natural selection.
Speciation
• Parapatric speciation:
– A new species can be
formed if selection is
combined with partial
genetic isolation.
– At habitat boundaries, a
hybrid zone can be
formed.
• Hybrid zones are created
at the boundaries of
habitats, but hybrids are
not favored by selection.
Speciation
• Sympatric speciation:
– Speciation can occur even in the absence of a
physical barrier.
– Adaptive radiation occurs when a single species
diversifies to fill numerous ecological niches.
Adaptive Radiation
• Is the result of new environments or a series
of adaptations.
• With the right ecological opportunities a
group of related species can spread into a
number of niches.
Adaptive Radiation
1. When an environment doesn’t have a similar
or competing species.
2. When a large extinction rids a set of
environments of competing species.
3. When the new group of related species are
adaptively generalized (rather than
specialized) and are able to disperse
successfully into niches and displaces
species already there.
Adaptive Radiation
• Gradualism: evolutionary changes are slow but
steady over time.
• Punctuated Equilibrium: gradualism punctuated
with relatively short spurts of rapid evolutionary
change.
Extinction
• It has been estimated
that 99% of all species
that have ever existed
have become extinct.
• Mass extinction: many
species becoming
extinct at the same
time.
• Can result in
punctuated
equilibrium.
Common Misconceptions of
Evolution
• That it has directionality.
• Bigger = better.
• Natural Selection ALWAYS works.
• Taxonomy: describing
and classifying
organisms.
– Linnaeus used traits to
group organisms.
Example: Mammals: all
breath oxygen, have
hair and mammary
glands, and three
middle ear bones.
Classifying Species
• Terms used in
classification:
– Homology: classifying
based on similarities
with a common
ancestor. Typically
based on the structure
of species.
Classifying Species
• Homoplasy: evolutionary traits which are
independent but similar.
• There are two types of homoplasy:
– Convergent evolution
– Parallel evolution
Classifying Species
• Convergent Evolution:
independent evolution of
similar traits (for example
birds and flies both have
wings).
• Parallel evolution:
evolution of similar traits
in closely related species
(such as increase in dental
size in early human
ancestors)
Primitive and Derived Traits
• Primitive trait: a trait
which has not been
altered from an
ancestral state.
• Example: Fossil
evidence shows that the
first mammals had five
digits, so the fact that
humans have five fingers
and toes is a primitive
trait.
Primitive and Derived Traits
• Derived trait: a trait
which has been altered
from an earlier form.
– Horses have hooves, so
because early mammals
had five digits, a horse’s
hoof would be
considered a derived
trait.
Primitive and Derived Traits
• What is considered a primitive or derived trait is
relative.
Classification
• Two major schools of thought:
– Evolutionary Systematics: stresses the
similarities of all homologous traits (primitive or
derived) when classifying organisms into
groups.
– Cladistics: stresses evolutionary relationships
between organisms based on shared derived
traits.
Classification
• Evolutionary Systematics:
– Think of a family tree.
– First started by paleontologists in the 19th
century.
Classification
• Cladistics:
– Provides an explicit and testable hypothesis of
organisms’ relationships.
– Members of a group share a common
evolutionary history, and are "closely related,"
more so to members of the same group than to
other organisms.
– The most commonly used method to classify
organisms.
Fossils
• Formed through a process
called mineralization. This
happens slowly as water,
carrying minerals, seeps
into the small spaces
within bone.
• Traces of life forms that
include insects trapped
in tree sap, leaf
imprints, footprints,
skeletal remains.
Fossils
• Amber: fossilized tree
sap which can
sometimes contain
small animals such as
mosquitoes
Fossils
• Taphonomy: is the study of how bones and other
materials come to be buried in the earth and
preserved as fossils.