Intraspecific variation
• Variation accounted for by individual, age,
and sex differences seen within every
biological species
Interspecific variation
• Variation representing differences between
reproductively isolated groups
Fossil Genera and the evolution of homo
• A genus is a group of species composed of
members more closely related to each other
than to species from any other genus.
• Ex: dogs belong to the Canidae genus that
includes wolves, jackals, coyotes and foxes
• We (and all the other extinct “Homo”s ie
Hohabilis, Homo erectus) belong to the
Genus Homo
• Species that are members of the same genus
share the same broad adaptive zone.
• Members of the same genus should all share
derived characters not seen in members of
other genera.
Ancestral and Derived (Modified) Characters
• Derived (Modified) Characters that are modified
from the ancestral condition and thus are
diagnostic of particular evolutionary lineages.
•Ancestral
•Characters
inherited by a
group of
organisms from
a remote
ancestor
Homologies
• More forelimb
similarities. These
ancestral
characteristics are
called Homologies
Generalized and Specialized
Characteristics
• Refer to the adaptive
potential of a particular trait
• Generalized if a trait is
adapted for many functions:
a mammalian limb with five
fairly flexible digits, adapted
for many possible functions
• Specialized if a trait is limited
to a narrow set of functions:
hand or foot suited for
specialized function of stable
weight support in an upright
posture
Principles of Classification
• The field that establishes the rules of
classification is taxonomy.
• Organisms are classified first on the basis of
physical similarities.
• Basic physical similarities must reflect
evolutionary descent in order for them to be
useful.
Principles of Classification
• Homologies
• Similarities based on a
common ancestor.
• Analogies
• Superficial similarities
that are a product of
separate evolutionary
responses to roughly
similar functional
demands.
• Homoplasy
• The process that leads to
Analogies.
Constructing Classifications and Interpreting
Evolutionary Relationships
• Evolutionary systematics
• A traditional approach in which presumed ancestors and
descendants are traced in time by analysis of
homologous characters.
• Cladistics
• Attempts to make rigorous evolutionary interpretations
based solely on analysis of certain types of homologous
characters (those considered to be derived characters).
Cladogram
• A chart showing
evolutionary relationships as
determined by cladistic
analysis.
• It’s based solely on
interpretation of shared
derived characters.
• It contains no time
component and does not
imply ancestor-descendant
relationships.
Birds?
Shared Derived
• Relating to specific character traits shared in common between two
life-forms and considered the most useful for making evolutionary
interpretations.
• The presence of feathers in the proposed relationship between some
(theropod) dinosaurs and birds is an example
Archaeopteryx Late
Jurssaic Period
~150mya
Clade -- car example
• From a common ancestor
of all passenger vehicles,
the first major divergence is
between cars and trucks (I).
• A later divergence occurs
between luxury cars and
sports cars (II).
• Derived features of each
grouping appear after its
divergence from other
groups.
Clade – car example
• In this “tree,” SUVs diverge
from trucks, but like sports
cars, have a decorative
racing stripe.
• This is a homoplasy and
does not make SUVs sports
cars.
• Classifications based on
one characteristic that can
appear in different groups
can lead to an incorrect
conclusion.
Evolutionary systematics
• Traditional approach to
interpreting evolutionary
relationships with the goal
of producing
classifications.
Phylogenetic Tree
• A chart showing
evolutionary
relationships as
determined by
evolutionary
systematics.
• It contains a time
component and implies
ancestor descendant
relationships.
Evolutionary systematics + cladistics
• Revised view, common ancestry of birds and dinosaurs.
Tempos and Modes of Evolutionary
Change
• Macroevolution is the change from one species to another
• Macroevolution is only partly understandable through
microevolutionary models.
• There are TWO main theories regarding Macroevolution…
Missing link? -- The Theory of
Gradualism
•
Gradualism refers to change accumulating gradually in evolving lineages, or a
series of forms with finely graded transitional differences between ancestor
and descendant, with “missing links” present
Punctuated Equilibrium
•
•
Punctuated equilibrium refers to no missing links, with real gaps representing
uneven, nongradual process of long stasis and quick spurts
These “quick spurts” still take A LOT of time, some 10,000-50,000 years.
Evolution…classified
• Organizes diversity into
categories and, at the same time,
indicates evolutionary
relationships.
• The kingdom Animalia includes
20 major phyla (singular, phylum)
• Chordata is one phyla and
includes all animals with a nerve
cord, gill slits and supporting cord
along the back.
Mammalian Evolution
•
•
The Cenozoic era, the Age of
Mammals.
ADAPTIVE RADIATION
•
•
A process that takes place
when a life form rapidly
takes advantage of the
many newly available
ecological niches.
A species, or group of
species, will diverge into
as many variations as two
factors allow:
1. Its adaptive potential.
2. The adaptive
opportunities of the
available niches
Mammalian Evolution
• Characteristics:
• The enlargement of the cerebrum, especially the
neocortex, which controls higher brain functions,
resulting in more nerve cells\
Mammalian Evolution
Monotremes
• Characteristics:
• A longer, more intense period of growth in utero
Marsupials
Placental Mammals
Mammalian Evolution
• Characteristics:
• Distinctive
dentition, termed a
heterodont
dentition, with 3
incisors, 1 canine, 4
premolars, and 3
molars in each
quarter of mouth
Mammalian Evolution
• Characteristics:
• Maintenance of constant internal body temperature,
warm-bloodedness, and ENDOTHERMIC
Ectothermic
Mammalian evolution
• Lateral view of the brain in fishes, reptiles, and
primates.
• Note the increased size of the cerebral cortex
of the primate brain.