Intraspecific variation Variation accounted for by individual, age, and sex differences seen within every biological species.

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

• Characteristics:• A longer, more intense period of growth in utero

MarsupialsMarsupials

MonotremesMonotremes

Placental MammalsPlacental 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.