Transcript Chapter5ol4
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.