People’s Place in Nature Chapter 6

Taxonomy The science of classifying organisms into different categories Each plant or animal is known by a binomen, or two-part name consisting of a generic and a specific name. This is the system of binomial nomenclature. For example, the binomen for humans is Homo sapiens. Taxa above the level of genus are referred to as “higher taxa” There are five major higher taxa: kingdom, phylum, class, order and family. This can be expanded by the use of prefixes and other terms, such as: suborder and superfamily

Principles of Classification A comparison between two animals may reveal many anatomical correspondences Homologies Similarities based on, and shared by, a common ancestor Analogies Similarities based on common function, with no assumed common evolutionary descent Homoplasy Separate evolutionary development of similar characteristics in different groups of organisms A characteristic shared by a set of species but not present in their common ancestor Ex: Independent eye development

Evolutionary Relationships Homoplasy can develop in four different ways: Parallelism – development of similar characteristics separately in two or more lineages of common ancestry Convergence - development of similar characteristics separately without common ancestry Analogy – Development of similar function with no common ancestry Chance – Similarity in characteristics developed completely independently

Homologies Similarities in the forelimb bones of these animals can be most easily explained by descent from a common ancestor

Cladistics Cladistics - Attempts to make rigorous evolutionary interpretations based solely on analysis of certain types of homologous characters Clade - Lineage, or a group of organisms sharing a common ancestor The group includes the common ancestor and all descendants Clades are nested, one in another, as each branch in turn splits into smaller branches

Ancestral and Derived Characteristics Can only be used when comparing two species Ancestral (Primitive) Characters inherited by a group of organisms from a remote ancestor and not diagnostic of groups that diverged after the character appeared A trait that was retained by a species from its ancestor and is shared by two organisms Derived (Modified) Characters that are modified from the ancestral condition and thus are diagnostic of particular evolutionary lineages Trait that has evolved after break off from common ancestor

An Example of Cladistic Analysis: Evolution of Cars and Trucks 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

An Example of Cladistic Analysis: Evolution of Cars and Trucks (cont’d) 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

The Chordates Animalia – Kingdom that includes 20 major phyla Chordata – the phyla which includes all animals with a nerve cord, pharyngeal slits, and supporting cord along the back Humans belong to the phylum Chordata Vertebrates - Animals with segmented, bony spinal columns Sub-phylum of Chordata In place of a notochord, a true vertebral column, or spine, has developed Includes fish, amphibians, reptiles, birds, and mammals The origin of land vertebrates also depended on the evolution of limbs

The Mammals Homoeothermic - can control their body temperature through physiological means Hair or fur provides a layer of insulation Heterodont dentition - teeth consist of different sizes and functions Incisors, canines, premolars, molars Most offspring develop inside the mother Monotremes (prototherians) – primitive mammals that lay eggs Therians – marsupial and placental mammals Mother’s mammary glands for infant feeding

Teeth Reptilian teeth (top) are homodont Mammals are heterodont, they have different kinds of teeth; incisors, canines, premolars, and molars

The Mammalian Brain Mammals are characterized by improvements in the nervous system and elaboration of the brain Most mammalian behavior is learned Can record memories that produced positive and negative reactions to experiences Leads to feelings and emotion Limbic System – Section of the mammalian brain with three main structures Hippocampus - primarily associated with memory and spatial navigation Amygdala - enter for emotions, emotional behavior, and motivation Hypothalamus – Responsible for production of hormones that control temperature regulation, thirst, hunger, sleep, mood, and sex drive