Linnaeus's Classification and Evolutionary Relationships in Taxonomy

1. Chapter Six People’s Place in Nature

2. Linnaeus’s Classification • The science of classifying organisms into different categories is known as taxonomy. • The most significant early attempt at taxonomy was by Linnaeus. • This system is the basis of the classification system used in modern biology. • The basic unit of classification is the species. • 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.

3. The Taxonomic Hierarchy • Taxa above the level of genus are referred to as the higher taxa. • There are five main higher taxa • Family • Order • Class • Phylum • Kingdom • A family contains similar-appearing genera, • Order is group of similar- appearing families, and so on. [Refer to Table 6-1: Classification of Homo sapiens]

4. Determining Evolutionary Relationships • The development of classifications depends on knowledge of evolutionary relationships among taxa. • A comparison between two animals may reveal many anatomical correspondences. • Structural correspondences that are the result of inheritance from a common ancestor are known as homologies or homologous features.

5. Determining Evolutionary Relationships • Structures that are similar in two species, without being due to inheritance from a common ancestor, are said to be homoplastic. • Homoplasy can develop in four different ways: • Parallelism • Convergence • Analogy • Chance

6. Cladistics • In cladistics, homologies that appeared recently and are shared by a relatively small group of closely related taxa are called shared derived features. • Homologies that first appeared long ago and are shared by a larger group of species are called shared ancestral features. • Uniquely derived features are particular to a specific species within a group of species.

7. People and the Animal World • Animals must obtain their nutrients from consuming other organisms. • Animals are composed of specialized kinds of cells. • They are highly mobile and have contracting fibers, such as muscles. • Most respond quickly to changes in their environment. • The animal kingdom is divided into several units known as phyla, with each phylum representing a basic body plan. • Humans belong to the phylum Chordata. • A distinctive feature of the chordates is the presence of an internal skeleton and a notochord and nerve cord that run along the back of the animal. All chordates also have gill slits at some time in their life history.

8. The Vertebrates • The phylum Chordata includes the subphylum Vertebrata, which is comprised of most animals in the phylum. • In place of a notochord, a true vertebral column, or spine, has developed. • A major event in vertebrate evolution was the evolution of jaws. • The ancestors of land vertebrates were freshwater bony fish capable of coping with drought conditions. • These vertebrates had lungs for supplementing their oxygen supply. • The origin of land vertebrates also depended on the evolution of limbs.

9. The Mammals • Mammals are homeothermic and can control their body temperature through physiological means. • Hair or fur provides a layer of insulation. • Mammals are characterized by heterodont dentition and have two sets of teeth, deciduous and permanent. • The reptilian jaw is composed of six bones, while the mammalian lower jaw is composed of only two bones, often fused into a single structure. • Other anatomical features aid mammals in dealing with terrestrial habitats. • These characteristics include the diaphragm, hard palate, and the four-chambered heart.

10. The Mammals • Offspring develop inside the mother. • Newborn mammals are nourished by taking milk from their mother’s mammary glands. • Care is given to the young by the mother and often by the father and other adults. • Much of mammalian behavior is learned. • Mammals are characterized by improvements in the nervous system and elaboration of the brain. • Mammals are divided into prototherian mammals (the monotremes who lay eggs) and therian mammals. • Therian mammals are divided into marsupial and placental mammals.