18-1 Finding Order in Diversity

2. 18-1 Finding Order in Diversity

3. 18-1 Finding Order in Diversity • Natural selection and other processes have led to a staggering diversity of organisms. • Biologists have identified and named about 1.5 million species so far. • They estimate that 2–100 million additional species have yet to be discovered.

4. To study the diversity of life, biologists use a classification system to name organisms and group them in a logical manner.

5. In the discipline of taxonomy, scientists classify organisms and assign each organism a universally accepted name. • When taxonomists classify organisms, they organize them into groups that have biological significance.

6. Assigning Scientific Names • Common names of organisms vary, so scientists assign one name for each species. • Because 18th century scientists understood Latin and Greek, they used those languages for scientific names. • This practice is still followed in naming new species.

7. Early Efforts at Naming Organisms • The first attempts at standard scientific names described the physical characteristics of a species in great detail. • These names were not standardized because different scientists described different characteristics.

8. Carolus Linneaus developed a naming system called binomial nomenclature. • In binomial nomenclature, each species is assigned a two-part scientific name. • The scientific name is italicized.

9. The first part of the name is the genus name (Capitalized). • A genus is a group of closely related species. • The second part of the name is the species name (lowercase). • The species name often describes an important trait or where the organism lives.

10. Linnaeus's System of Classification • Linnaeus not only named species, he also grouped them into categories.

11. Linnaeus’s seven levels of classification are—from smallest to largest— • species • genus • family • order • class • phylum • kingdom

12. Each level is called a taxon, or taxonomic category. • Species and genus are the two smallest categories. Grizzly bear Black bear

13. Genera that share many characteristics are grouped in a larger category, the family. Black bear Giant panda Grizzly bear

14. An order is a broad category composed of similar families. Grizzly bear Black bear Giant panda Red fox

15. The next larger category, the class, is composed of similar orders. Grizzly bear Black bear Giant panda Red fox Abert squirrel Class Mammalia

16. Several different classes make up a phylum. Grizzly bear Black bear Giant panda Red fox Abert squirrel Coral snake PHYLUM Chordata

17. The kingdom is the largest and most inclusive of Linnaeus's taxonomic categories. Grizzly bear Black bear Giant panda Red fox Abert squirrel Coral snake Sea star KINGDOM Animalia

18. Grizzly bear Coral snake Sea star Black bear Giant panda Red fox Abert squirrel

19. 18-2 Modern Evolutionary Classification

20. Linnaeus grouped species into larger taxa mainly according to visible similarities and differences.

21. Evolutionary Classification • Phylogeny is the study of evolutionary relationships among organisms.

22. Biologists currently group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities. • Grouping organisms based on evolutionary history is called evolutionary classification.

23. The higher the level of the taxon, the further back in time is the common ancestor of all the organisms in the taxon. • Organisms that appear very similar may not share a recent common ancestor.

24. Different Methods of Classification Mollusk Crustaceans Conical Shells Appendages Crab Barnacle Limpet Barnacle Limpet Crab Molted external skeleton Tiny free-swimming larva Segmentation CLASSIFICATION BASED ON VISIBLE SIMILARITY CLADOGRAM Active Art

25. Superficial similarities once led barnacles and limpets to be grouped together. Conical Shells Appendages Crab Barnacle Limpet

26. However, barnacles and crabs share an evolutionary ancestor that is more recent than the ancestor that barnacles and limpets share. • Barnacles and crabs are classified as crustaceans, and limpets are mollusks.

27. Many biologists now use a method called cladistic analysis. • Cladistic analysis considers only new characteristics that arise as lineages evolve ( called derived characters). • Characteristics that appear in recent parts of a lineage but not in its older members are called derived characters.

28. Derived characters can be used to construct a cladogram, a diagram that shows the evolutionary relationships among a group of organisms. • Cladograms help scientists understand how one lineage branched from another in the course of evolution.

29. A cladogram shows the evolutionary relationships between crabs, barnacles, and limpets. Crustaceans Mollusk Barnacle Limpet Crab Molted external skeleton Segmentation Tiny free-swimming larva

30. The genes of many organisms show important similarities at the molecular level. • Similarities in DNA can be used to help determine classification and evolutionary relationships.

31. DNA Evidence • DNA evidence shows evolutionary relationships of species. • The more similar the DNA of two species, the more recently they shared a common ancestor, and the more closely they are related in evolutionary terms. • The more two species have diverged from each other, the less similar their DNA is.

32. Molecular Clocks • Comparisons of DNA are used to mark the passage of evolutionary time. • A molecular clock uses DNA comparisons to estimate the length of time that two species have been evolving independently.

33. Molecular Clocks A gene in an ancestral species 2 mutations 2 mutations new mutation new mutation new mutation Species Species Species C B A

34. A molecular clock relies on mutations to mark time. • Simple mutations in DNA structure occur often. • Neutral mutations accumulate in different species at about the same rate. • Comparing sequences in two species shows how dissimilar the genes are, and shows when they shared a common ancestor.

35. 18-3 Kingdoms and Domains

36. The Tree of Life Evolves • Systems of classification adapt to new discoveries. • Linnaeus classified organisms into two kingdoms—animals and plants. • The only known differences among living things were the fundamental traits that separated animals from plants.

37. There are enough differences among organisms to make 5 kingdoms: • Monera • Protista • Fungi • Plantae • Animalia

38. Six Kingdoms • Recently, biologists recognized that Monera were composed of two distinct groups: Eubacteria and Archaebacteria.

39. The six-kingdom system of classification includes: • Eubacteria • Archaebacteria • Protista • Fungi • Plantae • Animalia

40. Changing Number of Kingdoms Names of Kingdoms Introduced 1700’s Plantae Animalia Late 1800’s Plantae Protista Animalia 1950’s Animalia Monera Protista Plantae Fungi Archae-bacteria Animalia 1990’s Eubacteria Protista Fungi Plantae

41. The Three-Domain System • Molecular analyses have given rise to the three-domain system of taxonomy that is now recognized by many scientists. • The domain is a more inclusive category than any other—larger than a kingdom.

42. The three domains are: • Eukarya, which is composed of protists, fungi, plants, and animals. • Bacteria, which corresponds to the kingdom Eubacteria (true bacteria). • Archaea, which corresponds to the kingdom Archaebacteria.

43. Modern classification is a rapidly changing science. • As new information is gained about organisms in the domains Bacteria and Archaea, they may be subdivided into additional kingdoms.

44. Domain Bacteria • Members of the domain Bacteria are unicellular prokaryotes. • Their cells have thick, rigid cell walls that surround a cell membrane. • Their cell walls contain peptidoglycan.

45. Domain Bacteria • The domain Bacteria corresponds to the kingdom Eubacteria.

46. Domain Archaea • Domain Archaea • Members of the domain Archaea are unicellular prokaryotes. • Archaea live in extreme environments. • Their cell walls lack peptidoglycan, and their cell membranes contain unusual lipids not found in any other organism.

47. Domain Archaea • The domain Archaea corresponds to the kingdom Archaebacteria.

48. Domain Eukarya • The domain Eukarya consists of organisms that have a nucleus. • Eukarya includes the kingdoms • Protista • Fungi • Plantae • Animalia

49. Domain Eukarya

50. Domain Eukarya • Protista  • The kingdom Protista is composed of eukaryotic organisms that cannot be classified as animals, plants, or fungi. • Its members display the greatest variety. • They can be unicellular or multicellular; photosynthetic or heterotrophic; and can share characteristics with plants, fungi, or animals.