CLASSIFICATION OF LIVING THINGS Chapter 18
How many species are there? About 1.8 million species have been given scientific names Nearly 2/3 of which are insects 99% of all known animal species are smaller than bumble bees 99% of all species that have ever existed are now extinct
Taxonomy Classification the grouping of objects based on similarities Taxonomy the science of describing, naming, and classifying organisms Organisms are grouped into taxa (plural) or a taxon. Each category is a taxon. Freshmen (Class of 2016) Sophomore (Class of 2015) Junior (Class of 2014) Senior (Class of 2013)
History of Classification Aristotle (384 322 BCE) developed the first classification system Based on easily observable characteristics All organisms were classified as plants or animals. Plants herbs, shrubs, and trees Animals things that swim, things that fly, or things that walk.
Carl Linnaeus (1701 1778) Wrote a book Systema Naturae in 1735 that outlined his classification and naming system Classification hierarchy (groups within groups) Binomial nomenclature Organisms are grouped based on similarities in their form and structure at different levels
Levels of the Modern Linnaean System DOMAIN KINGDOM PHYLUM Gets more specific as you move down. CLASS ORDER FAMILY GENUS SPECIES And, organisms are more closely related.
Binomial Nomenclature Binomial Nomenclature a two-word naming system using the genus and species names No two species can have the same scientific name Both names are in Latin Both names are italicized (underlined if handwritten) The genus name is capitalized and the species name is lowercase The species name is an identifier or descriptor EXAMPLE Apis mellifera mellifera honey
Try these Canis familiaris Canis lupis
Try these Felis domesticus Sus domesticus
How are living things classified? Traditionally, organisms were classified based physical characteristics (what could be seen). Mammals have hair, produce milk and provide care for young, and most have live birth
Problems with the Old Way Some organisms have similar features but are not closely related Example Birds, bats, and bugs all have wings that are used to fly but each evolved separately.
Problems with the Old Way Some organisms look different but are closely related Birds are dinosaurs (reptiles)
The Missing Link (or at least one of them) Archaeopteryx
Modern Classification Based on phylogeny Phylogeny the ancestral/evolutionary relationships among species Each species has a family tree that includes many ancestors and descendents and thousands of generations. Phylogenetic tree
How is phylogeny determined? Phylogenetics uses the presence or absence of traits to determine relatedness Morphology studying the physical structure or anatomy of organisms Very traditional but useful for living species and fossils
Homologous, Analogous, or Vestigial Homologous structures traits inherited from a common ancestor May or may not have the same function or the exact same appearance Example: forelimbs of tetrapods
Homologous, Analogous, or Vestigial Analogous structures structures with common functions Example Birds, bats, and bugs all have wings that are used to fly but each evolved separately.
Homologous, Analogous, or Vestigial Vestigial Structures evolutionary leftover Example the human appendix has no apparent function while rats and other rodents have an appendix that aids in digestion Example whales and snakes have a pelvis and femur
How is phylogeny determined? Biochemical comparing DNA, RNA, and protein sequences. Genes pass from generation to generation; therefore, all descendents will have the similar DNA The more similar the DNA or protein sequence the more closely related the species
Levels of the Modern Linnaean System DOMAIN KINGDOM PHYLUM Gets more specific as you move down. CLASS ORDER FAMILY GENUS SPECIES And, organisms are more closely related.
Cladistics Cladisitics a method of analysis that infers phylogenies by careful comparisons of shared traits. Used to select the most likely phylogeny among a given set of organisms. Comparing traits Shared traits are defined as ancestral Derived traits evolve in one group but not another
Constructing a Cladogram Cladogram a phylogenetic tree that is drawn in a specific way to show evolutionary relationships Clade Clade all groups that originate from a certain point and have one common ancestor Outgroup a group that lacks some of the shared characters
New species Scientists are discovering new species all the time. So we have to know where to classify them and how to name them. http://blogs.discovermagazine.com/loom/2010/06/30/what-if-anything-is-big-bird/
Constructing a Cladogram Characters in Vertebrates Four legs Backbone Amniotic egg Hair Lizard yes yes yes No Tuna no yes no No Frog yes yes no No Cat yes yes yes Yes
Interpreting Cladograms
Cladogram Questions After which animals did mammary glands develop? What animals do not have jaws? Which animals share the trait for lungs? Which animals have derived traits that protect them from the elements (weather)? Why is the trait for feathers marked on the line for pigeons not the main line? Which animals are probably predators?