218–1 Finding Order in Diversity Life on Earth has been changing for more than 3.5 billion years1.5 million species namedbetween 2 and 100 million additional species have yet to be discovered
3Why Classify?organize living things into groups that have biological meaningTaxonomy = discipline of classifying organisms and assigning each organism a universally accepted name
4Assigning Scientific Names Common names are confusing and vary among languages or even regionsEx: cougar, mountain lion, panther, pumadifferent species sometimes share a single common nameEx: buzzard: hawk? Vulture?Scientists have agreed to a single name for each speciesUse Latin & Greek
5Binomial Nomenclature Carolus Linnaeus,a Swedish botanist, 1700sbinomial nomenclature = classification system in which each species is assigned a two-part scientific namewritten in italicsfirst word is capitalized, the second word is lower case
6Scientific Names grizzly bear is called Ursus arctos Ursus — is the genusGenus = group of closely related speciesarctos – is the speciesunique to each species within the genusOften a Latinized description of some important trait of the organism or an indication of where the organism livesUrsus maritimus, the polar bearmaritimus, referring to the sea
8Linnaeus's System of Classification Hierarchical - it consists of levelsincludes seven levelsfrom smallest to largest—species, genus, family, order, class, phylum, and kingdom.Each level is called a taxon or taxonomic category
11Humans Kingdom = Animalia Phylum (Division for plants) = Chordata Class = MammaliaOrder = PrimatesFamily = HominidaeGenus = Homospecies = sapiens
12Taxonomic groups above the level of species are “invented” by researchers who decide how to distinguish between one genus, family, or phylum, and another.
13Phylogeny = the study of evolutionary relationships among organisms Biologists now group organisms into categories that represent lines of evolutionary descent, or phylogeny, not just physical similarities.
14evolutionary classification = method of grouping organisms together according to their evolutionary history
15The higher the level of the taxon, the farther back in time is the common ancestor of all the organisms in the taxon.
16Cladogram = diagram that shows the evolutionary relationships among a group of organisms
20The genes of many organisms show important similarities at the molecular level. Similarities in DNA can be used to help determine classification and evolutionary relationships.The more similar the DNA sequences of two species, the more recently they shared a common ancestor, and the more closely they are related in evolutionary terms.
21Dichotomous KeyA dichotomous key is a tool that allows the user to determine the identity of items in the natural world, such as trees, wildflowers, mammals, reptiles, rocks, and fish.Keys consist of a series of choices that lead the user to the correct name of a given item."Dichotomous" means "divided into two parts". Therefore, dichotomous keys always give two choices in each step.