Until more recent times, scientists named Things with crazy long names that Just described the organism. Apis pubescens, thorace subgriseo, abdomine fusco, pedibus posticis glabis, untrique margine cilatus.
Taxonomy The science of naming and classifying organisms is called taxonomy. Until the mid-1700s, biologists named a particular type of organism by adding descriptive phrases to the name of the genus
A Simpler System A simpler system for naming organisms was developed by the Swedish biologist Carl Linnaeus
Linnaeus’s two-word system for naming organisms is called binomial nomenclature Over the past 250 years since Linnaeus first used two-part binomial species names, his approach has been universally adopted
Scientific Name The unique two-part name for a species is now referred to as its scientific name The first word is the genus to which the organism belongs. A genus is a taxonomic category containing similar species
The second word in a scientific name identifies one particular kind of organism within the genus, called a species. A species is the basic biological unit in the Linnaean system of classification With Linnaeus’ system, the honey bee Is now called Apis mellifera.
Classifying Organisms Linnaeus worked out a broad system of classification for plants and animals in which an organism’s form and structure are the basis for arranging specimens in a collection The genera and species that he described were later organized into a ranked system of groups that increase in inclusiveness
Similar genera are grouped into a family Similar families are combined into an order Orders with common properties are united in a class
Classes with similar characteristics are assigned to a phylum Similar phyla are collected into a kingdom Similar kingdoms are grouped into domains
Classification of the Honeybee Each level of classification is based on characteristics shared by all the organisms it contains The honeybee’s scientific name, Apis mellifera, indicates that it belongs to the genus Apis, which is classified in the family Apidae All members of the family Apidae are bees that live either alone or in hives, as does Apis mellifera
What Is a Species? In 1942, the biologist Ernst Mayr of Harvard University proposed a biologically based definition of species, which is called the biological species concept
Mayr defined a biological species as a group of natural populations that are interbreeding or that could interbreed, and that are reproductively isolated from other such groups Sometimes individuals of different species interbreed and produce offspring called hybrids
Evaluating the Biological Species Concept The biological species concept works well for most members of the kingdom Animalia, in which strong barriers to hybridization usually exist In practice, modern biologists recognize species by studying an organism’s features
But the biological species concept fails to describe species that reproduce asexually, such as all species of bacteria and some species of protists, fungi, plants, and even some animals
Number of Species The number of species in the world is much greater than the number described Only about 1.5 million species have been described to date Scientists estimate that 5 million to 10 million more species may live in the tropics alone
Evolutionary History Classification based on similarities should reflect an organism’s phylogeny, that is, its evolutionary history Through the process called convergent evolution, similarities evolve in organisms not closely related to one another, often because the organisms live in similar habitats
Similarities that arise through convergent evolution are called analogous characters Phylogenic Diagram of Mammals
Cladistics Cladistics is a method of analysis that reconstructs phylogenies by inferring relationships based on shared characters With respect to two different groups, a character is defined as an ancestral character if it evolved in a common ancestor of both groups A derived character evolved in an ancestor of one group but not of the other
Cladistics is based on the principle that shared derived characters provide evidence that two groups are relatively closely related A biologist using cladistics constructs a branching diagram called a cladogram, which shows the evolutionary relationships among groups of organisms Organisms that share derived characters, are grouped together on the cladogram
Considering Characters The great strength of cladistics is objectivity. If a computer is fed the same set of data repeatedly, it will make exactly the same cladogram every time The disadvantage of cladistics is that the degree of difference between organisms is not considered
Cladistic analysis does not take into account variations in the “strength” of a character, such as the size or location of a fin or the effectiveness of a lung. Each character is treated equally
Evolutionary Systematics In evolutionary systematics, taxonomists give varying degrees of importance to characters and thus produce a subjective analysis of evolutionary relationships In this type of analysis, evolutionary relationships are displayed in a branching diagram called a phylogenic tree Evolutionary systematics involves the full observational power of the biologist, along with any biases he or she may have.
Evolutionary Systematics and Cladistic Taxonomy