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• Fossils are remains of ancient organisms trapped in rocks, tar pits, frozen in ice or embedded in amber. The activities and behavior of ancient life forms also left behind fossil traces (such as footprints, dungs, gastric stones, nests and burrows) which scientists can study.
• The records found in the rocks show a gradual evolutionary descent from simpler to more complex life forms. Paleontologists use the fossils found in rocks to track the evolutionary history of many organisms.
• Homologous structures


  Structures with the same set of bones that presumably evolved from a common ancestor. They appear different and may have varied functions.
• Analogous structures


  Structures that perform the same function but have very different embryological development or set of structures like bones.
• Vestigial structures


  Structures or attributes that have lost most of its ancestral function in more recent species.
• Wisdom teeth are vestigial third molars that most people are very familiar with. Evolutionists believed that our ancestors used these teeth to grind up the hard seeds and nuts that were once part of the human diet.
• Common structures are shared in the embryo stage and disappear by the time the embryo reaches the juvenile or adult form.

  
• Many organisms have similar molecules of life (RNA, DNA, proteins) that suggest descent from a common ancestor with modifications.
• The near universality of the genetic code reflects an evidence of common ancestry and relatedness and can be inferred from the similarities in the DNA sequences between and among organisms.

  
• Organisms usually arise in areas where similar forms already exist. Similar organisms may also be found in different locations which could mean that the two places were previously connected.
• Living things share some biomolecules which may be used to prove relationships. These chemicals include DNA and proteins. The building blocks of these chemicals may be analyzed to show similarities and differences among organisms. The more similarities, the closer the relationships.
• One of the major tasks of systematics is to determine by means of comparison what the unique properties of each species and higher taxon are. Another is to determine what properties certain taxa have in common and the biological causes of the differences or shared characters. In this way, one begins to understand the relatedness and relationships of organisms in the tree of life.

  
• Systematics has been used to construct the evolutionary relationship of life's diverse forms. In recent years, we have gained insight into the very deepest branches of the tree of life through molecular systematics.

  
• Systematics


  The study of the kinds and diversity of organisms and of any and all relationships among them. Tracing phylogeny is one of the goals of systematics; hence, it is considered as the study of biological diversity in an evolutionary context.

  
• Lines of evidence to infer evolutionary relationships


  • Fossil evidence
  • Homologies
  • Embryology/Developmental biology
  • Biogeography
  • Molecular clocks
• Hierarchical classification can reflect the branching patterns of phylogenetic trees.

  
• Systematics


  Connecting classification to phylogeny
• Phylogeny


  The evolutionary history of a species or a group of related species
• Classification


  Method of grouping organisms; arranging entities into some type of order to provide a system for cataloguing and expressing relationships between these entities

  
• Hierarchy


  A system of organizing groups into ranks according to status; putting groups at various levels according to importance or power
• Nomenclature


  The formal naming of taxa according to some standardized system
• Identification


  The process of associating an unknown taxon with a known one
• Description


  The assignment of features or attributes (characters) to a taxon
• Carolus Linnaeus realized: 'All the real knowledge we have depends on the method by which we distinguish the similar from the dissimilar. The greater the number of natural distinctions we make, the clearer becomes our idea of things...from here Linnaeus set himself the task of devising a method to: "join the similar to the similar, and to separate the dissimilar from the dissimilar in nature"
• The taxonomic system was devised by Carolus Linnaeus (1707-1778). It is a hierarchical system since organisms are grouped into ever more inclusive categories from species up to kingdom. In 1981, a category higher than a kingdom, called domain, was proposed by Carl Woese.

  
• Binomial nomenclature


  Nomenclature refers to the practice of assigning scientific names. Binomial comes from the words "bi" meaning "two" and "nomen" meaning "name". A species name consists of two parts: the genus or generic name and the specific epithet.
• Dichotomous key


  A tool that helps identify unknown organisms to some taxonomic level (e.g., species, genus, family, etc.). The key is constructed in such a way that a series of choices is made that leads the user to the correct identity of a sample organism.
• Cladistics


  Studies relationships between taxa using shared derived characters. The basic assumption behind cladistics is that members of a group share a common recent ancestor and are thus more "closely related" to one another than they are to other groups of organisms.

  
• Phylogeny


  The evolutionary relationships among organisms
• Cladogram


  A phylogenetic tree that shows relationship of taxa based on shared derived characters

  
• Character


  Any trait of an organism that can be described or measured
• Character state


  Describes the character. A particular character can have several character states.
• Homologous characters


  Characters having similar structures because these were derived from a common ancestor
• Analogous characters


  Characters that have separate evolutionary origins, but are superficially similar because they perform the same function. Analogous characters are the result of convergent evolution.
• Clade


  A group of taxa consisting of an ancestor and all of its descendant taxa
• Similarities among existing organisms (including morphological, developmental, and molecular similarities) reflect common ancestry and provide evidence for evolution.
• Biologists use phylogenetic trees to illustrate evolutionary relationships among organisms. Constructing a phylogenetic tree is one way to visualize evolutionary relatedness.

  
• Phylogenetic systematics emphasizes descent and common ancestry in order to determine the evolutionary history of groups of organisms as a determining factor in classification.

  
• To build phylogenetic trees, scientists must collect character information that allows them to make evolutionary connections between organisms. Using morphologic and molecular data, scientists work to identify homologous characteristics and genes.

  
• Family trees can be used to see ancestral connections and that all the people in the last generation have the same great-great-grandparents in common