BIO102_SYSTEMATICS

• Macrotaxonomy is the branch of taxonomy that establishes rules to the classification of superior taxa
• Naturalistic systematics - naturalists sought to classify nature in a way that reflected nature, rather than the ways humans use nature
• Darwin's Theory of Natural Selection suggested that all organisms are related by descent
• Classification is the grouping of organisms often on the basis of simple observable traits
• Taxonomy - study of biological classification
• Artificial classification divides organisms by what is useful at that time
• Natural classification is based on evolutionary relationships between organisms and their evolutionary descents
• The goal of systematics is to determine the phylogeny - evolutionary history - of a species or a group of related species
• Phylogenies are inferred by identifying organismal features and characters that vary among species
• Characters can be morphological, molecular, chromosomal, and behavioral or ecological
• Homologous characters are shared characters that result from common ancestry
• Homoplasies are shared characters that are NOT a result of common ancestry, but of independent evolution
• Convergent evolution occurs when natural selection, working under similar environmental pressures, produces similar (analogous) adaptations in organisms from different evolutionary lineages
• Shared primitive character is a homologous structure that is older than the branching of a particular clade from other members of that clade
• A shared primitive character is shared more than just the taxon that is being defined
• An example of a shared primitive character is that all mammals have bones, but so do other vertebrates
• A shared derived character is a new evolutionary feature unique to a particular group
• Shared derived characters are most useful for determining evolutionary relationships
• Ancestral character state is the FORM of the character that was present in the common ancestor of the group
• Derived character state is the variations of that character that arose later
• All mammals have hair, but no other animals have hair is an example of a shared derived character
• Polarity (which version of the trait is ancestral) is determined by outgroup comparison
• An outgroup is CLOSELY RELATED, but NOT part of the group being examined (ingroup)
• Ancestral character is found in both the study group and the outgroup
• Derived character groups are found in the study group, but not the outgroup
• Clades are groups that share derived characters and form a subset within a larger group
• The unit of common evolutionary descent is a clade
• Synamorphy is a derived character that is shared by all members of the clade
• Using synamorphies to define clades will result in a nested hierarchy of clades
• Ancestral character states for a taxon are called plesiomorphic
• Symplesiomorphies are shared ancestral characters
• Symplesiomorphies do not provide useful information for forming a nested series of clades