Phylogeny (or phylogenesis) is the origin and Evolution of a set of organisms, usually of a Species. A major task of Systematics is to determine the ancestral relationships among known species (both living and extinct). The most commonly used methods to infer phylogenies include Cladistics, Phenetics, Maximum likelihood, and Bayesian inference. These last two depend upon a Mathematical model describing the evolution of characters observed in the species included, and are usually used for Molecular phylogeny where the characters are aligned Nucleotide or Amino acid sequences.
During the late 19th century, Ernst Haeckel's Recapitulation theory, or biogenetic law, was widely accepted. This theory was often expressed as "ontogeny recapitulates phylogeny", i.e. the development of an organism exactly mirrors the evolutionary development of the species. The early version of this hypothesis has since been rejected as being oversimplified. However, modern biology recognizes numerous connections between Ontogeny and phylogeny, explains them using evolutionary theory, and views them as supporting evidence for that theory.
| Basic topics in Evolutionary biology |
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| Processes of Evolution: evidence - Macroevolution - Microevolution - Speciation |
| Mechanisms: Selection - Genetic drift - Gene flow - Mutation |
| Modes: Anagenesis - catagenesis - Cladogenesis |
| History: History of evolutionary thought - Charles Darwin - The Origin of Species - modern evolutionary synthesis |
| Subfields: Population genetics - Ecological genetics - Human evolution - Molecular evolution - phylogenetics - Systematics - evo-devo |
| List of evolutionary biology topics | Timeline of evolution | Timeline of human evolution |