Chapter 7: The History of Life, Systematics, and Phylogeny
- Page ID
- 92826
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- Discuss the need for a comprehensive classification system
- List the different levels of the taxonomic classification system
- Describe how systematics and taxonomy relate to phylogeny
- Discuss the components and purpose of a phylogenetic tree
- Compare homologous and analogous traits
- Discuss the purpose of cladistics
- Describe maximum parsimony
- Identify the web and ring models of phylogenetic relationships and describe how they differ from the original phylogenetic tree concept
- 7.1: Introduction
- This bee and Echinacea flower could not look more different, yet they are related, as are all living organisms on Earth.
- 7.2: Deep Time
- Evolutionary changes coincide with geologic changes on the earth. Consider that changes in geology (e.g., mountain formation or lowering of the sea level) cause changes in climate and together these alter the habitats available for life. Two types of geologic change seem to have had especially dramatic effects on life: continental drift and the impact of asteroids.
- 7.3: Origins of Life
- To account for the origin of life on our earth requires solving several problems: how the organic molecules that define life (for example, amino acids and nucleotides) were created, how these were assembled into macromolecules (for example, proteins and nucleic acids) in a process requiring catalysts, how these were able to reproduce themselves, and how they were assembled into a system delimited from its surroundings (i.e., a cell). Several hypotheses address each of these problems.
- 7.4: Evidence for Early Life
- Prokaryotic organisms were the first living things on earth and still inhabit every environment, no matter how extreme. Prokaryotes are well adapted to living in all types of conditions, including extreme ones, and some prefer to live in colonies called biofilms. Archaea are believed to have evolved from gram-positive bacteria and can occupy more extreme environments.
- 7.5: Eukaryotic Origins
- Living things fall into three large Domains: Archaea, Bacteria, and Eukarya. The first two are prokaryotic and the third contains all eukaryotes. A relatively sparse fossil record is available to help discern what the first members of each of these lineages looked like, so it is possible that all the events that led to the last common ancestor of extant eukaryotes will remain unknown. However, comparative biology of currently living organisms and the fossil record provides insight.
- 7.6: Systematics and Classification
- Scientists continually obtain new information that helps to understand the evolutionary history of life on Earth. Part of this information includes relationships between organisms. While phylogeny represents the full understanding of evolutionary relationships, scientists also classify organisms into groups to use a common framework of language for all species known as binomial nomenclature.
- 7.7: Phylogeny and Cladistics
- Scientists collect information that allows them to make evolutionary connections between organisms. Similar to detective work, scientists must use evidence to uncover the facts. In the case of phylogeny, evolutionary investigations focus on two types of evidence: morphologic (form and function) and genetic.
Contributors and Attributions
Connie Rye (East Mississippi Community College), Robert Wise (University of Wisconsin, Oshkosh), Vladimir Jurukovski (Suffolk County Community College), Jean DeSaix (University of North Carolina at Chapel Hill), Jung Choi (Georgia Institute of Technology), Yael Avissar (Rhode Island College) among other contributing authors. Original content by OpenStax (CC BY 4.0; Download for free at http://cnx.org/contents/185cbf87-c72...f21b5eabd@9.87).