Lecture 7: What is evolution?

 

September 20, 2016

 

Evolution is the process of descent with modification. Ancestors give rise to descendants that inherit ancestral features in modified form. This process of descent with modification, which has operated for more than 4 billion years of geological time, has produced the diversity of Life on Earth. These are the basic ideas of the Theory of Evolution, which underlies all aspects of modern biology.

 

Processes of evolution: Many different natural processes can shape evolutionary change, including:

  • natural selection (Darwin's favorite)

  • sexual selection

  • heterochrony

  • pliotropy

  • drift

  • Gene duplications

  • there may be many other mechanisms

 

Evolutionary Patterns:  Time, Space, and Form 

 

1) Distribution of Organisms in Time

  •    paleontology

2) Distribution of organisms in Space

  • biogeography

3) Distribution of Organismal Form

  • comparative anatomy

  • embryology

  • molecular biology

  • genetics

 

Basic Concepts and Vocabulary of Evolution and Systematics

  • Ontogeny: life-history of an individual organism like you or me.

  • Phylogeny: evolutionary history of a lineage of organism - genealogy.

  • Cladogram: a genealogical diagram depicting the phylogeny of a group of organisms; uses only monophyletic groups.

  • Monophyletic group: Consists of an ancestor and all of its descendants; cladograms depict relationships among monophyletic groups.

  • Characters: heritable attributes of organisms; we reconstruct the phylogeny of organisms by studying the distribution of their characters.

  • Synapomorphy: A kind of character: a character that was an evolutionary novelty in the ancestor of a specified group; you must know in which group a character originated for it to be considered a synapomorphy.

  • Plesiomorphy: A kind of character: a character of an organism or group that was inherited from a distant ancestor.

 

History of a Character

 

1) Characters used in systemtatics originate as an evolutionary novelty in the ancestor of a group. At that point, the character is said to be a synapomorphy of the group. For example, the vertebral column (=backbone) first appeared in the ancestral vertebrate; the vertebral column is said to be a synapomorphy of the group Vertebrata. You must know (or hypothesize) in which ancestor the character first appeared to call it a synapomorphy.

 

2) The ancestor passes the character on to its descendants, in which it is referred to as a plesiomorphy. Sharks, primates, and dinosaurs are members of Vertebrata and all possess a vertebral column. But since they simply inherited it from the ancestral vertebrate, the vertebral column is a plesiomorphic character for sharks, primates and dinosaurs.

 

     THEORY: A statement of what we hold to general laws, principles

                   or causes of something known or or observed.

    Examples: Theory of Gravitation (Newton), Theory of Relativity

                    (Einstein), Theory of Evolution (Darwin).

    Hypothesis: A premise or assertion subject to testing and

                      falsification; only after extensive testing and many

                      failures to falsify a hypothesis is it elevated to the

                      status of theory.

  

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