Definitions of "evolution"

     The word evolution has many usages.  Even when only biological evolution is meant, there are many various processes, any or all of which may be meant.  Clear communication (whether you are the writer / speaker or the reader / listener) requires awareness of and attention to these various meanings, to minimize ambiguity and patent misunderstanding.  In creationism, the concept is considerably muddled by the addition of several extra concepts that have no place in scientific usage.

     Ridley devotes the first sections of his book (Chapter 1, sections 1.1 and 1.2, pp. 3-5) to an extended definition.

Note that Darwin used the word "evolved" only once in his Origin of Species, where it was the very last word of the text.  He did not even once use the word "evolution".

The Oxford English Dictionary (the standard reference for word usage in the English language) includes 12 different definitions for "evolution", including:

• Unfolding, opening out, emergence.
• Growth according to inherent tendencies.
• Rise or origination of anything by natural development.
• "The process of developing, or working out in detail, what is implicitly or potentially contained in an idea or principle."
• Biological development (i.e. ontogeny),
  (specifically, the "Theory of Evolution" by Bonnet, 1762, now referred to as "preformation").
• Formation of the heavenly bodies
• Origin of species

In Biological Evolution, casual use of the word "evolution" can mean many different things, including:

• Descent with Modification
  (or change over time; anagenesis).
• Origin of species
  (or formation of genealogical trees; phylogenesis or cladogenesis).
• Adaptation, taking place over many generations
  (note that "adaptation" also has a physiological usage, occurring within the lifespan of an individual).
• Adaptative radiation.
  (Adaptation plus cladogenesis).
• Natural selection.
• "Survival of the Fittest".
• Darwinism.
  (variation plus natural selection; also used carelessly for any aspect of biological evolution)
• Mutationism
  (the origin of species by sudden, dramatic change, also called saltationism).
• Neo-Darwinism
  (Mendelian genetics and statistical population genetics integrated with variation plus natural selection; also called the Modern Synthesis).
• Genetic drift
  (a statistical process distinct from natural selection).
• Neutralism
  (accumulation of neutral molecular changes).
• Change in allele frequencies over time
  (whether resulting from mutation, selection, or drift)
• Any of the above, in various combinations.

In many versions of "creationism", "evolution" is additionally defined as:

• Random.
• Purposeless.
• Godless.
• False.
• Associated with immorality, violence, communism, and innumerable other evils.

  Needless to say (hopefully!), these additions are gratuitous and either downright wrong or at least inappropriate when applied to the scientific subject of biological evolution.

Ridley 1.1.  "Evolution means change in living things over long periods of time."
Ridley 1.2.  "Living things show adaptation."

     In the first chapter of our text, the author tries to catch the essence of biological evolution, in its full modern usage, in a short section of several paragraphs.  Note how difficult it can be to pin down the concept with a single, brief phrase.  Here, excerpted, are some essential features from Ridley's presentation:

• "Evolution...consists of change between generations within a population lineage. ... Evolutionary modification in living things possesses some further distinctive properties.  It depends on external environmental change and on random genetic innovation... Moreover, the evolution of life has proceeded in a branching, tree-like pattern... Adaptation is another of evolutionary theory's crucial concepts... Adaptation refers to 'design' in life -- those properties of living things that enable them to survive and reproduce in nature."

     Ridley also takes pains to exclude development during the lifetime of individual organism and shifts in ecosystem composition from those changes which are to be called evolution.

NOTE that in this opening section Ridley omits any mention of heredity.  This is apparently unintentional, since he makes it plain later on that heredity is essential.  But please do realize that changes between generations are not necessarily hereditary (e.g., larger size due to improved diet) and therefore not always properly labelled as evolutionary.

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