BioConcepts

gradualismGradualismus (ger.)

• The evolution of new species by gradual accumulation of small genetic changes over long periods of time; also: a theory or model of evolution emphasizing this. (Merriam Webster 2011)
  
  category phylogenesis

  1946

  In biological evolution both acute and gradual change occur, and both may contribute to progress. The sudden extinction at the close of the Secondary Era (sudden in the geological sense) of some three-quarters of the main lines of reptilian evolution, together with the relegation to unimportance of all the remainder save the one branch of lizards and snakes – this, with the almost explosive evolution of the mammals which followed upon it, was an acute process, a revolutionary event. But the slow transformation, during perhaps fifty million years of the Secondary Era, of one small and insignificant reptilian line into a primitive mammal, and the subsequent slow transformation during another fifty million years of the Tertiary of one mammalian line into ancestral man – that was a process of extreme gradualism, to be followed once more by the acute revolutionary process of the extinction or reduction of most mammalian lines and the explosive spread of modern man. In such cases both acute and gradual processes have co-operated in progressive evolution; and it may well be that this co-operation between the violent and the gradual is inevitable in the biological sector.

  Huxley, J. (1946). A re-definition of progress [Address at the Sorbonne, 9 December 1946, on the occasion of the first session of the General Conference of UNESCO]. In: New Bottles for New Wine, London 1957, 18-40: 35.

  1960

  gradualism as preached by Lyell

  Young, K. (1960). Biostratigraphy and the new paleontology. J. Paleontol. 34, 347-358: 347.