Theories of Evolution

Evolutionary theories began emerging in the 1800’s as new geological and biological discoveries reformed existing knowledge

  • Previously, the dominant paradigm had described the ‘fixity’ of species – immutable and unchanging (man was always man)


  • Jean-Baptiste Lamarck, a French scientist, proposed that species changed as a result of the habitual use or disuse of a feature
  • Excessive use would cause a feature to develop, while continued disuse would cause it to atrophy (similar to muscle growth)
  • Lamarck proposed that these modified features could be passed on to successive generations, changing the species over time
  • Lamarck’s theory however was essentially flawed – cutting the tail off a rat does not produce tail-less offspring

Lamarck’s Theory of Evolution (Use and Disuse)

lamarck theory


  • Charles Darwin’s theory of evolution was based on a combination of Lamarckian ideas and recent fossil discoveries
  • He theorised that species living today had been changed over time and stemmed from a single (or few) ancestral organisms
  • He noted that although populations have the capacity to grow uncontrollably, limiting natural factors will restrict this growth
  • Organisms which possess traits better suited to conditions would have an adaptive advantage and be more likely to reproduce
  • These traits would hence become more common within the population and the species would gradually change over time
  • Similar ideas were proposed at the same time by Alfred Wallace (he corresponded with Darwin but published separately)

Darwin’s Theory of Evolution (Natural Selection)

darwin theory

Neo Darwinism

  • Darwin knew very little about the mechanisms of variation (i.e. mutations) or the biological basis for inheritance (i.e. meiosis)
  • Neo-Darwinism is the synthesis of Darwinian theory and modern genetics – it combines:
    • The works of Gregor Mendel in describing how traits are inherited (Mendelian inheritance)
    • The works of James Watson and Francis Crick in elucidating the genetic basis of inheritance (DNA structure)