• Offspring are similar to parents
  • No two individuals are identical
  • Organisms can produce large numbers of offspring
  • Populations remain stable in size

Darwin concluded:

  • There is a struggle to survive
  • This is selection pressure
  • Better adapted individuals survive and pass on their genes
  • Over time a number of changes giving rise to a new species
  • Organisms in species show variation, differences in the genes
  • Those best adapted have increased chance of survival and successful reproduction
  • Repeated for many generations and so proportions of individuals with the adaptation increases
  • Repeated over multiple generations, this leads to evolution.

Darwin’s notebook