Charles Darwin gave his theory of evolution in his book origin of species by means of natural selection 1869 - based on following observations and inferences
observation
1. individuals multiply geometrically yet population remains roughly constant.
interference. species struggle for existence within species among species and with environment.
2. Individuals have variations in their population
natural selection acts on this variation and the fittest survive
3. the variations are hereditary and the fittest pass them on to new generations.
changes accumulate over time and species get evolved.
darwinism was a scientific theory of evolution based on solid facts and radically changed discourse on evolution.
criticism
geometric progression of population is not universal for example man and does not reproduce that fast in fact act negative rate of growth is also observed.
Darwin ignore the contribution of mutation, genetic drift, inbreeding and hybridization in evolution and too much focus on natural selection.
is theory of pangenesis for explaining heredity was wrong.
unlike his theory, many variations are not hereditary
didn't explain the origin of variation - the arrival of the fittest was not explained.
Later, his theory was molded add and upgraded to the modern synthetic theory of evolution by scholar like dobzhansky Fischer and wright.