One of Darwin's aims in Origin was to demonstrate how the traditional taxonomic challenges of biological classification can be resolved if we view the natural world as the "strictly genealogical" result of descent with modification
34) All these results clearly reveal the ambiguity and uncertainty associated with the origin of species as descent with modification
from a common ancestor.
Assuming descent with modification
, characteristics are more likely to evolve only once and become passed on to descendants than the alternative, which would require traits to evolve more than once in independent lineages.
Bilica (2001) assembled and validated these and created the following evolutionary topic scales: Speciation, Diversity, Descent with Modification
, Evidence for Evolution, Natural Selection, Pace and Rate of Evolutionary Change, and Human Evolution.
Reading Malthus helped Darwin realize that differential reproduction, or what in Chapter 3 of On the Origin of Species he called the "struggle for existence," gave descent with modification
In 1859 he introduced a robust understanding of descent with modification
by means of natural selection.
Because of its ability to unite so many disparate facts and concepts, the theory of descent with modification
is considered the linchpin of biology (Dobzhansky, 1973).