Points of Agreement
Natural selection
- differential reproduction; eg preferential reproductivity of organisms having one or more favourable characteristics (generally preferential survival, at least to reproductive age, but could be eg comparable longevity but enhanced reproductivity)
Natural selection is an inevitable consequence of there being variation and competition in nature.
Evolution
Species are not fixed, they can evolve through the cumulative action of natural selection on variations, e.g. gradual adaptation of a species to its environment.
Different subpopulations of a species can diverge through them acquiring (randomly and/or through the action of natural selection) different variations; this divergence can lead to the formation of new species (speciation).
There is difficulty defining species, but speciation can occur whether the definition is based primarily on degree of morphological difference or in/ability to interbreed.
Variation
Morphological variation arises through:
- mixing genes already present
- corrupting existing genes such that they are no longer viable (e.g. different eye colours in Drosophila); this can occur through changes in the protein-coding region of the relevant DNA and/or the associated control region.
Timescale
The earth is about 4.5 billion years old.