Both in his The Origin of Species, 6th ed. Darwin's inability to form a synthesis of natural selection, sexual selection, and progenesis revolves around this issue of whether variation is random, not random, or something in between. Researchers from Mivart to Steele have focussed on the fulcrum that random variation represents. Darwin was frustrated by his own efforts at the reconciliation of the two extremes represented by natural selection and progenesis. It is our belief that the problem has been one of logical levels, a common source of confusion as pointed out by Gregory Bateson in his discussions of Whitehead's theory of logical types.
Natural selection is the progenitor, the ancestor of the other selective processes.
Natural selection selected for sexual selection, uterine selection, and zygote selection. None of the products of the other three selective processes can meet the requirements of evolution unless they also pass the test of natural selection, that they survive to procreation age and procreate. Cultural selection is one additional selective process not yet alluded to in this work. Cultural selection, learning on an abstract level, is a product of female sexual selection. It lies two levels down from natural selection, but still must past muster when it comes down to an individual's survival to procreation age.