I'm wondering if the creationist has misunderstood the word 'fixation'. It seems like they believe it means the mutation has been 'fixed' in the sense of it being repaired, therefore, in their mind, there is no mutation anymore.
I'm wondering if the evolutionist's can just admit that there are two alleles being discussed, not two mutations. One is introduced by mutation (which as they state is random - as mutations are not a product of natural selection), and the other allele was introduced through mating, which is a product of natural selection.
Hence their later informing us that new genetic variation introduced through mating was two to three orders of magnitude greater than that introduced by mutations...
https://www.researchgate.net/publication/277516740_Grant_PR_Grant_BR_Phenotypic_and_genetic_effects_of_hybridization_on_Darwin's_finches_Evolution_48_297-316
"Morphological consequences of hybridization were studied in a group of three interbreeding species of Darwin's finches on the small Galapagos island of Daphne Major in the inclusive years 1976 to 1992. Geospiza fortis bred with G. scandens and G. fuliginosa. Although interbreeding was always rare (< 5%), sufficient samples of measurements of hybrids and backcrosses were accumulated for analysis. Five beak and body dimensions and mass were measured, and from these two synthetic (principal-component) traits were constructed. All traits were heritable in two of the interbreeding species (G. fuliginosa were too rare to be analyzed) and in the combined samples of F-1 hybrids and backcrosses to G. fortis. In agreement with expectations from a model of polygenic inheritance, hybrid and backcross classes were generally phenotypically intermediate between the breeding groups that had produced them. Hybridization increased additive genetic and environmental variances, increased heritabilities to a moderate extent, and generally strengthened phenotypic and genetic correlations. New additive genetic variance introduced by hybridization is estimated to be two to three orders of magnitude greater than that introduced by mutation. Enhanced variation facilitates directional evolutionary change, subject to constraints arising from genetic correlations between characters. The Darwin's finch data suggest that these constraints become stronger when species with similar proportions hybridize, but some become weaker when the interbreeding species have different allometries. This latter effect of hybridization, together with an enhancement of genetic variation, facilitates evolutionary change in a new direction.
Cited for this reason....
". In short, they argue that hybridization may act as a possibly more abundant source of adaptive genetic variation than mutation because mutations are rare and hybridization common. They cite Grant & Grant (1994) who estimated that the amount of new, additive genetic variance introduced by hybridization was two to three orders of magnitude higher than that introduced by mutation in Darwin's finches."
https://www.researchgate.net/publication/234156635_The_unpredictable_impact_of_hybridization
.. During this non-equilibrium phase, inter-individual variation in traits affecting dispersal becomes spatially assorted because, at each generation, the best dispersers aggregate at the expanding front, seeding new populations. Notably, inter-individual variation is an inherent property of all natural populations, with profound implications for non-equilibrium processes such as range expansion and
hybridization that have long been neglected, most often for the sake of simplicity [19]. As the expansion wave advances, the process of spatial sorting can promote rapid directional evolution of traits favoring dispersal, thus further accelerating the establishment of populations in newly colonized areas."
Mainly because most evolutionists hold views contrary to the reality when it comes to cross-breeding, as was even shown in plants...
https://www.researchgate.net/public...n_is_important_in_evolution_but_is_speciation
"This results from segregation and recombination between the parental genomes ( Arnold et al., 2012;Abbott et al., 2013). Previous studies have shown that hybrids are usually a
complex mosaic of both parental morphological characters
rather than just intermediate phenotypes, and a large proportion of first and later generation hybrids
which exhibit extreme or novel characters ( Abbott et al., 2013;Saetre, 2013). The increased morphological variability, increased number of flowers per plant, and different flower colour variations and mode of presentation, exhibited by Psoralea hybrids in our study possibly account for the observed increase in the number and types of different species of pollinators (Xylocopa and Megachile spp) contributing to the observed higher reproductive success of the hybrids in these populations."
Offspring are not simply intermediate phenotypes of the parents. It depends on the particulars of which mate....
https://www.researchgate.net/public...orphological_diversity_in_adaptive_radiations
"The process of adaptive radiation involves multiple events of speciation in short succession, associated with ecological diversification. Understanding this process requires identifying the origins of heritable phenotypic variation that allows adaptive radiation to progress. Hybridization is one source of genetic and morphological variation that may spur adaptive radiation. We experimentally explored the potential role of hybridization in facilitating the onset of adaptive radiation. We generated first- and second-generation hybrids of four species of African cichlid fish, extant relatives of the putative ancestors of the adaptive radiations of Lakes Victoria and Malawi. We compared patterns in hybrid morphological variation with the variation in the lake radiations. We show that significant fractions of the interspecific morphological variation and the major trajectories in morphospace that characterize whole radiations can be generated in second-generation hybrids. Furthermore, we show that covariation between traits is relaxed in second-generation hybrids, which may facilitate adaptive diversification. These results support the idea that hybridization can provide the heritable phenotypic diversity necessary to initiate adaptive radiation.
"
But the outcome is wholly dependent upon the genetic details of each population.. The allometric relations may weaken or tend to strengthen genetic correlations, depending on if they are similar or different... leading to new variation and differences in form....
"... This means that in a hybridization event it will matter which individuals from each population actually are involved in the hybridization. In Darwin's finches, it has been shown that when allometric relations differ between populations, genetic correlations tend to weaken, whereas when allometries are similar, genetic correlations tend to strengthen (Grant & Grant, 1994). Thus, the outcome is dependent on the genetic details of each population. ..."
Or as the Grants put it:
"The Darwin's finch data suggest that these constraints become stronger when species with similar proportions hybridize, but some become weaker when the interbreeding species have different allometries. This latter effect of hybridization, together with an enhancement of genetic variation, facilitates evolutionary change in a new direction."
Tas just doesn't want to accept that his beloved mutations take second seat to plain ole mating in creating genetic variation and adaptation, leading to new species (although I contest that conclusion - leading to new "sub-species" is the proper terminology and classification).