Research on Ancient DNA Could Test Predictions of Non-Darwinian Speciation Models | Evolution News

Independent of each other, different groups of researchers (e.g., Hössjer et al. 2016), more or less skeptical of common ancestry, have recently suggested the alternative model of initial heterozygotic diversity. The common element in these models is the working hypothesis of a large variation of beneficial alleles in terms of heterozygosity, later transformed over time by migration, isolation, and natural and sexual selection into phenotypically different populations or descendent species.

By “heterozygotic,” what do I mean? Briefly, the following: Genes can come in different variants. These are called alleles, always present in pairs in species like ours with two parents, possessing two sets of chromosomes from mother and father respectively. In each organism the pair of genes can either have the same allele (homozygosity) or two different alleles (heterozygosity).

For example, assume a hypothetical gene for hair length. It can come in the allele L for longer hair and S for shorter hair. Organisms with the heterozygotic combination LS can have an intermediate or variable condition, or long or short hair if one of the alleles is dominant. A heterozygotic parent can pass on either allele L or allele S. Therefore, the offspring of two heterozygotic parents can have all possible combinations, either heterozygotic LS / SL or homozygotic LL or SS. The latter will usually differ significantly from the phenotype of their heterozygotic parents. Homozygotic organisms can only pass on a single allele type and thus have less information than heterozygotic parents.

The suggestion, noted above, of initial heterozygotic diversity can explain the origin of genetically different populations and descendent species from an ancestral species in relatively short time. Such a process of speciation would not be evolution in the sense of gradual successive generation of new beneficial information by mutation and selection. Instead, it would represent a process of devolution through partitioning of information that was initially set in the ancestral species. As soon as the original heterozygosity of beneficial alleles is partitioned into separated homozygotic populations, the process of further speciation would slow down or even come to a halt. Genetic decay would then accumulate through mostly neutral and detrimental mutations (Sanford 2014).

Such decay could either increase general heterozygosity or, in the case or bottlenecks and isolated subpopulations, decrease heterozygosity. Obviously, the prediction from this model is that we should find more genetic diversity of beneficial alleles in ancient populations or ancestral species of a lineage, while finding less diversity of such beneficial alleles in recent populations or descendent species. We should also find most beneficial alleles in the ancestral groups and hardly any new beneficial alleles in the descendent groups. Finally, we should find a growing percentage of detrimental alleles in successively more recent populations.

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