The Right Model in the Wrong Era: Repositioning Zeng, Aw and Feldman (2018) within a Two-Regime Framework of the Y-Chromosome Bottleneck

The post-Neolithic Y-chromosome bottleneck, in which male effective population size fell to a small fraction of its former level while female effective size grew, has two candidate generators: skew imposed by female choice, and skew imposed by force. Zeng, Aw and Feldman (2018) modelled the second generator, through competition between patrilineal kin groups, and applied it to the Neolithic. This paper argues that their model is correct in mechanism and misplaced in era. Within a two-regime framework, a selection coefficient (S, choice) and a force coefficient (F, coercion, exercised through elimination strategies) generate Y-diversity collapse under distinguishable multi-ledger signatures, and Zeng et al.'s model is the elimination form of the force regime with the production layer switched off, the competing units fixed as patrilineal kin groups, and female diffusion replaced by an assumption. Its assumptions fail on every ledger in the Neolithic and hold in one later setting: the colonization of the Americas, where paternal-lineage replacement, maternal lineage loss, a spatial admixture gradient, and dated founder starbursts match the force signature. Run there, with three re-estimations, their mathematics works. The bottleneck's history is partitioned between the regimes, and Zeng et al.'s contribution belongs, intact, to the era of force.