Natural selection reduced diversity on human y chromosomes.
Level 5 - mechanism / opinion, no new human data
Computational population genetic modeling and comparative sequence analysis without clinical or interventional human data
PubMed 24415951 · doi:10.1371/journal.pgen.1004064
What was done
Genome-wide comparative analyses across X, Y, autosomal, and mitochondrial DNA were evaluated alongside population genetic simulations to test whether low diversity on the human Y chromosome is explained by neutral demographic processes (such as higher variance in male offspring count) or by natural selection acting on linked neutral variation.
What was found
The abstract reports no numerical values, effect sizes, or parameter estimates. Qualitatively, observed Y chromosome diversity was inconsistent with a purely neutral model. Models incorporating purifying selection accounted for the observed low diversity. The estimated number of sites under purifying selection exceeded the total number of Y-linked protein-coding sites, pointing to selection in ampliconic regions. The analysis could not exclude positive selection on beneficial mutations as an additional contributor.
Why it matters
This work indicates that natural selection, rather than neutral demography alone, is a primary driver of reduced human Y chromosome diversity, highlighting functional constraints within repetitive ampliconic regions.
Limits
The abstract provides no sample sizes, dataset sources, or specific numeric estimates. The analysis relies on population genetic simulations and modeling rather than direct functional experimental validation, and it cannot definitively separate the relative contributions of purifying versus positive selection.