Genetic Evidence for Unequal Effective Population Sizes of Human Females and Males
Level 4 - case-series / case-control
Level 4 by design analogy (observational cross-sectional population genetic study in non-clinical evolutionary biology)
OpenAlex W2149751230 · doi:10.1093/molbev/msh214
What was done
The authors evaluated whether differences in time to the most recent common ancestor (TMRCA) between mitochondrial DNA (mtDNA) and the nonrecombining portion of the Y chromosome (NRY) stem from natural selection or sex-biased demographic processes. They surveyed variation across 782 base pairs of the mitochondrial cytochrome c oxidase subunit 3 gene and 26.5 kb of noncoding NRY DNA from 73 individuals across three distinct groups: 25 Khoisan, 24 Mongolians, and 24 Papua New Guineans. Coalescent models were applied to estimate locus- and population-specific demographic trajectories and TMRCAs.
What was found
Across all three populations, mtDNA demonstrated an approximately twofold deeper coalescence than the NRY. In the Khoisan, estimated TMRCAs were 176.5 thousand years ago (kya) for mtDNA and 73.6 kya for the NRY. In the non-African populations, TMRCAs averaged 92.8 kya for mtDNA and 47.7 kya for the NRY. Both loci fit a constant population size model across all populations, with the exception of Mongolian mtDNA, which fit a rapid population growth model. The authors found no evidence for differential natural selection and concluded the disparity is most consistent with higher female effective population size.
Why it matters
This study provides within-population genetic evidence that the disparity between human mitochondrial and Y-chromosome coalescence times is primarily driven by sex-biased demographic history rather than selective sweeps on the Y chromosome.
Limits
The sample is limited to 73 individuals from only three populations. The sequence data cover only a single 782 bp mitochondrial gene segment and 26.5 kb of noncoding Y-chromosome DNA, without whole-genome or autosomal controls to assess locus-specific stochastic variation.
Cited by
- context Historically across human evolutionary history, only approximately 40% of men have reproduced, compared to 80% of women.