  Despite its historical and biological stability, the sex ratio at birth (SRB)
has risen in parts of the world in the last several decades. The resultant
demographic consequences, mostly on sex imbalance, are well documented,
typically including "missing girls/women" and "marriage squeeze." However, the
SRB-induced impact on demographic dynamics, particularly its underlying
mechanism, has not been explored in depth. We aim to investigate the impact of
the SRB rise on the size, structure, and growth of a population, particularly
emphasizing on population aging. We provide a simple framework, derived from
classical stable population models, to analyze how the SRB rise can reduce the
population size and make the population old. We demonstrate that the cohorts
born with a higher SRB are smaller in size than those with a lower SRB. As the
affected cohorts are born into the population, their smaller size will reduce
the total population size, thereby lifting the fraction of old people that were
born with the original SRB and have the same size as before. The resultant
population aging speed increases as the cohorts with the new SRB take an
increasing share of the population. This study adds that, in addition to
fertility and mortality, the SRB can be a driving factor of population
dynamics, especially when it moves far above normal biological levels.
