Though historically lightly populated, political Arabia is noted for a high population growth rate - as the result of both very strong inflows of migrant labor as well as sustained high birth rates. The population tends to be relatively young and heavily skewed gender ratio dominated by males. In many states, the number of South Asians exceeds that of the local citizenry. The four smallest states (by area), which have their entire coastlines on the Persian Gulf, exhibit the world's most extreme population growth, roughly tripling every 20 years. In 2014, the estimated population of the Arabian Peninsula was 77,983,936 (including expatriates). The Arabian Peninsula is known for having one of the most uneven adult sex ratios in the world with females in some regions (especially the east) constituting only a quarter of vicenarians and tricenarians.