What are the causes of the Spartan population crisis starting in the fifth century BC?

Question

The population of the citizen caste of the ancient Greek city-state of Sparta fell dramatically starting in the fifth century BC. It never recovered until reformer kings of the third century BC began to enfranchise non-Spartiates. Why did this shortfall occur?

Answer 1

A terrible earthquake localized in the city of Sparta in the 460s BC caused massive destruction of houses and public buildings. This killed a great number of Spartiates. Normal populations tend to recover, but the Spartiates did not. This cannot have only been due to war losses in the fifth century BC. Part of the problem was that wealth had concentrated into few hands, despite the Spartiate belief in equality. Another problem was the Spartiate refusal to enfranchise non-Spartiates. Another was the high-capital system of education, by which Spartiate youths were given an education so expensive that only one or two sons per family were produced; often one or both died in war. A demographic factor involved was also the high status of Spartiate women, which correlates with low rates of reproduction in many demographic regimes.