Nature has its upper hand and is least concerned about the narrations of human theories and philosophies. Rather it is the opposite. Nature law to run its course has little to do with obeying King or God. So the extinction of species causes when birth rates are lower than death rates. See this rule in China, India, or N2I grave-lover Pakistan, Bangladesh which are growing fast than Parsis can catch up.
Parsis are illustrious community but they are victim of the nature rule, I.e., two deaths for one birth. The Indian government is concerned about declining disciplined Parsi community because of their many valuable services to their economy and community. So the government has launched ‘Jiyo Parsi’ fertility clinics to raise their birth rates. Marrying four wives are not an option which defies the said rule.