निम्नलिखित में से किसने 'इष्टतम जनसंख्या' (Optimum Population) की अवधारणा को दर्शाने वाले सूत्र का प्रतिपादन किया था?

A large portion of the non-ecumene region of the Earth has remained sparsely populated primarily because of:

A significantly low sex ratio (fewer females per male) is most typically associated with which type of urban centers due to male-selective migration?