थॉमस रॉबर्ट माल्थस ने किस वर्ष 'एन एसे ऑन द प्रिंसिपल ऑफ पॉपुलेशन' में जनसंख्या का अपना प्रसिद्ध सिद्धांत प्रतिपादित किया था?

In traditional anthropological classification of human races, which racial group was characterized as 'yellow-skinned'?

What is the approximate estimated proportion of ecumene (habitable) and non-ecumene (uninhabitable/sparsely inhabited) areas on the Earth's surface?