It is observed that the human population keep increasing significantly and it began to increase noticeably around 10,000 years ago.The greatest factor of this increase is the rapid development of the agricultures in lands, as well as the domestication of animals. These are the reasons why population increases at that time.
You're correct because when birds hit their max altitude it's harder to breathe and to minimize the time of there flight they store immense amounts of oxygen in their lungs.
