One of the more interesting takeaways from this book that I learned was the necessity of water for life. There are organisms that can basically live in all types of conditions, such as those without oxygen that use hydrogen and carbon dioxide instead, but all organisms require water to grow and reproduce. It was fascinating to me that the question of ‘is there life on other planets’ is more a question of ‘where are there places with water’?
Another highlight was the keen observation that humans are better adapted to dry heat than humid heat. We see that humans have a large number of sweat glands which help with heat loss along with the slim and long anatomy and relative hairlessness. This is in parallel with fossil evidence suggesting that Homo sapiens originated in the hot plains of Africa.
A major misconception that was cleared up for me was the oxygen versus carbon dioxide regulation for breathing. Carbon dioxide is actually what controls breathing. When out of breathe, it is not because you need to breathe in more oxygen but rather to reduce the rising carbon dioxide concentration in the blood. This mechanism suggests that humans evolved at sea-level since the amount of oxygen in the lungs is much greater than needed when at sea-level.