Human
In general, humans can survive for two to eight weeks without food, depending on stored body fat. Survival without water is usually limited to three or four days. About 36 million humans die every year from causes directly or indirectly related to starvation. Childhood malnutrition is also common and contributes to the global burden of disease. However global food distribution is not even, and obesity among some human populations has increased rapidly, leading to health complications and increased mortality in some developed, and a few developing countries. Worldwide over one billion people are obese, while in the United States 35% of people are obese, leading to this being described as an "obesity epidemic." Obesity is caused by consuming more calories than are expended, so excessive weight gain is usually caused by an energy-dense diet.
Infra-Worlders
The Infra-Worlders are a society of humans led by Captain that has lived for five decades in a gigantic submarine named the "Infra-World." These humans have been "evolved" so that their bodies can withstand the water pressure at 5,000 fathoms beneath the ocean's surface; as a result, they cannot live on the surface of the world.