The body has the ability to maintain balance or homeostasis and whenever there is something that depletes, the body also compensates. When the body does not have enough intake, this results in muscle loss. What the body does to prevent this is that, it uses an alternative energy source by using KETONES.
Answer - Speciation
Reasoning - Pretty much what has happen was the two species has evolved over the course of evolution if you want to put it that way why the are incapable of breeding.
The layers above would be not as old and the layers below would be the older layers.
Answer:
Temperature
Altitude or Elevation
Moisture or water vapour.
Explanation: