When you breathe at a constant pace, you will have a stable heart rate. The faster you breathe the faster your heart beats, which circulates more blood. More blood circulation means you will have a warmer body, that’s why when you run fast your face will get hot.
Warm blooded animals are birds and mammals, that need a constant body temperature. They are able to stay warm by the insulation of their fur and feathers. This helps them keep and regulate a constant body temperature.
Cold blooded animals are mostly reptiles, that are long and flat. They do not need a constant body temperature, but they stay warm by "basking in the sun." That is why most reptiles live in the desert, and pet lizards have heat lamps.
Eating different types of food, like fast food, will raise your blood sugar. When your blood sugar rises your pancreas sends out insulin to lower your blood sugar, this will continue until everything is back to a constant temperature. Then the insulin stops, this is a negative feedback loop.
During labor when a child presses on the cervix it sends out a signal for the body to release Oxycontin. This allows the body to start contractions until the baby is born, once the baby is born the contractions stop. This is an example of a positive feedback loop.
As evolution continues animals physical traits will start to change, but some of their internal traits won't. Like in the evolution of a human, we changed our physical appearance from a primate to a human but we are still warm-blooded mammals.