I think the answer is control of the heart and lungs but i might be wrong
In a human heart there are four chambers. The deoxygenerated blood from different parts of the body firstly comes to ulper right chamber then it goes to lower right chamber and from here it goes to lungs for oxygeneration.
It's because people are around their families more than their friends and also they are related to you by blood which is why you should always be connected to them.
Muscle to fat may be the answer