Muscle Hypertrophy is the scientific term for muscle growth, and this is the ultimate goal of any bodybuilder. There are thousands of theories on the net that tell you to do X number of repetitions for growth, or do this many sets of this many reps, or eat this or eat that. With so many theories out there we thought we would take a step back and look at muscle hypertrophy from a scientific and logical point of view.
For thousands of years humans had to hunt for their own meals, and once they got one, they didn't know how long it would be until their next meal became available. For this reason, our bodies will naturally go into survival mode once a meal is digested. This is why muscle will not grow naturally if it's not needed. One pound of muscle burns 6.5 calories per hour vs. fat, which burns 1.2 calories per pound per hour . Muscle burns more caloric energy than fat, and since we are constantly going into survival mode because of our genetic instincts, we have to give our bodies a good reason to produce muscle in order for it to happen. Bodybuilders do this in two ways.
How to Trick Your Muscles into Growing:
1: The first way bodybuilders trick muscles into growing is by eating multiple small meals throughout the day. This is recommended often to bodybuilders, and this actually has sound reasoning behind it. If your body is constantly bringing in small meals, it does not get a chance to switch over into survival mode. If your body is not in survival mode, it can continue to produce muscle. This is done by...
2: Lifting progressively heavier weights that are just outside of your comfort zone. Again, your body will not produce new muscle if it's lifting weight that it's already capable of lifting. Adding new muscle will burn more calories, which it will naturally avoid.
From "The Mystery of Skeletal Muscle Hypertrophy":
"Through exercise, the muscular work done against a progressively challenging overload leads to increases in muscle mass and cross-sectional area, referred to as hypertrophy." 
More muscle means that the body will burn more calories, and since this is not desirable from an evolutionary perspective, your body will resist gaining muscle unless you give it a good reason to grow. If you lift weights just outside of your natural reach you are sending signals to your body that more muscle is needed.
Our conclusion is that the human body is hard-wired to resist building muscle. To override this response, two factors are needed. You first need to eat often enough so that your body will not switch into survival mode, and second, you need to lift weights just outside of your comfort zone to give your body reason to build muscle. In other words, since muscle burns so much more caloric energy than fat, your body needs to be convinced that more muscle is needed (done by lifting progressively heavier weights) and needs to be fed often enough to stave off it's survival instinct (done by eating multiple small meals throughout the day).