Here's an informative research paper, "Exercise and Gene Expression: Physiological Regulation of the Human Genome Through Physical Activity." The paper describes how our genes are "made" for the Stone Age and how exercise is necessary to activate certain genes.
One sentence that jumped out to me was this: "what is called the mechanisms of skeletal muscle hypertrophy from sedentary levels today would probably be the maintenance of muscle mass in the Late Palaeolithic era."
This looks at muscle hypertrophy (enlargement) from an opposite view: that hypertrophied muscles are the "normal" state, and that the modern environment with low physical demands produces an abnormal situation where most people do not have a lot of muscle mass.
Many people think the process of a person going to the gym and making their muscles larger can be viewed is an unusual one. Now research could be saying that hypertrophied muscles should be the norm. This is not say everyone should look like Arnold Schwarzenegger. Implicit in all this is that everyone has a different capacity for muscle hypertrophy, and that most of us can't blow up our muscles like a balloon. But it does perhaps say that each of us should be working and growing our muscles to the best of our ability.