My previous post showed how properly timed protein ingestion is crucial for building muscle. But why? Researchers may say there is a "window of opportunity," or that the body is more receptive to protein after working out. But none of this gets at the true evolutionary reasons underlying muscle growth.
The first step is to understand when our evolutionary ancestors, the hunter-gatherers, would have engaged in something resembling resistance training. My post on the Ache hunter-gatherers showed a "day in the life" of a male hunter-gatherer. The morning and early afternoon were filled with lots of walking. Later in the day, they often engaged in heated pursuit of game. They may have used weapons to bring down the game or they may have had to do it by hand. If they were successful in this, they would then butcher the meat, perhaps eat some immediately, and then bring the rest back to camp.
You can follow the chain of movements that led to a successful hunt: walking, sprinting, wrestling or throwing, butchering, and carrying. The butchering and carrying part is what could be thought of as something akin to modern resistance training. And this "resistance exercise" which taxed the muscles only took place when a hunt was successful.
From this, you can theorize that resistance exercise and a successful hunt go together. And this means that resistance exercise and the ingestion of protein and fat from meat go together. The other main food sources for hunter-gatherers were fruits and vegetables (primarily carbohydrate) and nuts (which do have a mix of carbs, protein, and fat). But the real payoff food was meat, with its large supply of protein, essential fats, and other important features such as iron and vitamin B12.
The next question is why the ingestion of protein after a successful hunt (resistance exercise) leads to muscle growth. It would be easier to understand how this would lead to the maintenance of muscle mass, but not necessarily muscle growth.
My theory is that muscle growth (mainly focusing here on men) is some sort of "indicator" of a successful hunting record. First, it takes time to build muscle. Nobody goes to the gym, eats some protein, and blows up like Popeye. It takes months of successful hunts (resistance training) and the corresponding proper nutrition (protein and fat) to build noticeable muscle.
Further, the appearance of muscle growth differentiates someone who may be fit from someone who is fit but also "brings home the goods." Let me explain. Let's say a person is cardiovascularly fit - they can run long and fast. If that is all the training they do, they will not build muscle. Muscle growth requires that a person 1) uses their muscles in the process of acquiring game (heavy loading), and 2) ingests some of the game afterwards.
Muscle growth is then a better signal of "hunting success" than is only cardiovascular training. After all, what good is it if a hunter can run fast and strong but never catches any game?
Muscle growth also weeds out "fakes" through another mechanism. And this hinges on the fact that the muscles must be utilized in order to start the process of muscle growth. This means that if a hunter somehow gets lucky (finds an already dead carcass) or cheats (steals a kill from someone else), their body will not exhibit muscle growth. This is because they did not use their muscles in the process of acquiring food, and the body does not build muscle without a physical stimulus (even if enough or even an abundance of calories is consumed). In this way, muscle growth is "honest" - it shows that a person expended effort in acquiring game and was successful.
I'm also thinking there is a feedback loop here, such that "success leads to success." Let's say that a hunter uses his muscles and acquires game. He ingests some of the protein and fat and the body builds muscle. Now this hunter is better-equipped for the next hunt since he has more muscle at his disposal.
I think this evolutionary theory of muscle growth is a very powerful and very useful framework. I will be presenting some associated evidence and implications in future posts.
