I have no idea.
Wait. I thought it was simple? Or maybe accurately modelling the energy balance of complex organisms is too complex to represent with three variables? Going back to something you said before:
People work hard to make it seem complicated and mysterious so that they have an excuse that they can tell themselves.
It think it is more the opposite. People (like you) try to make it seem much less complicated than it actually is so they can look down on and/or make fun of fat people.
You do understand that there's a continuum between eating more that you need and becoming fat and not eating enough and starving to death, right?
Yes. You postulated that:
Calories In > Calories Out + Calories Burned
explains the weight gain that has been observed in several species over the last several decades. In the example I cited, Calories In and Calories Burned are stable over time, but body weight is not. Thus, "Calories Out" is the only variable left in your formula and must therefore be responsible for the increasing body weight of the lab animals in question. I asked you to explain what it represents and why it has changed over time. If it's "pretty goddamned simple", it should be no problem for you to explain it.
The only perfect science is hind-sight.