Sounds like you're suggesting that instead of doing a headcount for population growth, we should be looking at biomass. Interesting. This would mace sense for big mac economics and the newly founded field of coke economics.
It makes sense when you think about it. Measuring things at the level of an individual implies some sort of "consciousness", but we're learning in neuroscience/philosophy class that consciousness is mostly an illusion. I mean, our brains are made of meat. How can meat be conscious?