We’ve been hearing a lot about society’s inequality in terms of wealth and income recently. Many statistics are quoted along the lines of “Britain’s top 1% own as much as the bottom 55%.

This made me think back to my DPhil work, where one of the key factoids constantly in my mind was the disproportionately demanding nature of the brain in terms of energy consumption. While it only occupies 1.5% of the mass of the body, the brain consumes ~20% of the body’s energy.

How equally does the body distribute its energy consumption? We can use data from Rolfe & Brown (1997) who describe the percentage of O2 consumption of various organs and their proportional weight. Below I replot the data in a slightly different way to make it look like an income distribution plot*. The area of each box represents the % O2 consumed, the width of the bar is the proportion of the body’s mass, so the height represents the energy usage per unit of mass, for that tissue type.

We can see that the body allocates its energy expenditure in a very unequal fashion. We can see that while skeletal muscle consumes a large 20% of O2, there is a lot of it (42% of the mass of the body) the amount of energy consumed for each gram of skeletal muscle is tiny in proportion to a gram of heart or brain tissue. The heart is the highest consumer, requiring 11% of O2 despite it consisting of only 0.4% of the mass of the body. Close behind is the brain, consuming 20% of O2 while forming only 1.5% of the body’s mass.

Does this mean we should take inspiration from biology and mimic this unequal distribution of income in society? No**.

References

Rolfe, D. F., & Brown, G. C. (1997). Cellular energy utilization and molecular origin of standard metabolic rate in mammals. Physiol. Rev., 77(3), 731–758.

* It could well be that someone has already plotted the data in this way, but I’m not aware of it so far.

** If you are a 1%’er then I may be willing to sell my soul and support high levels of income inequality in exchange for funding my professorship.