"My triglycerides are at 220 mg/dL" is not a useful signal to a hominid banging rocks together.
Instead, what we got was the budget version, keyed for resolution rather than understanding: thirst (osmolality of plasma fluid), suffocation (blood acidity induced by excess CO2), and when all else fails, at least vague malaise as a catch-all "something's off, let's maybe sit down."
> One thing that definitely should be within the realm of conscious control: body fat. There are ways of forcing the body to metabolize fat for energy and the biggest problem is managing excess heart (easily becomes lethal). But this could be super useful in cold climates.
Non-shivering thermogenesis is primarily mediated by brown fat. It's how babies keep warm. Adults still retain some brown fat, and it appears spending time in the cold can stimulate its production. https://stagetestdomain3.nih.gov/news-events/nih-research-ma...
> Imagine being able to literally burn body fat for heat? Nowadays most of us could probably afford the otherwise superfluous expenditure of body fat.
Brown fat is burned in the body by a protein called thermogenin (UCP1). The same process can be stimulated by the drug 2,4-Dinitrophenol (DNP), albeit to lethal consequences if you're not careful. I suppose the reason we can't do this at will is because our body can do it unconsciously for us better and more safely than our frontal cortex ever could.
Which, being the budget option, has a failure scenario: When low oxygen occurs without high CO2, people feel fine... until it's too late and they fall over, unconscious.
This can occur in enclosed spaces like caves where some other gas-mix has excluded the oxygen, or when someone hyperventilates before holding their breath.
> This chemoreceptor patent-proposal is kicking my ass. Hundley won't let me down until it's done. Hardly worth filing for, in my opinion. Who wants to smell the difference between xenon and radon?
-- Complaining Versalife employee, Deus Ex (2000)