Nadia's heart rate is faster than mine on average, I may know why now:
Veritasium did an interesting study on this and this is my summary and reflection.
The smaller the mammals, the faster their heart rates and shorter their lifespans; vice versa for larger mammals, according to statistics.
For humans however, the exception to this apparent rule began around 1850, when science and modern sanitation improved, and tripled our life expectancy to 3 billion heartbeats.
Metabolic Rate = Metabolic need = the baseline amount of energy (calories) an organism requires to stay alive and keep its body functioning properly (pumping blood, breathing, cellular upkeep, brain function, temperature regulation) over a given period.
The guesses in this scaling has been debated between the Surface Law, 2/3 scaling, thus Metabolic Rate or need = M2/3) and Kleiber's Law (3/4 scaling, M3/4), and Kleiber's Law seems to hold for now.
Surface law's 2/3 scaling comes from three-dimensional Volume (Mass, M), i.e. scales with radius cubed (r3) in relation to a two-dimensional surface, i.e. scales with radius squared (r2). Surface area is thus proportional to Mass to the 2/3 power.
Kleiber found that the empirical data seems to align more with a 3/4 power scaling, in 1932. No one knew why until WBE Theory finally provided in 1997 the theoretical derivation, proving that the 3/4 exponent is the mathematical result of resources moving through a fractal, space-filling network of blood vessels.
The reason smaller mammals have faster heart rates comes down to a fundamental physical problem: they lose heat incredibly fast.
Because of the geometry of size, a small mammal has a huge amount of skin (surface area) relative to its tiny body mass (volume).
No wonder Nadia gets cold so quickly than I do. Because she has a smaller body mass, she has a higher surface-area-to-volume ratio than you do. Also men's muscle factor (more muscle mass = more metabolic resting heat) has advantage over women's. This also explain her side of the bed is so hot.
On the slightly different note: I'm going to have her cutback coffee (calming the nerves that's amped up by adrenaline triggered by caffeine which does cause hand tremor) by gradually switching to herbal tea instead of quitting cold turkey. And also hand muscle training on a stress ball.
On other notes: Uses of Scaling Laws in Cities
The concepts of scaling also apply to human cities based on their populations [02:58]:
- Sublinear Scaling (0.85 Exponent): Infrastructure like roads, electrical cables, and gas stations scale efficiently [27:19]. Doubling a city's size requires only about 74% more gas stations, making cities remarkably "green" due to shared resources [27:03, 27:36].
- Superlinear Scaling (1.15 Exponent): Socioeconomic factors scale at an accelerated rate [27:42]. Doubling a city's population yields a 120% increase in total wages, wealth, and innovation (patents) [27:42]. However, negative traits like crime and disease also increase by that same 120% margin [25:53, 26:15].