Let's talk about Bergmann's rule.
It states: within closely related organisms, as latitude increases (closer to the poles), average height and volume of an organism increases.
For example, the size of penguins increases as a continuous function of latitude.
(🧑‍🎨: Karel Frydrýšek)
Named for German biologist, Karl Bergmann (1814-1865), who observed the effect exclusively in endotherms, warm-blooded animals.
We have since found similar trends in cold-blooded 'ecotherms', including marine invertebrates like copepods.
So why?
Here I need to bring in the Allen rule as well, which modifies Bergmann's: cold temperatures tend to favor shorter limbs, but larger stature.
Using the same number of cubes, you can see that shorter, thicker stacks have less surface area for their volume, which reduces heat flow.
So a round-bodied animal with stubby limbs can better maintain their heat in cold climates. Allen would predict that desert animals are smaller, but with longer, thin limbs.
Even within species, populations in colder climates tend to be more sphere-like than their desert cousins.
But I have to point out that Bergmann rule (and Allen rule) exceptions are common. It's less "law" and more "tendency".
Some of this stuff whiffs of genetic determinism when applied to human populations, like the native populations of the Arctic vs native population of the equatorial regions.
There are some alternative explanations for Bergmann's law: for example, the arctic has longer winters when food is scarce, but lower predation pressure, and cold temperatures favor longevity... all of which give benefit/opportunity for large body mass.
And it's worth noting that cold temperatures inhibit the growth of cartilage, which forms the scaffolding for new bone in the young.
Rather than a law of evolution, it could simply be environmental conditions showing their influence on anatomy without selecting for allelic variations.
For stuff like this relating to humans, it's worth pointing out to folks that homo sapiens simply haven't been around long enough for these kinds of evolutions to have happened, and are more likely the result of what characteristics are found to be attactive among various groups of humans.
Basic geometry. Surface area proportional to the square of a linear dimension; volume proportional to the cube. So the ratio of surface area to volume decreases with size.
Hold on though. Galapagos Penguins (0.95° S) are about six inches taller than Little Penguins which live as far south as Stewart Island in New Zealand (47° S).
I always thought it was that things in cold environments selected for larger bodies because the way internal heating works in life her on this planet it's more efficient when the body is bigger to a degree. There's a cut off point where it's diminishing returns.
