I believe it is a combination of polygenic inheritance and environmental factors. Several genes control the height in humans, giving an overall normal distribution. Environmental factors on the other hand such as nutrition smooth out the curve. It is therefore important to note that Human height is a quantitative, or metric trait, that is, a characteristic that is measured in quantity, and is controlled by multiple genes and environmental factors.
Prophase
prometaphase
metaphase
anaphase
telophase
The reason for the loss of color after the industrial revolution is that the light-colored moths were "selected against" by predators. These birds could only see the light ones against the newly dark, sooted background. Over time, these predators could no longer distinguish the dark ones from their natural dark, sooted background. Thus more light-colored moths stood out against the dark soot, and were eaten. And more dark-colored moths eluded the birds, survived to reproduce, passing on more of their dominant genes for dark color to their offspring. After several decades of hundreds of thousands of generations, most of the later generations were dark, due to selective advantage of camouflage to survive predation.
The smaller the surface area to volume ratio, The larger the Cell will become.
And the larger the cell, The ability to take in and use nutrients from its environment tend to be Decreased.
This happens because the large cells wouldn't have enough material fast enough to accommodate/fulfill its large volume.