I believe it's true that genetics can determine body shape within certain inherited physically limiting parameters such as height, arm length, torso proportions etc. However, there are many manifestations and variations which are possible within that genetic mold. If the parents are athletic, unco-ordinated or overweight, all of their offspring are not genetically destined to the same fate. There is a lot of individual choice involved--siblings who start out pretty similar in mold, often end up looking very different based on lifestyle priorities that are very often governed by sociotype. Enneagram also likely plays a determining role, as different types exhibit differing motivations--such as pleasing others, measuring up, adhering to gender roles, asserting dominance, satiating sensory desires etc.

In the same way that IQ capacity can also to some extent be genetically passed down, it is just as common to see 2 academically over-achieving parents produce a child who just either isn't, or else chooses not to be academically focused. Just as we can predict likely careers according to sociotype as opposed to basing them on the genetically granted IQ capacity of the parents, we can assume that over time certain values will predispose certain sociotypes to exhibit certain types of bodies. Why does my sensor ESE ski, run and skate faster and more fluidly than his identical ILI brother, when that is exactly what socionics would predict. We can assume they were granted genetically comparable nervous systems and muscle twitch fibre capacity--given that they were at one time one "being". The physical differences that they DO end up exhibiting, must be due to how their sociotypes manifest in their life choices and development. The ESE is already much more bodily aware and focused, which governs his eating and grooming habits, the way he carries himself, and the fact that he engages in sports solely to maintain his health and socialize. The ILI wants to "climb the social ladder"--which at this point in his life means making the hockey Rep Team; later he could change focus towards more job-related success and therefore easily start neglecting his body.

What is intriguing is how twins from the same being or "egg/sperm combo" develop "Conflicting" sociotypes. I believe it's commonly accepted that two Alphas do not produce only Alphas. So how is sociotype determined? What would also be interesting is to type Olympic medalists in each sport to see whether physical endurance is more likely attributable to a certain quadra or informational element, gracefulness another, speed another etc.
@Hotel Transylvania - to me he looks like a 70-year-old man trapped in an 11-year-old body. ILIs can manifest and exhibit wisdom beyond their years..and yet still manage to retain an endearing element of childish naïveté.