It seems that we can piece together different "slices" of a human to arrive at a composite based on knowledge of a few variables.

 

For instance a thick neck would be correlated with a stocky well-built individual and conversely a thin neck with a slender asthenic body structure.

 

This is no coincidence.

 

Even height, posture, gait etc seems to be correlated.

 

Is this true? And if so, why?

 

Gene expression of a set of genes seems to be correlated to the overall phenotype.

 

Please advise.

 

Thanks in advance.

 

Because the body is a system and each portion develops at a rate comparable with other parts of the body. When bones develop and are much longer the muscles must also become longer to have their origin and insertion points, and conversely shorter stature means less length the muscle must have to function. This means that for the same absolute amount of muscle one of shorter stature will probably have more muscle per unit area. There's also the different types of muscle and a number of other factors, but I think that gets at what you're asking.