A heritability of body weight of 0.4 means that body weight is determined for 40% by genetic factors and for 60% by environmental factors. True or false? Solution True. This is not to say that there are no genetic factors influencing body weight, different people will have different tendencies, to be lean, or not so lean, etc. just like height and other physical features are determined by many gene variants. Even the microbiome is influenced by both genetic factors that favor some gut bacteria over other, but diet plays a huge role too. People do come in all shapes and sizes, but the environment plays a huge role..