Human intestines are held in place by membranes called mesenteries. In bipedal humans, it would be logical for these mesenteries to be attached to the rib cage. Instead, they are attached to the backbone, as they are in quadrupedal mammals. Because of this arrangement, human mesenteries have a tendency to tear more often than mesenteries in other mammals, as frequently observed among truck drivers and jackhammer operators. The same evolutionary modification that causes increased susceptibility to torn mesenteries is responsible for
