As mammals evolved, the larynx accrued added importance in new activities such as effectuating intra-abdominal pressure control during the transition from egg-laying to birthing and control of intrathoracic stabilization as movement of the upper limb required rib stabilization during climbing. The proper development of the larynx during the embryonic period is crucial to its later normal function. The permanent intersection of the respiratory and digestive pathways has created a de novo aerodigestive tract; a first of its kind in mammals. The lowered position of the human larynx has provided a greatly expanded supralaryngeal portion of the pharynx.