Extension (or straightening) of the elbow stops when the proximal end of the ulna engages the (or straightening) of the elbow stops when the proximal end of the ulna engages the of the humeruscoronoid fossa of the humerusolecranon fossa of the humerusmedial epicondyle of the humerus

The right answer is olecranon fossa of the humerus

The humeral trochlea is limited, behind and above, by a deep excavation, the olecranon cavity or fossa, where the free extremity of the forearm extends on the arm in the extended movements of the forearm. the free end of the olecranon, in front, it is surmounted by an analogous but much smaller excavation: it is the coronoid cavity or fossa, destined to receive the coronoid process of the ulna in the movements of the forearm on the arm. The two olecranon and coronoid fossae are separated from each other by a very thin, transparent bony septum, sometimes replaced at its center by a fibrous lamina.

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genetic variation will increase because of a new habitat and food source.

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