Final answer:
Gigantism is caused by an excess of growth hormone (GH), often due to the hypersecretion of GH from the pituitary gland during childhood, leading to abnormal increases in height and limb length.
Step-by-step explanation:
An excess of growth hormone (GH) causes gigantism. Gigantism is a condition resulting from the hypersecretion of GH by the pituitary gland during childhood. In such cases, children may experience abnormally rapid growth leading to very long arms and legs and a significantly taller stature than normal by adulthood. If untreated, this can result in the individual reaching heights well above the average, sometimes over eight feet. This excessive production of GH in adults can lead to a condition known as acromegaly, which is characterized by the enlargement of bones in the face, hands, and feet.