In 1869, the Newton brothers suggested that the carpal knobs may have been formed through continuous injuries, as they resemble diseased bone. It has also been claimed that the carpal knobs were instead formed due to a hereditary disease caused by inbreeding. This was dismissed in a 2013 study, since such lesions would likely not occur only in a specific part of the skeleton, but would appear in any growing bone tissue. If such a disease was due to inbreeding, it would also be present in other isolated island bird populations, but it is not. The authors instead suggested that the wing bones contained metaplastic tissue able to form the knob. This development was either in response to continuous impacts during combat, or to hormones released when individuals paired up and acquired territories. It appears a male which had long held a territory would possess especially large carpal knobs, and that their mates would have such developments as well, only smaller.