 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 . 
