Ibisobanuro ahagana hasi ku ipaji

a Mu gitabo uwitwa Charles Darwin yanditse, yasobanuye ko hari ingingo z’umubiri “zidafite akamaro” (The Descent of Man). Umwe mu bashyigikiraga ibitekerezo bye yavuze ko hari ingingo nyinshi z’umubiri zidafite icyo zimaze, urugero nk’ishyira hamwe n’urugingo rugira uruhare mu gukora abasirikare b’umubiri (thymus).