Alаn Cооper, Cécile Mоurer Chаuviré, Geoffrey Chаmbers, Arndt von Haeseler, Allan Wilson and Svante Pääbo investigated the evolutionary relationships among some extinct and living species of flightless birds. They concluded that kiwis are more closely related to African and Australian flightless birds than they are to the moas. What new hypothesis did they propose based on this conclusion?