Diane Sawyer will switch from AM to PM in January when she leaves ABC's Good Morning America and takes the reigns of the networks' flagship World News Tonight from a retiring Charlie Gibson.  Sawyer joins an elite club of traditional network news anchors that includes Katie Couric at the CBS Evening News and Brian Williams at NBC nightly News.  Once an all male bastion the network nightly newscasts have changed dramatically in the past decade as ratings have declined owing to changing viewing habits and 24/7 cable news channels. 
Washington Post
TV Week