21.   He is constructing evolutionary trees for the various human and simian viruses and one cat virus that stymie immunological processes.

22.   In a commentary accompanying the study, George Washington University anthropologist Daniel Lieberman said the discovery of the ancient skull adds to the confusion about the human evolutionary tree.

23.   In a commentary accompanying the study, George Washington University anthropologist Daniel Lieberman said the skull adds to the confusion about the human evolutionary tree.

24.   That means anthropologists may have to rethink the human evolutionary tree.

25.   They collected DNA samples from a wide variety of mammals and proceeded to construct evolutionary trees by looking at how similar the species were in five different genes.