Article and Chart: Interbreeding Among Hominid Species

This chart summarizes nicely the emerging complexity of interbreeding among hominids.

Article: Dmanisi Skull May Point to Diversity within a Single Species

Unique Skull Find Rebuts Theories On Species Diversity in Early Humans

While not a genetic study, the Lordkipanidze article has an interesting angle to study of the most complete ancient skull of its age, the Dmanisi skull.  The researchers point out that there is considerable diversity to shape to the various skulls found in the cave.  Some have interpreted this as evidence of different hominid species living in the same cave over time, but the researchers in this article find that the Dmanisi skulls have no greater variability than comparing the skulls of a sample of humans living today.

D. Lordkipanidze, M. S. Ponce de Leon, A. Margvelashvili, Y. Rak, G. P. Rightmire, A. Vekua, C. P. E. Zollikofer. A Complete Skull from Dmanisi, Georgia, and the Evolutionary Biology of Early Homo. Science, 2013; 342 (6156): 326 DOI: 10.1126/science.1238484 

A. Margvelashvili, C. P. E. Zollikofer, D. Lordkipanidze, T. Peltomaki, M. S. Ponce de Leon. Tooth wear and dentoalveolar remodeling are key factors of morphological variation in the Dmanisi mandibles. Proceedings of the National Academy of Sciences, 2013; DOI: 10.1073/pnas.1316052110