Erik Trinkaus argues that fossil evidence shows signs of considerable interbreeding of Neandertals and modern humans. However, I don’t believe that proves we could have Neandertal ancestors. Couldn’t crossbreeding result in sterile offspring, such as is seen in mules?

Anne Wittke
Flagstaff, Ariz.

Sure. Trinkaus argues, however, that the presence of Neandertal traits on the skeletons of Stone Age Homo sapiens reflects the fertility of hybrid offspring .–B. Bower