Paranthropus

According to research, one main reason for the extinction of the genus Paranthropus was quantity and lack of space. More Australopithecus took up the survivable habitats of Africa. However, if there was more area and food for them to have lived, Anthropologist said that Paranthropus would have developed into the species as smart as humans, for they had the largest brain capacity for their time. Theoretically, there would have been highly intellectual gorilla like species.

http://www.columbia.edu/itc/anthropology/v1007/2002projects/web/paranth/paranth.html

Existence of Neanderthals Supports MRE

From this article above, research has been conducted on the oldest Neanderthal skeletal fossil found in Germany, supporting the MRE theory by the neanderthals gene pool slowly decreasing as mutation occurred due to changes in diet, weather patterns, and other environmental factors. This sub species was not able to survive, yet gave production to the homo sapiens, even though some homo sapiens had never been Neanderthals. They state the reason for this was for temporary and unique evolutionary factors that turned to become obsolete after generations

http://humanorigins.si.edu/evidence/genetics/ancient-dna-and-neanderthals/neanderthal-mitochondrial-dna