Crab-eating macaque findings. One of the most well known examples of experiments on crab-eating macaques is the 1981 Silver Spring monkeys case. In 2014, 21,768 crab-eating macaques were imported in the United States to be used in experimentation. The crab-eating macaque has the third-largest range of any primate species, behind only humans and rhesus macaques. The IUCN Red List categorizes the species as Least Concern, and CITES lists them as Appendix II ("not necessarily threatened with extinction", in which trade must be controlled to avoid use incompatible with their survival). A recent review of their populations suggests a need for better monitoring
Muscular evolution in humans after becoming bipedal which lengthened back muscles at the base of the tail bone and hips which in effect made them weigh more, further hampering their abilities in the trees. Early human ancestors had a tail where modern humans’ tail bone is located. This aided in balance when in the trees but lost its prominence when bipedalism was adapted. The arms also became shorter (opposite in comparison to legs) for carrying objects and using them as multi-tasking agents instead of climbing and swinging in trees. It is well known that the "Homo sapien" line of primates developed the opposable thumb