Bipedalism

The list of typical human-specific phenotypes should never be considered as a welter. In contrast, it is really important to identify their appearance time and how they interacted with each other as an adaptive strategy in human evolution.

Bipedalism is the first human-specific phenotype in the evolution of hominin species. According to the analysis of some footprint fossils left by Australopithecus, this species had already learned to walked without their forelegs. This event occurred about 3.6 MYA as a result of the changing in skeletal structure (especially in pelvis). Although there is no evidence to support that Australopithecus was small enough to produce tools by their hands, bipedalism is still a great progress it could made in its evolution because bipedalism is the premise of all latter evolution. Only by liberating its forelegs can this species make and use complexed tools in hunting, and therefore, expand the food source to support the development of its brain.

The second milestone is the use of stone implements as well as the significant rapid expansion of brain sizes. It happened 2.5 MYA when habilis lived. This coincidence may prove the hypothesis above, that the use of advanced tools can provide more food for the potential brain sizes expansion. This is also the beginning
The life-history of modern human is so different from the other extant apes such as chimpanzee. For example, human has childhood and adolescent before their mature. This should be an adaptive strategy for the expanded and energetically costly brains.The right-handedness shared by both Homo sapiens and neanderthalensis might be a result of the changing in the sensory regions of the forebrain. Nevertheless, it is still not clear whether homo habilis and homo erectus had the same feature. The origin of the human-specific facial expressions is yet in mystery due to the lack of fossil