Phenotypic Feature (Examples) | Human Lineage Specific Trait | Possible Evolutionary Advantages |
---|---|---|
Brain growth trajectory | Prolonged postnatal brain growth and delayed myelinization period; Enhanced cognition | Allowed creation of novel solutions to survival threats, increased the critical period of learning new skills, and facilitated emergence of uniquely human cognitive skills |
Brain size | Increased brain-body size ratio; Enhanced cognition | Allowed creation of novel solutions to survival threats and improved social cognition. |
Descended Larynx | Portion of tongue resides in throat at level of pharynx. Larynx descended into throat | Helped enable spoken language |
Eccrine sweat gland density | Higher density of eccrine glands; enhanced sweating capacity | Enhanced cooling ability; protection of heat-sensitive tissues (e.g. brain) against thermal stress. Facilitated endurance running. |
Endurance running | Improved energy utilization during periods of high energy demand; Increased capacity to transfer energy (glycerol) from fat stores to muscle; Anatomical changes relating to running ability | Allowed persistence hunting to emerge as a viable strategy for accessing the benefits of increased meat consumption Increased range of food sources Improved diet may have facilitated brain evolution |
Labor | Earlier onset and longer duration of labor | Partially protected child/mother from damage due to increased head circumference |
Lacrimation | Emotional lacrimation (Crying) | Enhance emotional communication within social groups Increased affective communication |
T cell function | Relative T cell hyperreactivity | Enhanced immune function |
Thumb | Increased length, more distally placed, larger associated muscles | Created more detailed tools Manipulated objects on finer scale |