There are ten significant differences that define us as human beings.

Brain size and organization

• The fossil evidence allows us to trace the gradual increase in brain size over the past two or two and a half million years with some degree of precision.
• A large brain requires an inordinate amount of care and feeding--a diet high in protein--and exquisite temperature control in order to function properly. Increases in brain size would therefore drive changes in early human diets, because of the need to increase the intake of protein. While human species remained ominivorous, a preference for meat-eating did in fact occur over time. About 25% of our metabolism is devoted to brain function, which represents a huge investment of energy--and therefore a huge risk in terms of the overall chances for survival of the species. Overheating the large human brain in the hot climate of east Africa was potentially fatal.
• Brain organization

Erect posture and bi-pedalism

• One of the most distinctive human characteristics is our ability to walk erect (bi-pedalism). Living species of apes practice this form of locomotion occasionally--but awkwardly.
• The skull balances on top of the spinal column and the foramen magnum, the hole in the skull through which the spinal cord attaches to the brain, is centered at the bottom of the skull.
• Humans have an S-curve in their spines to support the weight of the upper body flexibly.
• The pelvic structure has been adapted to carry the stress and weight associated with bi-pedalism
• The conjunction of our thigh bones with our hip sockets has also been modified for these purposes.
• Bi-pedalism was thus a "pre-adaptation" which enabled their Hominid descendents to survive and flourish in the drier climate which prevailed after 5 million years ago and which converted forest environments into bush or open grasslands.
• Erect posture and bi-pedalism preceded the emergence of human species by several million years.
• The freeing of the hands for other tasks was a by-product of bi-pedal anatomy.
• The foot provides for a flexible platform for walking and running. Other adaptations of the foot include an extended heel, for balance, and complex arches. The foot allows the full use of our physical powers in erect walking and running, and thus frees our hands for a multitude of tasks.

The human skin as a heat diffusion device

• Humans can maintain a moderate speed of walking or running for an amazing length of time and for long distances.
• The combination of high levels of perspiration and hairlessness make our skin an efficient cooling device that dissipates the chemical heat produced by exertion.
• Prevents brain from overheating.

The hand with its uniquely opposable thumb

• The human thumb is longer than that of the chimp or gorilla and is positioned slightly more away from the plane of the other four fingers, so that thumb and fingers are "opposable."
• The thumb can be rotated against the fingers, allowing us to grasp objects both large and small efficiently. This slight anatomical adaptation creates an enormous range of functions which humans have and apes do not; it gives us both a precision and a power grip.

The face and eyes

• Our faces are adapted to the intense and complicated social lives that we live as humans; accordingly, they are "signboards" capable of sending highly complex and nuanced messages.
• Our eyes enable us to communicate subtle states of mind or emotion at quite a distance, and it is important for us to be able to "read" and interprete each other's moods, attitudes, and impending actions in this way.
• The eye-openings of human beings are much larger than the iris, the colored part of the eye. A large portion of the sclera or white part of the eye is visible.
• Our eye brows and eye-lashes are also dramatically visible
• Lip development as a means of social signaling occurred..
• Our way of life is communal and interactive to a degree rare in other creatures. Complex acts of communication--the sending and interpreting of finely shaded and suble messages--are central to our way of life.
• Forehead for bigger brain.
• Human share with other primates the ability to see in depth, in three dimensions.
• Human beings also share with primates the ability to perceive color; that is, our eyes are equipped with both rods and cones. Mammal species other than primates lack this ability and perceive the world in shades of gray.

Jaw and teeth

• The absence in humans of huge canines
• Our jaws are relatively small and unimpressive compared to those of apes. This development coincides in the fossil record with evidence of the use of fire, and raises interesting questions about the possible substitution at a fairly early date of cultural techniques for some of the basic biological functions, such as chewing tough materials to make them digestible.
• Human's unspecialized and less than robust teeth and jaws did not limit them to soft foods
• humans overcome their physical limitations with cultural techniques; our culture is, in a way, an extension of and a supplement to our anatomy. This is an important lesson from our teeth and jaws.

The throat and the position of the larynx

• The human throat has been modified to facilitate speech. We have a resonating chamber for vocal sounds about an inch and a half in length above the larynx.
• Humans can make alarge range of sounds.

The subtle forms of sexual differences or dimorphism