Human Universals: Traits All Humans Share
Human evolution has produced a remarkable set of common characteristics, which is what makes us human. Some are physical, like the skeleton for walking upright, a vocal tract for speech, and dexterity for tool use. We share a common set of emotions and the capacity for self-awareness, abstract thinking, knowing right from wrong, and doing complicated math. All are examples of the hundreds of traits shared by all human beings in the world today.
The process of human adaptation is the simultaneous development of all the following distinctly human characteristics, in a positive feedback loop. The effects of the loop have continuously increased the difference between our nearest ancestors and us.
Bipedalism: Standing Up and Walking
Human beings are bipedal—that is, we walk on two feet instead of on all fours. Chimps and gorillas can stand upright at times, but when they move they typically do so on all fours. A fossil skeleton called Lucy is the earliest ancestor found to date whose bones show that she walked on two legs. Lucy is about 3.75 million years old, about 1 million years older than the use of tools.
Bipedal walking and running enabled us to cover greater distances over time than any other animal. Almost all other animals live their lives in the environment in which they are born. Our ancestors more readily travelled into unexplored territories and thus triggered several adaptive advantages for us over other animals:
A standing animal can see farther than it can smell, so a more sophisticated visual system needed to develop along with our upright posture. Our ancestors thus were able to spot approaching danger as well as opportunities from farther away.
Hands were freed from weight-bearing responsibilities, making tool use possible.
Erect posture also led to profound changes in human sexuality and in our social systems.
Immaturity and its Consequences
With the freeing of the front limbs, the hind limbs had to adapt to bearing the entire weight of the body. The human back was not originally “designed” to support an upright posture (which partially explains why back pains are a common complaint). To support the additional weight, the human pelvis grew thicker than that of the great apes, which made the female’s birth canal, the opening through which infants are born, much smaller.
While the birth canal was becoming smaller, however, the fetus’s brain and head were growing larger. If there had been no evolutionary correction for this, the human species would have died out; the solution was to have human babies born very early in their development.
Human children have the longest infancy in the animal kingdom. They are not as competent and independent as baby chimps or baboons. Within a day, baby baboons can hold onto their mothers by themselves. The human child is helpless and will die if not cared for during the first few years of its life.
At birth a chimp’s brain is about 45 percent of its adult weight, while a human baby’s brain is 25 percent of its adult weight. This means that the major portion of the human brain’s development occurs outside the womb, and the environment plays a much greater role in it than in any other animal’s brain development. Because the environment we are borne into differs for each person, the specific abilities that each of us develops differ considerably.
The Mother-Father-Infant Relationship
Dexterity and Tool Use
Human ancestors began to make tools as early as 3 million years ago. Specialized tools for chopping, digging, killing, cooking, washing, and skinning led to specialized labor by those who used them. Some people gathered wood or nuts, others dug for roots, still others hunted and killed animals. Axes made the hunt more efficient; choppers and scrapers could be used to butcher a large animal at the kill. At home, tools helped scrape the nutritious marrow out of the bones; animal hides could be scraped to make warm clothing.
What is crucial is where the brain expanded. Although the anatomy of much of our brain is identical with that of other primates, our cerebral cortex, the uppermost part of the brain, is the largest and most elaborate of all primates. The cortex is the area of the brain associated with higher brain function. It is divided into four sections or “lobes”. The frontal lobe is associated with reasoning, planning, parts of speech, movement, emotions, and problem solving; the parietal lobe is associated with movement, orientation, recognition, perception of stimuli; the occipital lobe is concerned with visual processing and the temporal lobe with perception and recognition of auditory stimuli, memory, and speech.
Those areas of the brain that control fine motor movements (enabling nonhuman primates to swing through trees and grasp tightly onto branches) became further developed once we came down from the trees. Our early ancestors used these fine motor movement skills to make tools and to use them. And these fine movements are the same ones involved in language. The increasing size of the cerebral cortex thus gave our ancestors great advantages—from control of delicate muscle movements to the development of speech and written language.
Personhood: Self Consciousness
Carl Zimmer, New York Times
Skin pigmentation genes are shared across the globe; one of them, for example, lightens skin in both Europeans and hunter-gatherers in Botswana. The gene variants were present in humanity’s distant ancestors, even before our species evolved in Africa 300,000 years ago.
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