DISCOVERING OUR DISTANT ANCESTORS

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

A helpless infant requires at least one caregiving parent to survive. In other species, a newborn can fend for itself within a relatively short time, and the mother can almost immediately resume her place in the group, providing her young with food and protection. But taking care of a human infant is a full-time job. For most of human history, taking care of the infant has been the mother’s job. In subsistence societies, like hunter-gatherers, parents working together as a team were better able to get enough food than a nursing mother alone. The father can hunt for meat and bring it home to the mother, who stays close to home gathering fruits and vegetables. Human fathers take an active role in feeding their young.

Dexterity and Tool Use

Once the early humans walked, and the forelimbs were freed from their weight-bearing function, the limbs developed into hands with great dexterity, capable of more precise movements such as those needed for fashioning and using specialized tools.

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.

One mark of improved dexterity is the modification in the tools themselves. Those made by Homo erectus about 1 million years ago took 35 blows to make. The knives of Cro-Magnon, made about 20,000 years ago, were more delicately fashioned, requiring at least 250 separate blows. About 5000 BCE, human beings began to extract and use metals. This advanced technology created the need for more specialized labor. Specialization led inevitably to greater interdependence among individuals.

The Brain

Pivotal to human adaptation is our large brain, which has evolved faster than any other human organ. It took hundreds of millions of years to develop the 400 cc. brain of Australopithecus, yet in only a few million years the human brain had grown to 1250-1500 cc. and had developed the capacity for abstract thought. Our brain helped us adapt to every kind of geography and climate, and it enables us still today to transcend our biological inheritance. The brain underlies mental life: to learn, to create, to invent, to think and say things no one has ever thought. It is the largest brain, relative to body size, of all land mammals, but the size is not what matters.

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.

Language

A necessary part of human culture is language, a form of symbolic communication of external action and internal thought that has a structure of sound, gesture, meaning and logic which is similar in all other languages. It contains a classification system and allows humans to speak and think in abstractions. Thus we can plan for the future or make conjectures about something or someone not present. The subtleties of language include manipulation of others, lying, humor, gossip, insults, metaphor, and poetry.

Personhood: Self Consciousness

Another important feature is personhood, which includes a responsible self as distinguished from others that understands intentionality and the difference between right and wrong. Conflict is familiar to the groups, who have customary ways of handling it and are aware of what belongs to them and what belongs to others. They are moved by sexual attraction and at times disturbed by sexual jealousy. They know that other people have an inner life just as they do and feel emotional pain and other kinds of emotions in the same way.

Social Beings

Humans are not solitary beings but live most of our lives in groups or connected to groups of which immediate family and other kin are the most important. In addition, we have a social structure with leaders, laws, politics, division of labor, cultural norms, and religious beliefs. Our “cognitive load,” the mental capacity for managing information, appears to limit our social relationships to about 150 people, a number established by Robin Dunbar and known as “Dunbar’s number.” This is by far the largest social network of any animal, and almost three times larger than that of our nearest hominid relative, the chimpanzee.

Emotions

Human beings all over the world share the same basic emotions which are: sadness, anger, disgust, fear, surprise and happiness. Different cultural display rules, such as whether one can cry in public or show surprise or digust in different situations, account for different ways that emotions appear.

Color Vision

We all see a spectrum of colors. Most animals don’t see colors at all. Yet, color vision isn’t strictly limited to human beings, as the great apes also have it, although it isn’t clear if it is as good as ours.

Numerical Ability

While the great apes can do rudimentary counting, human beings obviously have a common number sense. In primitive societies it is limited to the concept of “1, 2 … and many”; but all human beings can learn to do mathematics, although it is difficult for some. Complex counting in primitive societies is often done by matching, for instance using stones to represent the number of domestic animals in a group at the beginning of a day and then checking the number of animals against the stones in the evening.