The Dominant Animal

Human Evolution and the Environment

Protected: Chapter 6. Perception, Evolution, and Beliefs

Chapter Summary

Human beings individually evolve culturally in response to their environments, but not every aspect of their environments. People filter the information they receive from their senses in various ways. Individuals who were blind from birth, then have their sight restored as adults, are unable to process visual information normally. Similarly, if we were suddenly able to receive input from electromagnetic radiation beyond the normal human range, or from all local radio and TV signals, we would find that very disturbing. Yet, if we had grown up with that ability from infancy, our brains would have “learned” to interpret it and later would miss it if it were removed.

The human nervous system has evolved to receive only a fraction of the possible stimuli that exist, and it differs from those of other animals in several respects. Thanks to our evolutionary history of living in trees, for instance, we have stereoscopic color vision. Yet compared with that of dogs, our perception of odors and sounds is very poor. Even more removed from human experience, bats find their way about by echoes, and some fish use electric fields, although all of them lack some of our perceptual abilities.

Our perceptions are thus an interaction between the external world and the evolved characteristics of our nervous systems. Human beings, however, can compensate to some degree for our perceptual limitations through microscopes, telescopes, radio and TV, and instruments for chemical analysis, among many other devices. The evolution of our large pattern-seeking and planning brains has enabled us to expand both our physical and perceptual abilities far beyond those of other animals.

The brain itself helps to determine what we see, as can be demonstrated by trying to read while moving your head or while tapping the corner of one closed eye. Your brain receives information from sensory receptors that inform it about body position and movement. Thus it can compensate for the head movements but not the taps. The brain also is programmed to see what we expect to see. Tests of people using an “Ames room,” which from a certain angle of view seems normal but whose shape is in fact distorted, show that they perceive two average-sized people in the room as a giant and a midget. Various other optical illusions have been invented to test perceptions and how the brain organizes the information it receives. It is thought that this organizing ability is partly genetically determined and activated by an individual’s early visual experience. Two special abilities of humans, which appear to be tied to our social evolution, are good face recognition and an ability to read the emotions of others.

Although human beings share a common genetic endowment in perceptual abilities, what is actually perceived by individuals is strongly influenced by their cultural environment, and that in turn influences the course of cultural evolution. Part of one’s cultural environment is learning, which also affects perceptions. Culture-specific differences in perception become evident when individuals from a culture that does not use two-dimensional pictures to represent three-dimensional scenes are asked to interpret perspective, relative sizes, and optical illusions in pictures.

Some aspects of the human perceptual system suggest reasons that humanity seems to have such difficulty dealing with environmental problems. One is the tendency to hold the environmental backdrop constant; another is habituation—the removal of a constant stimulus from awareness (e.g., the hum of an air conditioner). Our nervous systems have filters and “feature detectors” that suppress some stimuli (steady sounds of no importance) and make us especially sensitive to others (a baby’s cry). Habituation makes it easier to notice new threats or opportunities, an ability that was of paramount importance to our evolving ancestors, and one that is still valuable in modern life. But detecting slow changes in the environment would not have been useful to our prehistoric ancestors, who had no way to influence them, so our perceptual systems evolved to ignore them.

Today, however, it is precisely such slow, deleterious changes in the background that are among the most serious threats to our future: population growth, climate change resulting from emissions of greenhouse gases, loss of biodiversity, land degradation, environmental accumulation of hormone-mimicking chemicals, and so forth. Most such changes are difficult or impossible to recognize except with the aid of specialized instruments. Thus information about gradual changes over decades can be presented in graphs or other forms that we can perceive, making it possible for society to take them into account and try to change the course of cultural evolution—a process of “conscious evolution.”

Regardless of one’s perceptions, each human being establishes a belief system—a set of beliefs about the world. The concept of cause and effect, which is seen in many animals, appears to develop very early in young humans and seems built into our nervous systems. Early humans probably wondered about many things in their everyday experience for which causes were not obvious. Lacking answers, they invented belief systems that included supernatural agents acting as causes. Many such agents were clearly modeled on people themselves, and human motives and behavior were attributed to them.

Increasing brain power and imagination among evolving humans may have led to the invention of causes of inexplicable effects, such as death, to reduce the anxiety they aroused. Experiences such as are encountered in dreams and hallucinations may be the original source of many ancient myths, legends, and ideas such as separation of mind and body. Belief in mind-body separation could easily give rise to the idea of a soul that could exist apart from one’s body. If people could have souls, then why couldn’t trees, rocks, or other natural objects? Belief in many supernatural forces or beings would naturally lead to attempts to manipulate them, as many religious groups have done through prayer, rituals, offerings, sacrifice, and the like, to achieve desired results.

Although we have very little evidence of the religious beliefs and practices of early humans, we can infer some things. Neanderthals buried some of their dead, and they may have been the first to do so. Yet there is no evidence that they included articles or decorations in burials, as Homo sapiens often did. Neanderthals evidently felt a need to protect the remains of group members, but whether there was religious significance to it is unknown. Evidence rather clearly suggests, though, there was a religious significance in burials for our ancestors at least since the great leap forward. Some religious beliefs from very early times appear to have survived in modern religions.

The roles of religion, probably from the beginning, have been, first, explanatory and manipulative—attempts to explain mysterious phenomena and to influence them—and, second, integrative and controlling—organizing groups to deal with mysterious phenomena, dictating appropriate behavior, and justifying the power of certain individuals over others. Why people invented gods in their own image is evident; why so many still profess religions when most causes of once-mysterious effects have been uncovered is less clear. Partly it may be because of persisting questions and a need for solace. Explaining the existence of evil despite belief in a loving God is not easy, yet the idea seems to have some intrinsic appeal.

Science also embodies counterintuitive beliefs and ideas, and perhaps scientists could profitably explore the appeal. The appeal of some religions may be in the structure and rules they impose, giving their adherents a sense of security. Religions also offer a basis for ethics, which science lacks. Myths, beliefs, and religions are important elements in cultures and at some level motivate everyone. If we are to resolve our environmental dilemmas, we will need to attend to the difficulties of perceiving slow deleterious changes, how belief systems influence those perceptions, and how cultures will evolve to meet the challenges.

One consequence of being predominantly a sight animal is the important role skin color has played in people’s beliefs about and treatment of others. Each human individual is unique, a result of the interplay among genes, environment, and culture; yet our categorizing brains tend to sort others and ourselves by race, religion, gender, nationality, and so forth, often including value judgments about the categories. A persistent myth is that human beings can be divided into discrete biological units called races, based on skin color and hair forms.

Hominins evolving in Africa 1.5 million years ago probably lost their apelike body hair, exposing their skin to the tropical sun while helping to develop an effective temperature-regulating system for a warm climate. Skin color then became a balance between the need to synthesize folate (a vitamin essential for reproduction that is easily destroyed by exposure to UV radiation) and vitamin D (needed for building strong bones and a healthy immune system). The former favors dark skin where sunlight is strong, as in Africa; the latter favors lighter skin where sunlight is weaker, as in northern Europe and North America. Early Homo sapiens in Africa were doubtless dark-skinned, but after some groups migrated to more northerly regions, evolution would have produced lighter-skinned people there. Geographic variation in skin color, however, is not matched by the distribution of other traits, such as hair form, height, head shape, or blood type. Thus, while “races” based on arbitrarily chosen traits may have political or social significance, they don’t exist as biological units.

Socially, though, race is real, as is racism, based on visible physical differences among people that resulted from biological evolution as well as cultural differences such as language and religion. Different groups are no longer separated geographically, and both cultural mixing and interbreeding of people of different origins have become widespread. Racism may have arisen from a need to maintain cohesion of small groups, but it has led to discrimination and justification for exploitation of out-groups. Similar discrimination has also been applied to people of different religions, gender, or ethnic origin. Extreme cases in history include slavery, the Holocaust, and the genocide in Rwanda.

Cultural evolution in many places has slowly changed racist attitudes and behavior in recent decades. In the United States, segregation and lynchings of African Americans were common in the 1930s and 1940s, but much changed after World War II through administrative and court decisions, and protests. Other forms of discrimination persist, such as reactions to Middle Eastern people following terrorist attacks and the opposition to gay marriage.

As the human population grows and is increasingly globalized and threatened, a series of ethical dilemmas present themselves. We believe that human beings have an ethical imperative to discuss and make collective decisions about the world’s future. But it will be essential to overcome our prejudicial tendencies so that we can work together to solve our human dilemma.

Key Terms

  • Carcinogens
  • Conscious evolution
  • Electromagnetic radiation
  • Face recognition
  • Feature detectors
  • Folate
  • Genital mutilation
  • Genocide
  • Gestalt laws
  • Habituation
  • Holocaust
  • Hormone-mimicking chemicals
  • Melanin
  • Nervous system
  • Neurotransmitter
  • Optical illusion
  • Race
  • Stimuli
  • Temperature-regulating system
  • Theodicies
  • Ultraviolet radiation
  • Vitamin D

Discussion Questions

  1. Explain the concept of habituation and give some examples from your everyday life.
  2. How might the characteristics of human perceptual systems have influenced the evolution of religions?
  3. What is some of the evidence that there isn’t a one-to-one correspondence between what’s “out there” and what we perceive? What are some of the implications of that fact?
  4. What role do personal and cultural expectations appear to play in how we see visual illusions?