Consilience

The borderland between the sciences and the humanities is guarded on one side by public intellectuals who claim the study of mind and awareness for artists, psychologists, and philosophers; on the other side, the border has few visits from scientists, who are too busy within their specialized departments to wonder about the border. This region needn’t be a no-man's land; instead, specialists from both sides of the gap can explore this terrain. For example, they can explore how the ongoing processes of genetic evolution and cultural change—gene-culture coevolution—affect each other. Serpent dreams, for another example, involve an epigenetic rule, or genetic predisposition, to fear snakes, a fear influenced by cultural inputs enshrined in religious practice, social ceremonies, and shared beliefs.

Human culture is handed down from one generation to the next in large part through speech. Chimpanzees, arguably the smartest nonhuman animal, share complex social systems that engage in politics, manipulation, and lying. Chimps also have cultures, for instance inventing tools and using them differently in different groups. However, they don't use language much beyond gestures and facial expressions. A human child of six, on the other hand, has a vocabulary of about 14,000 words.

The mind recalls events as episodic memory and concepts as semantic memory. A series of similar episodes gets coded in the mind as semantic nodes represented with symbols. For example, bad experiences with poison berries are soon symbolized, in the nervous system, with skull and crossbones or some similar emblem. Linked symbols create meaning: hounds, hares, and “chase” form a proposition, in this case meaning “the hunt.” Linked meanings become schemas; for example, Apollo’s courtship of Daphne is the schema of a failed hunt (Daphne escapes by turning into a laurel tree). Cultural meanings are “hierarchically arranged components of semantic memory" (148). A unit of culture is variously called an idea, concept, culturgen, or several other names, especially “meme.” A meme is a way of linking biology with communication theory.

The same genes can express different traits in different environments. The arrowleaf plant displays arrowhead-shaped leaves on dry land, lily-pad leaves on water, and eelgrass-type ribbons underwater. Within certain dietary cultures, some people become fat while others stay lean; in a different dietary environment, both groups stay lean. Later-born children tend to become more politically liberal as adults than their first-born siblings. Genes and environment combine in various ways to produce individuals with varying traits. The percentage of variation caused by genes is called heritability. For example, in a group of distance runners, studies might show that 20% of their performance is inherited and 80% is due to their environment, including training and upbringing, while the performance variation in identical twins will be almost 100% from environmental factors.

Sometimes children with natural aptitudes for certain activities—music, auto racing, and so forth—are encouraged by parents and teachers to develop those talents, causing them to become even more proficient than children with average talent. Thus, the environment augments the inherited trait. The extent to which IQ is inherited is hotly disputed in politics; both sides agree that there is at least some heritability, but they disagree on the amount. Generally accepted, though, is that cultural variation between societies is due to environmental divergence and not genetic inheritance.

Heritability is easy to research through medical genetics, where disease symptoms—the hallucinations of schizophrenia, for example—are being associated with specific genes within human DNA. By 1997, over 1,200 diseases had been linked to single genes. Single-gene defects have specific biochemical markers in the body, making tests for such diseases straightforward and cures likely. For more complex phenomena, from hair texture to human behavior, dozens of genes can be involved, vastly increasing the difficulty of locating specific genetic defects connected to, for instance, depression and manic depression.

A scholarly list from 1945 contains 67 cultural universals, including athletic sports, cooking, courtship, education, folklore, games, government, housing, language, marriage, medicine, personal names, property rights, and religious ritual. Nonhuman civilizations, such as intelligent termites, might emphasize darkness, coprophilia, caste systems, cannibalism, and skin shedding. Human civilizations that evolve in isolation tend to have the same universal traits; witness the stone-age separation of Siberians into the Western Hemisphere, where they developed societies remarkably like those that evolved in Eurasia. Though the details differ, the universals of all human societies betray a pattern of “prepared learning,” that is, skills dictated by genetic proclivities. 

Sociobiology is the study of the biological basis of human behavior—for example, the perception of sound and how it shapes speech and music, the perception of color, and the sensations of taste. Infants prefer sweet liquids, and they grimace, in specific ways that persist for life, in response to acid, salty, and bitter flavors. Animals focus on smell and taste, but in all human languages sensory words mostly refer to sight and sound. An infant only 10 minutes old, pre-wired for facial recognition, will “fixate more on normal facial designs drawn on posters than on abnormal designs" (165). Basic expressions that represent various emotions are universal across cultures. However, subtle changes in, for instance, smiling can signal nuances that vary in different cultures.

Less than one percent of the relevant genes have been identified. Many physical and mental traits depend on polygenes, or assemblages of multiple genes located on several chromosomes. Polygenes can add to or subtract from a trait, and figuring out which polygenes control what traits can be daunting. The puzzles get more complicated with pleiotropy, in which a single gene causes multiple effects. Fortunately, most polygenes contain less than 10 genes, which makes the problem more manageable.

The complete mapping and sequencing of the human genome in the early 21st century will greatly empower research and help provide answers to genetic puzzles. Among the expected finds are the genetic basis for mental disorders, gender differences, and sexual preferences. Though some such discoveries will be politically controversial, they will engage public interest and may provide scientific resolution for some of the debates.

An example of a universal cultural preference that closely reflects an inherited human sensory trait is the description of color. All languages describe colors not as a smooth continuum but as a rainbow of four basic hues. Different languages place the definitions for red, yellow, green, and blue in nearly the same places on the color spectrum. Languages contain words for as few as two and as many as 11 basic colors, and languages with more colors always add up the first seven in the same order: black, white, red, green or yellow, blue, and brown. To fully understand the human condition, then, culture and genetics must be considered together. 

Like all creatures, humans have evolved to fit their environment. They also alter the environment by developing cultures that improve human survival fitness. Cultures grow and evolve, in turn putting pressure on people, so that those who better adapt to the culture tend to increase in population, while those people who struggle with cultural demands do less well. In this respect, human behavior and the cultural environment coevolve. Gene-culture coevolution moved slowly for hundreds of thousands of years, then began to speed up by 10,000 years ago with the development of agriculture. Since then, cultural evolution has evolved much more quickly than the human genome. Cultures thus are tethered to a human speed of adaptation left over from much a slower era, sometimes dragging people along behind it: “fast-evolving cultural norms may no longer be optimally fit” (183).

Sociobiologists have discovered distinct social traits influenced by human reproduction. In kin selection, for example, a woman might give up having children and, instead, help raise the children of a sister, who shares half her genes, if together they can raise more than double the number of offspring either could rear alone. Mating strategies—courtship, mate selection, women’s coyness, and men’s promise of fidelity—arise from the burdens of pregnancy, which are unevenly shared between males and females. Status gives leaders and kings a large share of women and a disproportionate share of offspring. Territorial expansion and defense also confer resource advantages on aggressive leaders and their people; those who “defend private resources for themselves and their social group pass more genes on to the next generation" (185). Thus, warlike aggression tends to recur in most societies.

Unlike ants and bees, which are programmed to work together, humans cooperate for selfish reasons, and contractual agreement is a fundamental part of that behavior. Sociobiologists have discovered that one characteristic towers above all others in setting contracts, the skill of cheater detection. Much of human culture, including gossip, moralism, and politics, centers around how to deal with cheating. In humans, epigenetic rules are both narrow and broad: for instance, smiling is narrowly controlled, while territorial instincts are broadly channeled. The complete set of rules as yet eludes scientists; that solution awaits more developments in biology and more interdisciplinary work involving biologists, psychologists, and anthropologists.

An early success in consilience is the explanation for the universality of incest taboos. Incest results in offspring with high numbers of genetic defects and an early mortality rate twice that of outbred children; siblings raised together express an aversion to the very idea of having sex with one another. Incest is avoided in all cultures, and laws and custom forbid it. Other animals also avoid incest; the offspring of primates and monkeys disperse from their groups when reaching maturity. Sibling aversion to sex is called the Westermarck Effect, named for its discoverer, Finnish researcher Edward Westermarck in the late 19th century. In Taiwan, some parents adopt unrelated girls and raise them alongside the parents’ sons with the intention of marrying them together. If the girls are adopted before age 30 months, they usually grow up to resist the idea of marriage, displaying the Westermarck Effect. If forced to marry, their divorce and adultery rates are much higher than normal, and the marriages produce 40% fewer children.

The source of this effect—cues triggered during play, eating together, aggression, or some other event or stimulus—is as yet unknown, and the theory is not fully proven. Led by Freud, psychoanalysts denied the Westermarck Effect, lest it upend the foundations of Freudian theory, which include the Oedipus Complex whereby boys want to have sex with their mothers and battle their fathers. Other theorists dislike the Westermarck theory because it suggests that modes and customs aren’t freely generated but instead derive from innate emotions. Even if the Westermarck Effect is true, it nonetheless is reinforced by social taboos generated by societies, many of which recognized the dangers of inbreeding long before the advent of genetic research. The Westermarck Effect demonstrates how genetics and culture are woven together in a complex fabric.