Populations of Homo sapiens had spread across Africa by 330,000 years ago. Members of our species shared big brains that facilitated close interactions among networks of friends; they nurtured their offspring for years until puberty. Human networks ranged from households of about five members to communities of 150 members that protected the group. Households, mostly led by male-female pairs, provided food, sleep, repose, and nurtured offspring.
Biological evolution from early life
Biological evolution, through a process known as “natural selection,” brought gradual change to plants and animals. One evolutionary step was the appearance of Homo sapiens—its individuals, households, and communities—as early as 500,000 years ago. Darwin’s detailed theory of natural selection balanced three dimensions of change: variation of biological characteristics, reproduction of each characteristic from generation to generation, and selection in which some innovations survive and others do not.
- Variation: The phenotype means the observable characteristics of individual humans, groups, and the species. Variation in the phenotype takes place through mutation (usually random changes) of genetic constituents within human cells.
- Reproduction: The genome, as it replicates strands of DNA, also preserves each mutation. The sequence of reproduction runs from DNA to RNA to proteins and to the creation and modification of organs and practices, ultimately including characteristics of households and communities.
- Selection: The preservation of each genetic innovation as valuable to the organism takes place at the molecular level of the genome but also at other levels. For various reasons at the molecular level, the level of bodily organs, and because of environmental changes, some innovations become successful while others simply fail to be selected. The biological fitness of the revised organism is reflected in the rate of its reproduction of offspring in later generations.
Through these processes in African environments, networks of Homo sapiens strengthened households and communities, nurturing children who later took up community tasks. Further innovations from biological evolution included new tools, hunting, and mastery of fire. In a mental change known as Merge, two concepts could be combined and then linked to a third. The founding populations spread throughout Africa.
Cultural evolution from 300,000 years ago
Cultural evolution, a term developed in the 1980s, arose from the newly discovered biological processes of epigenetics and kin-selection. These processes permitted “social learning,” the preservation of knowledge exchanged among human brains. Such cultural evolution arose gradually but especially from about 300,000 years ago. The following analysis of variation, reproduction, and selection shows the parallels and differences of cultural evolution and biological evolution.
- Variation: The phenotype, for cultural evolution, includes observable characteristics arising not only from the genome but also from the characteristics of individual learning behavior and its influence on the community. Social learning posits individual learning through observations of each other or instruction by others—as in nurture of children or techniques for creating or using tools. At the genomic level, random mutations may yield changes that provide support for the newly learned activities, or they may undermine the new techniques.
- Reproduction: Newly learned activities are reproduced in individual brains and at genomic levels. Innovations in the brain are stored, retrieved, and passed on to others before the end of a generation. In the genome, phenotypical cooperation builds pressure for genetic mutations that reinforce the higher level of learning in individuals.
- Selection: At the brain level of the organism, selection of innovative practices requires consistent support by individuals, relearning the same lessons, and developing abilities to store and retrieve information. The process of dual inheritance requires that the individual-level and genome-level dynamics equilibrate with each other, so that collective behavior is gradually reinforced. The analysis also focuses on evolution of punishment to reaffirm cooperation.
The expansion of social learning brought higher levels of cooperation and competition. Households deepened child care and expanded household implements, jewelry, and decorative coloring with ochre. Communities drew on labor from households to create new tools of the Middle Stone Age, including stone tips linked to wooden spears and expanded the use of fire. Communication expanded with dancing, gestures, and networking—but not yet speech.
Social evolution from 70,000 years ago
Social evolution, the formation of conscious and goal-oriented groups, arose rather rapidly about 70,000 years ago. The two principal changes were in the rise of spoken language and in the organized group behavior of other social institutions. In each case, individuals agreed to form and maintain collaborative groups, making decisions within them that relied on huge amounts of individual learning.
- Variation: The phenotype, for social evolution, expands observable human characteristics to include collaborative social institutions. The innovative variation is that individuals consciously act to achieve a common task: this is the we-mode of collective intentionality. For language, this process required that individuals begin sharing words and sentences with agreed-upon syntax, using their internal Merge logic to construct understandable spoken sentences. Language was a social institution created among a group of about 15 juveniles as they played, combining learning skills, innovation, memorization, and communication.
- Reproduction: Institutional evolution takes place through reproduction of social institutions, beginning with syntactic language via reproduction of an archive of vocabulary and the norms of syntax. The archive of language was distributed among the brains of speakers: shared vocabulary and syntax were passed to the next generation by discussion at all levels. For other institutions, the patterns of leadership were passed on to members of the next generation.
- Selection: Social selection takes place at the community level rather than the individual organism level. Which social institutions, created by common effort, were to be propagated into the next generation? What practices were to be maintained within institutions? Institutional fitness was assessed in terms of social welfare—the institution’s benefits (over generations) to the capabilities of community members. Institutions that were seen as unsatisfactory to the community could be removed or at least revised substantially—especially at the time of generational change and the selection of new leadership.
New activities and goals of speaking communities included teaching language widely, marriages among households identified by name, creative representation in art and religion, and finely crafted Late Stone Age tools. Households took on the instruction of infants in speaking. Communities of 150, each with a language, migrated to settle the earth. With time, communities joined to create larger-scale societies, requiring still more labor from households.
With the rise of agriculture, households and communities divided up the productive tasks. In a resulting adjustment to expand the labor force, children came to be born with closer spacing. Societies developed new institutions for ceramics, metallurgy, religion, military, states, writing, and schools. Towns arose and some languages became widely spoken. Monasteries and military barracks replaced households for those who lived in them. Slavery changed households, as females headed slave households but free males owned the children. Most recently, working at home due to COVID-19 has transformed households. Still, households sustain themselves.
Human households and communities have evolved greatly, influenced by three regimes of evolutionary change. The changes have facilitated cooperation in humans but can also bring conflict. Biological evolution, through unconscious genetic change, adjusts human bodies and minds to their surroundings. Cultural evolution, through social learning in individual brains (with support from genetic and developmental change), builds new skills. Social evolution adds self-conscious, group-level decisions in language and institutions, to achieve chosen objectives. Communities became societies, which have expanded in laboring, invention, and change. Households adjusted to the changes, providing the comforts and labors of home and, especially, nurturing the children.