Group behavior extends throughout the Animal Kingdom, even to its human province. The human subgroup of primates, like others, developed senses, signals, and groups. Ultimately, group behavior enabled humans to spread almost everywhere on Earth. Here is a quick look at five periods of existence of hominin species, tracing group behavior through their overall phenotype, the details of individual senses and signals, and the types of links among individuals that led to group behavior.
Hominin—6 million to 2 million years ago
Ecological niche and phenotype. As bipedal and omnivorous species, hominin species established their own domain. The apes of East African forests experienced drying of their environment: Forest become savanna and fruit became scarce. The emerging hominin species developed a bipedal stance, living on the ground rather than in trees. Their nutrition shifted from fruits alone to an omnivorous consumption of fruits, leaves, tubers, and seeds. Their hands became more dexterous, enabling them to create wooden and stone tools.
Senses, signals, and neurons. Taste expanded in response to wider diet; the sense of balance changed to support bipedalism. In open savanna, vision became more acute at a distance. In the signals of hominin, the motion of bipedalism and hand dexterity changed the vision of postures and moves seen by other hominin. Neuron density grew within individuals, tying together their organs of senses, signals, and the brain, especially neurons for walking, other motion, and vision.
Groups and links. Early hominin lived with polygamous intimate groups and with groups for foraging and community defense. The sense of animal touch was the basis of links in grooming among group members. Other links among individuals included audio waves conveying sound and light waves for vision.
Homo—2 million to 900,000 years ago
Ecological niche and phenotype. After an era of using pebble tools to forage marrow from bones of animal remains, Homo relied on Acheulean “hand axe” tools for quickly butchering large animals, thus providing them with meat that further expanded brain size. Homo rapidly grew nearly as tall as humans today: brain size doubled to 800 cc and community size rose to 80 members. They could run distances and migrated to new regions. Sweat glands expanded and fur disappeared. Whites of the eyes (sclera) became visible, so that one could see the gaze of others from a distance.
Senses, signals, and neurons. Taste changed as meat became more important in the diet. Temperature sense ranged more widely as Homo migrated to hotter and colder climates. Voice and hearing become more important. Motion changed with the expansion in running, and more neurons formed to support motion, as well as voice and hearing.
Groups and links. Intimate groups were polygamous, with lead males dominating two or more females. The call for assembly—similar to other animal communications—gathered groups to butcher large carcasses with Acheulean tools, repel competing carnivores, and carry off the flesh. The call for assembly came to be inherited genetically. Later, links through voice and hearing led to invention of a few descriptive words, which had to be learned by individuals and were then used by local groups. Links through vision allowed for observing motion, which helped observers learn how to butcher.
Heidelbergensis—800,000 to 300,000 years ago
Ecological niche and phenotype. Heidelbergensis built shelters, created clothing, controlled fire, and hunted with hafted spears made from prepared stone cores. Collaboration expanded through several mechanisms, including protolanguage. Heidelbergensis arose in Africa and spread to much of Africa and to Eurasia. Among early Heidelbergensis, head and face changed somewhat, and the brain expanded to over 1200 cc. Later, Heidelbergensis made wooden spears, built shelters, used fire in cooking, and prepared cores in stone that led to the development of more precise implements. Changes in social interaction took place through as many as four mechanisms: kin selection (Hamilton), dual inheritance (Boyd & Richerson), development (Tomasello), and gossip (Dunbar). Individual-level teaching and learning led to the exchange of tools and other practices.
Senses, signals, and neurons. Taste may have expanded as cooking became more significant. Animal touch may have evolved into shaking hands in greeting. Temperature senses broadened with increased migration to warmer and cooler regions. Neuron density expanded to reinforce voice and audio sense, to greater precision in motion, and to storing learned words in the brain.
Groups and links. As links among individuals expanded, informal groups began to emerge. They assembled at fireside, in dance, and in toolmaking; they assembled for hunting and for migration. Protolanguage, utilized by individuals and small groups for teaching and learning, arose to expand communication but remained limited in three ways. Vocabulary was restricted to perhaps a hundred words; words could not be linked; and speakers of each protolanguage were in groups of 15 to 30. For protolanguage, audio links required multiple steps: person A selected and spoke known words; the message traveled by sound; and person B received, translated, and acted on the message. Visual links required parallel but more complex and indirect ties.
Sapiens—350,000 to 20,000 years
Ecological niche and phenotype. Syntactic language brought explicit exchange of messages and ideas among groups of up to 150, enabling collaborations that brought rapid technological and social innovations. Early Sapiens, before 300,000 years ago, adopted the changes of Heidelbergensis but changed its intimate group to the household form, led by pair-bonded male and female. Households enabled Sapiens populations to grow. Later, Sapiens created spoken language in one or more communities in East Africa, around 70,000 years ago, then spread in all directions. Within 30,000 years, speaking humans had spread throughout Africa and Eurasia.
Senses, signals, and neurons. Taste broadened its dimension as cooking expanded. Temperature range expanded with increased migration. Propagation of sound changed as humans developed many new noises. Neuron density deepened with the creation of archives in each individual’s cerebral cortex, which stored vocabulary, syntax, and norms of the language institution. Each archive then grew to thousands of entries resulting from the individual’s years of study.
Groups and links. In contrast to informal groups, a We-group is an institution with defined membership requiring capacity to speak. The change was from protolanguage groups of 15 to 30 speakers to syntactic language groups of up to 150. In We-groups, members agreed to act in the interest of the group and perform its tasks. I have modeled the process of creating the initial We-group of adolescents, the years of their developing syntactic language, and the result, which yielded a community of 150 speaking people after about 30 to 40 years. Speakers used the common vocabulary and syntax, exchanging ideas with each other under the norms of the language-community institution. That is, each archive was linked to other archives through speech and hearing. Other links among individuals included enabling a speaker of one language to migrate into a group that speaks a different language.
Expanded Social Scale—from 20,000 years ago
Ecological niche and phenotype. In this steadily expanding niche, human communication and collaboration deepened, creating larger-scale activities. After language communities of 150 speakers spread worldwide, new and much larger social groups formed progressively. Cold weather of the Ice Age—at its worst 20,000 years ago—may have initiated such growth in social groups, but that expansion in social scale has continued to the present day.
Senses, signals, and neurons. The individual senses, signals, and neurons from ancestral times somehow played a role in the expansion in human social scale. Neuron density in individual humans arguably grew to account for the growing links between distant persons and groups. For instance, many individuals had to learn multiple languages.
Groups and links. Individuals were long members of multiple groups—households and communities, for example. Then human communities formed groups that were many times larger: groups of three communities formed confederations of 450; groups of three confederations formed ethnic groups of 1500; and the next level was societies of 4,500. How were links sustained? For distant members in a society, links of information from the sense of hearing or from the signal of voice could not connect without additional coordination. Thus, changes in neurons within individuals—and in links between group members—arguably arose to facilitate larger groups.
Conclusion
This framework distinguishes species according to phenotype, individual, and group behavior. It relies on individual sensing of the environment and on signals sending out messages. It suggests how individuals process information and how groups form and act. It also shows how individual and group interactions with the environment, guided by natural selection, allowed for the evolution of remarkable group activities in different animals.
For humans, such activities included bipedalism, social groups at multiple scales, innovation in technology, development from simple calls into articulate speech, formation of contractual groups, and large-scale learning. At present, we can acknowledge the need to continue this story: A new level of cooperation is required to avoid great damage to humanity’s hard-earned, complex social and ecological system.