It is fascinating to see that the sense perceptions on which humans rely—taste, vision, hearing, smell, and others—arose with early animals and are shared to a large degree by all animals. These incoming sense perceptions, along with outgoing signals of sound and motion, provided information that linked individual animals into groups.
In this essay, I will outline the rise of—and cite key examples of—group behavior, which can be traced throughout the Animal Kingdom from early times to the present.
Tiny Animals and Their Senses
Life on Earth began more than 3 billion years ago with single-celled organisms, somewhat like bacteria. It was much later, some 570 million years ago, that more complex organisms known as animals arose. Early animals were tiny, multicellular, microbe-eating organisms with sexual reproduction. They settled in many local environments and gave birth to offspring that became the ancestors of the whole Animal Kingdom in the waters, on land, and in the air. These animals have continually changed over time—as individuals, as groups, and as whole species.
Animals required nourishment. They nourished themselves with food, water, and oxygen through intake organs such as the mouth, where the sense of taste developed to select the best food. Animal bodies transformed these life resources within digestive organs, then expelled the material waste in solid, liquid, and gaseous forms. Further, bodily organs produced information about the life resources consumed, sending it via neurons to be coordinated in the tiny brain.
Animals also needed to process information from external sources. They had to survive the impact of numerous environmental forces and impulses: The organisms, at their boundaries, encountered information on the physical forces and biological species of the environment, then developed organs that were able to sense these factors. For instance, the animal sense of touch responded to the impact and pressure of waves, wind, and vibrations of material bodies. And the force of gravity gave rise to the sense of balance, while a sense of temperature also developed.
Intake organs identified further details of the environment with senses of sight (from light waves sensed by eyes), sound (from audio waves sensed by ears), and smell (from chemicals). In addition to developing these sense perceptions, animals developed neurons and brains for transmitting electric signals that linked the organs to each other and used their combination to move the body and its parts.
Animals not only received sensory information, but they also emitted signals of information into the environment and to other animals. Audio signals were emitted by friction of various body parts that created audio waves; chemical signals or pheromones were emitted by the release of chemicals stored in the body; and visual signals arose indirectly because of body motion. (Ambient light—surrounding an organism—gave reflections of animal movement in the form of light waves. Such reflected light could then enable other animals to get a picture of a moving animal.)
Together, the reception of sensory perception and the emission of signals of information brought dynamic interaction of different types of information. This resulted in the creation of groups and group behavior in animals. Information about these groups was then shared in neural networks within animals and in environmental propagation of information between animals. It has been observed repeatedly that animal groups serve three basic functions: to create pairings for sexual reproduction, to facilitate foraging for food and shelter, and to protect against predators.
The underlying process of natural selection in biological organisms led to changes in the animals, their sensations, and their group behavior. Generation after generation, organisms developed organs that could sense information related to pressure or temperature or sound and translate that information into code for the neurons. These codes were gradually incorporated into the genomic data of the organism and could be inherited. Natural selection took the forms of genetic change, epigenetic change, and creation of new ecological niches. Natural selection also permitted the expansion of neuron bundles to reach all the bodily organs and the brains.
In sum, tiny animals, from the early days of their history, relied on sophisticated information about their environment and their neighbors. Varying species maintained the parallels in their life resources, senses, signals, and group behavior. Yet species diversified greatly, and their senses came to vary, too, aligning with the specificity of each animal’s ecological niche. Every animal required information on its environment (collected through the senses), information on the physical environment, and information on other organisms.
Later and Larger Animals and their Groups
In the warmth of the Cambrian Epoch, 541–485 ma, animals evolved rapidly, becoming larger and forming many different classes of species. They included the arthropods—the insects, crustaceans, and arachnids or spiders—with their exoskeletons and segmented units. Also numerous were the vertebrates—the fish, amphibians, reptiles, birds, and mammals—with their internal skeletons. Among the other life forms were cephalopods—octopi and squid—sea creatures with no skeletons.
Senses and signals were preserved in each class of animals, but in different ways. For instance, types of group activity distinguished the organism-based dynamics of animal groups from such environment-based dynamics as responses to temperature, light, and vibrations. The examples in this section show the variety of groups and the reliance of those groups on their basic senses and signals.
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- African fruit flies exhibit different types of group behavior. These flying insects have been used widely in biological experiments over the past century. Fruit flies have a full set of senses, including big eyes and taste receptors located in bristles on their legs, near the fruit they eat. Through video recordings, researchers Rebecca Rooke, Joel D. Levine, and colleagues, in Research Communities, summarized their recognition of the group behavior of flies. The flies maintain a minimal distance from each other to facilitate their foraging and to protect the deposit of their eggs. But linkages of each pair within fruit-fly groups vary with the size of the group; the interaction of each pair takes 1.5 seconds. Researchers applied Social Network Analysis (developed in study of human groups) within a social space, treating each networked group as an entity.
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- Schools of fish, especially Atlantic herring, synchronize their swimming in close formation so they all move at the same speed and in the same direction. To adjust their course, they rely on vision and their “lateral line,” an organ from gills to tail that is sensitive to changes in water currents, pressure, and vibration. When schooling fish stop to feed, rest, or spawn, they break ranks and become shoals (loosely connected groups of fish), but they can reform rapidly as schools. Schools of Atlantic herring have millions of members; many other fish have schools, though rarely as large.
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- Arctic terns, birds that migrate from the Arctic to Antarctic and back each year, developed a sense of magnetic patterns. Their beaks include fragments of magnetite (Fe2O3), iron-based crystals that yield information on the direction and intensity of the Earth’s magnetic field, enabling them to navigate their way north or south. This sense is called magnetoreception. In addition to Artic terns and European robins, magnetoreception may occur among other vertebrates, arthropods, and mollusks.
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- Beavers, among the largest of rodents, rely mostly on organism-based dynamics within their groups. But environment is central in selecting sites for dams, which provide living spaces for other plants, and animals. For example, Eurasian and North American species of beavers, which are fairly similar, occupy mostly wooded areas; have powerful incisors are for felling trees; and are able to chew and digest wood and to hold their breath for several minutes. These groups average about two adults and four offspring, with mates and offspring living together. They build dams to create ponds in streams and build lodges as homes in the pond (with underwater entrances). Each pond is its own an ecological community and halts erosion.
- Primates are an order of mammals including monkeys, apes, lemurs, and orangutans. Primates arose in tropical regions, living mostly in trees and feeding on fruit. They commonly have groups of about 40 members to protect against predators. Subgroups are for foraging and nurturing infants. Grooming, through touch, serves to maintain ties within families and friends. And as a result, primate brains have grown to facilitate intensive group relations.
These examples show how different species of the Animal Kingdom collect information on their world and develop shared senses. The information they take in—linked with the signals they outwardly project—has enabled the formation of groups that act according to the specific needs of each species. Animal species have thus thrived and expanded in many different directions.
Such group behavior extends even to the human province of the Animal Kingdom. In a later essay, I will argue that the human subgroup of primates also developed senses, signals, and groups. This behavior brought immense ecological change, enabling humans to spread everywhere on Earth.