🦕Intro to Paleoanthropology Unit 13 – Human Evolution and Behavior

Key Concepts and Terminology

• Hominins refer to modern humans and extinct human species that are more closely related to humans than chimpanzees
• Bipedalism is the ability to walk on two legs, a key adaptation in human evolution that freed the hands for tool use and carrying objects
• Encephalization is the increase in brain size relative to body size over the course of human evolution
  • Encephalization quotient (EQ) measures the difference between actual brain size and expected brain size for an animal of a given size
• Australopithecines were early hominins that lived in Africa between 4.2 and 1.4 million years ago (Australopithecus afarensis, Australopithecus africanus)
• Homo is the genus that includes modern humans (Homo sapiens) and extinct species such as Homo habilis, Homo erectus, and Homo neanderthalensis
• Paleolithic period, also known as the Old Stone Age, is the earliest period of human history characterized by the use of stone tools (2.6 million to 10,000 years ago)
• Mitochondrial Eve is the most recent common matrilineal ancestor of all living humans, estimated to have lived around 150,000 years ago in Africa

Timeline of Human Evolution

• Sahelanthropus tchadensis is one of the oldest known hominins, living around 7 million years ago in Chad
• Australopithecus afarensis, including the famous "Lucy" fossil, lived in East Africa between 3.9 and 2.9 million years ago
• Homo habilis, the first species in the genus Homo, appeared around 2.3 million years ago in Africa and is associated with the earliest stone tools
• Homo erectus emerged in Africa around 1.9 million years ago and was the first hominin to migrate out of Africa, spreading across Asia and Europe
  • Homo erectus is known for the use of fire and more advanced stone tools (Acheulean handaxes)
• Homo sapiens, modern humans, originated in Africa around 300,000 years ago and began migrating to other continents around 70,000 years ago
• Homo neanderthalensis, Neanderthals, lived in Europe and parts of Asia from about 400,000 to 40,000 years ago, coexisting and interbreeding with Homo sapiens
• Homo floresiensis, nicknamed "hobbits" due to their small size, lived on the Indonesian island of Flores between 100,000 and 50,000 years ago

Major Hominid Species

• Ardipithecus ramidus lived in East Africa around 4.4 million years ago and shows early adaptations to bipedalism
• Australopithecus afarensis, an early hominin species, had a smaller brain size than later hominins but showed clear evidence of bipedalism
• Paranthropus boisei, also known as "Nutcracker Man," had large, powerful jaws and molars adapted for a diet of tough, abrasive foods (nuts, seeds)
• Homo habilis, the first species in the genus Homo, had a larger brain size than australopithecines and is associated with the earliest stone tools (Oldowan)
• Homo erectus was the first hominin to migrate out of Africa and had a larger brain size and more advanced stone tool technology compared to earlier species
  • Homo erectus is also known for the use of fire and the development of a more complex social structure
• Homo sapiens, modern humans, have the largest brain size relative to body size among hominins and are characterized by advanced cognitive abilities, language, and culture
• Homo neanderthalensis, Neanderthals, had a larger brain size than modern humans but went extinct around 40,000 years ago, possibly due to competition with Homo sapiens

Anatomical Changes and Adaptations

• Bipedalism evolved early in human evolution, as seen in Ardipithecus and Australopithecus, allowing for more efficient locomotion and freeing the hands for tool use
• Encephalization, the increase in brain size relative to body size, occurred throughout human evolution, with Homo sapiens having the largest relative brain size
  • Larger brains are associated with increased cognitive abilities, language, and social complexity
• Reduction in tooth and jaw size occurred as hominins shifted from a primarily plant-based diet to one that included more meat and cooked food
• Changes in the shape of the pelvis and spine accommodated bipedal locomotion and the need to balance the upper body over the lower limbs
• Development of the arch in the foot and the repositioning of the big toe in line with the other toes facilitated efficient bipedal walking and running
• Increase in manual dexterity and the ability to create and use tools with precision grip, particularly in Homo species
• Adaptations to varying climates, such as the development of sweat glands for efficient cooling and changes in body proportions (Bergmann's and Allen's rules)

Behavioral Developments

• Tool use and manufacture, beginning with simple Oldowan stone tools around 2.6 million years ago and progressing to more advanced Acheulean handaxes and other tools
  • Tool use allowed for access to new food sources (scavenging, hunting) and the processing of food (cutting, pounding)
• Use of fire, first evidence found in Homo erectus sites, provided benefits such as cooking, warmth, protection from predators, and extending activity into the night
• Language development, while difficult to trace in the fossil record, is thought to have emerged gradually, with Homo sapiens having full linguistic capabilities
  • Language facilitates complex social interactions, cooperation, and the transmission of knowledge and culture
• Expansion of diet to include more meat, either through scavenging or hunting, provided a high-energy food source that may have supported brain growth and development
• Emergence of symbolic thought and behavior, such as the creation of art (cave paintings, figurines), use of pigments, and burial of the dead
• Development of complex social structures and cooperation, as evidenced by the division of labor, group hunting, and care for the injured or elderly
• Spread of hominins across various environments and continents, adapting to new challenges and opportunities through behavioral and technological innovations

Tools and Technology

• Oldowan tools, the earliest known stone tools, were simple flakes and choppers used for cutting and pounding, associated with Homo habilis and early Homo erectus
• Acheulean tools, such as handaxes and cleavers, were more symmetrical and refined than Oldowan tools and were used by Homo erectus and later species
  • Acheulean tools were used for a variety of tasks, including butchering, woodworking, and digging for tubers and roots
• Levallois technique, a more advanced method of stone tool production, involved the preparation of a core to create flakes of predetermined shape and size
• Bone and antler tools, such as needles, awls, and harpoons, were used for tasks like sewing, leatherworking, and fishing
• Use of pigments, such as ochre, for symbolic or decorative purposes, as well as potential functional uses (hide tanning, insect repellent)
• Development of projectile technology, such as spears and bows and arrows, improved hunting efficiency and allowed for the exploitation of new food sources
• Creation of jewelry and other personal adornments, like beads and pendants, as expressions of identity, status, or group affiliation

Environmental Influences

• Climate change, such as glacial and interglacial periods, affected the distribution of resources and the survival strategies of hominins
  • Adaptations to colder climates included changes in body proportions (Neanderthals) and the use of fire and shelter
• Variability in habitat types (forests, grasslands, savannas) influenced the evolution of locomotion, diet, and social behavior in hominins
• Availability of food resources, such as plants, animals, and water, shaped hominin diets and foraging strategies
  • Shifts in diet, such as the increased consumption of meat, may have been driven by environmental changes that affected the abundance of plant foods
• Competition with other species, including other hominins and large predators, influenced the development of social behavior, technology, and cognitive abilities
• Dispersal and migration of hominins across continents were often driven by environmental factors, such as climate change or the pursuit of new resources
• Environmental pressures, such as droughts or volcanic eruptions, may have acted as selection factors, favoring individuals with certain adaptations or behaviors
• Interaction with the environment through the use of fire, tool use, and hunting likely had reciprocal effects on the ecosystem and hominin evolution

Current Research and Debates

• The role of climate change in shaping human evolution, particularly in relation to the development of bipedalism, brain size, and technology
• The importance of meat consumption in human evolution and its potential impact on brain growth and social behavior
  • Debates center around the relative contributions of hunting versus scavenging and the timing of increased meat consumption
• The origin and evolution of language, including the anatomical and cognitive prerequisites for language development and the potential role of gene-culture coevolution
• The relationship between Homo sapiens and other hominin species, such as Neanderthals and Denisovans, including the extent and consequences of interbreeding
  • Recent genetic evidence suggests that interbreeding between Homo sapiens and other hominins may have been more common than previously thought
• The role of social learning and cultural transmission in the development of technology, language, and other adaptive behaviors
• The "grandmother hypothesis," which proposes that the extended post-reproductive lifespan in humans evolved due to the benefits of grandmothers helping to care for and provision their grandchildren
• The timing and routes of hominin dispersals out of Africa and the factors that facilitated or hindered these migrations, such as climate, technology, and social structure
• The potential influence of epigenetic factors, such as DNA methylation and histone modification, on human evolution and the expression of adaptive traits