Climate effects on human evolution

• Bipedalism allowed hominids to walk more efficiently over long distances, facilitating migration to new habitats.
• Key human adaptations evolved in response to environmental instability
• Natural selection was not always about 'survival of the fittest' but also about survival of those most adaptable to changing surroundings
• Diverse species have emerged over human evolution, accumulating adaptations such as upright walking, tool-making, brain enlargement, prolonged maturation, complex mental and social behavior, and dependence on technology
• Human evolution coincided with environmental change, including cooling, drying, and wider climate fluctuations over time
• Record of oxygen isotopes in foraminifera skeletons indicates changing temperature and glacial ice over time
• Overall trend during human evolution has been towards a cooler, glaciated world
• Amplitude of oscillation increased around 6 million years ago and became larger over the past 2.5 million years
• Evolution of Homo genus and Homo sapiens adaptations associated with largest oscillations in global climate
• Organisms encounter environmental changes including shifts in temperature, precipitation, vegetation, tectonics, volcanic eruptions, and forest fires
• Effects of environmental changes lasted for many years, raising instability and uncertainty in survival conditions
• Ability to adjust to different habitats and environments is a characteristic of humans
• Three possible outcomes of population evolution in environmental dynamics: move and track habitat change, expand adaptive versatility, or face extinction
• Adaptations such as upright walking or tool-making may have been associated with drier habitats and the spread of grasslands
• Variability selection hypothesis suggests that key events in human evolution were shaped by environmental instability, not by a single type of habitat or environmental trend
• Hominins evolved the ability to respond to shifting surroundings and new environmental conditions by increasing their ability to cope with changing habitats rather than specializing in a single type of environment
• Organisms cope with environmental fluctuation through genetic adaptation and phenotypic plasticity, as well as evolving structures and behaviors to cope with different environments
• Variability selection hypothesis suggests that structures and behaviors enabling coping with changing and unpredictable conditions are favored in highly variable environments
• Human traits evolved over time to adjust to environmental uncertainty and change, improving the ability of early human ancestors to deal with habitat change and environmental diversity
• Hominins evolved during an environmentally variable time, with higher variability occurring as changes in seasonality produced large-scale environmental fluctuations over periods lasting tens of thousands of years
• Variability selection hypothesis addresses how adaptability can evolve over time
• Stone toolmaking allowed ancient hominins to access diverse foods
• Hominin toolmakers possessed sharp flakes for cutting and hammerstones for pounding and crushing foods
• Basic stone tools greatly enhanced the functions of teeth, allowing access to a variety of foods
• Stone tools were used to slice meat from large animals, break open bones to access marrow, grind plants, and sharpen sticks to dig for tubers
• Tool use widened the diet of hominins and made it easier to obtain food from different sources
• The first known stone tools date back to around 3.3 million years ago
• Stone toolmaking conferred versatility in how hominin toolmakers interacted with and adjusted to their surroundings
• Enlargement of the brain during human evolution allowed hominins to process and store information, plan ahead, and solve abstract problems
• Brain enlargement coincided with the period of strongest climate fluctuation worldwide
• After 400,000 years ago, hominins created a variety of different tools to cope with the environment
• Technological innovations in the Middle Stone Age in Africa provided new ways for hominins to access food
• New tools included points hafted for hunting, barbed points for fishing, grindstones for processing plant foods, and tools for making clothing
• Over the past 300,000 years, the direct ancestors of living humans developed the capacity to create new and diverse tools
• Wider social networks began to arise, enabling the transfer of stone material over long distances
• Trading between groups to obtain materials and to cement alliances became a hallmark of modern human behavior
• Evidence of the human capacity for communication using symbols dates back to at least 250,000 years ago
• Symbolic communication may be linked with information storage and language is an essential part of modern human communication
• Use of symbols is connected to the human ability to plan, record information, and imagine
• Humans today use resources from a vast variety of plants and animals, many specialized tools, and have social contacts and means of exchanging resources and information to survive in a changing world