Hominins and Hominids
Throughout this report, the term hominin is used for any member of the evolutionary group of bipedal species most closely related to Homo sapiens that evolved following the split between humans and chimpanzees—it is a convenient way of referring to the evolutionary group that includes humans and our bipedal ancestors and evolutionary cousins. The term hominid includes all great apes, encompassing chimpanzees, gorillas, orangutans, and humans.
All living things interact with the earth system—the combination of land, atmosphere, and oceans—that make up our environment. As the earth system changes over time, individual species respond to these changes. In some cases, species disperse to new locations that match their preferred habitats. They may also adapt to the environmental changes, which sometimes leads to the formation of new species. And in some cases, species become extinct. A simple example in today’s world is the change in the range and population size of the polar bear. As Arctic climate has rapidly warmed over the past ~50 years it has become increasingly difficult for polar bears to feed, as their means of hunting—stalking seals from sea ice—has become more precarious as the Arctic ice pack retreats. Eventually, with a near total loss of summer ice cover in the Arctic Ocean, polar bears may become extinct. Through the processes of evolutionary change, dispersal, and extinction, organisms also modify the earth system, often in profound ways. On the largest scale, the evolution of oxygen-producing microorganisms permitted subsequent multicellular organisms to evolve. Or at a very local scale, large animals in Africa, such as elephants, substantially modify their physical environment by altering vegetation patterns and thereby affect the remainder of their ecological community. Study of the relationship between environment and evolution thus depends on understanding the basic interactions between biological and earth processes.
Humans are part of the global ecosystem and have an evolutionary history that has almost certainly been affected by—and in turn has affected—the earth system. The study of human evolution shows that, like other organisms, humans have evolved over a long period of time in the face of environmental challenges and opportunities. These challenges affected how early humans secured food, found shelter, escaped predators, and developed social interactions that favored survival. The capacity to make tools, share hunted-and-gathered food, control the use of fire, build shelters, and create complex societies based on symbolic communication set the stage for new ways in which humans interacted with their surroundings. More recently, humans have interacted with their surroundings