The period of human evolution has coincided with environmental change, including cooling, drying, and wider climate fluctuations over time. How did environmental change shape the evolution of new adaptations, the origin and extinction of early hominin species, and the emergence of our species, Homo sapiens? (‘Hominin’ refers to any bipedal species closely related to humans – that is, on the human divide of the evolutionary tree since human and chimpanzee ancestors branched off from a common ancestor sometime between 6 and 8 million years ago.)
How do we know Earth’s climate has changed? How quickly and how much has climate changed? One important line of evidence is the record of oxygen isotopes through time. This record of δ18O, or oxygen stable isotopes, comes from measuring oxygen in the microscopic skeletons of foraminifera (forams, for short) that lived on the sea floor. This measure can be used as an indicator of changing temperature and glacial ice over time. There are two main trends: an overall decrease in temperature and a larger degree of climate fluctuation over time. The amount of variability in environmental conditions was greater in the later stages of human evolution than in the earlier stages.
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Many Americans opposed the war on moral grounds, appalled by the devastation and violence of the war. Others claimed the conflict was a war against Vietnamese independence, or an intervention in a foreign civil war; others opposed it because they felt it lacked clear objectives and appeared to be unwinnable.
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