IV.

Biological Activity

The changing global temperatures and weather patterns of the Pleistocene Epoch affected animals and plants all over the world, even in areas untouched by ice. Some animals and plants moved from one continent to another, and some species became extinct.

Peat bogs that have preserved ancient plants and fossils of plants provide evidence of the characteristics of Pleistocene plant communities. Pollen grains, spores, seeds, leaves, twigs, and mosses all allow scientists to compare Pleistocene plants with modern ones.

The remains of simple animals provide additional information about climate and climatic change. Because different beetle species are especially well suited for either warm or cool climates, the presence of fossils of a particular type of beetle can provide scientists with clues to the climate of the region. Fossil algae reveal much about water acidity or alkalinity, water temperature, and the speed of water movement. The Ocean Drilling Program, which collects samples from the seafloor, has collected enough data to show that the distribution of marine organisms changed significantly during the Pleistocene Epoch.

Invertebrates—animals without backbones, such as shellfish and insects—and plant communities survived the glacial cycles of the Pleistocene relatively unscathed. Some animal and plant groups, such as the beetles, moved vast distances but underwent little or no evolution. Pleistocene mammals, on the other hand, underwent important changes, probably because climate changes affected mammals more than they did invertebrates. Many mammals have evolved significantly since the Pleistocene. Some changes in familiar animals include greater numbers of species of mice and rats and the appearance of modern species of the dog family.

Many mammalian species have become extinct since the Pleistocene. A few of the spectacular mammals that disappeared during the last 20,000 years include the woolly rhinoceros, the giant ground sloth, the saber-toothed tiger, the giant cave bear, the mastodon, and the woolly mammoth. These animals existed at the same time as early humans, and drawings of them exist on cave walls in Europe. Recent theories suggest that these huge mammals could not reproduce quickly enough to replace the number of animals that humans killed for food, and were therefore driven to extinction by human hunting.

Humans continued to evolve during the Pleistocene Epoch (see Human Evolution). Two genera, Australopithecus and Homo, existed during the early Pleistocene. The last australopithecines disappeared about one million years before present. Several species of the genus Homo existed during the Pleistocene. Modern humans (Homo sapiens) probably arose from Homo erectus, which are thought to have evolved from Homo habilis. Paleontologists have found fossils that support the transition between Homo erectus and Homo sapiens dating from about 500,000 years before present to about 200,000 years before present. Anatomically modern humans (Homo sapiens) arose from an earlier human species that lived in Africa. A likely ancestor, known as Homo ergaster, evolved by about 1.9 million years ago. This ancestor arose from an earlier Pleistocene species in Africa, perhaps one known as Homo rudolfensis. Anatomically modern Homo sapiens appear to have evolved by 130,000 years ago, if not earlier. For a time our species also coexisted in parts of Eurasia with another species of Homo, Homo neanderthalensis, until around 28,000 years ago (see Neandertals). Since then only our species has survived.