The Pleistocene Epoch began about 2.5 million years ago and ended about 11,700 years ago. During the Pleistocene, periods of glacial expansion alternated with glaciers receding during warmer periods. This was a time of giant Megafauna, the Ice Age, and the expansion of our genus, Homo. It is difficult for modern humans to comprehend what living beside these giant mammals might have been like for our ancestral species.
Imagine crawling down from the relative safety of your tree or walking out of your cave to see: giant armadillos that weighed over a ton, sloths that were 10’ tall and weighed 2,200 lbs., giant beavers the size of Volkswagons, camels with shoulders over 7’ tall, dire wolves, woolly mammoths, 14’ tall mastodons with shaggy coats and long, curved tusks, giant saber-toothed cats, birds of prey with 23’ wingspans, and short-faced bears who have been compared to grizzly bears on stilts that could run at high speeds and chase down prey.
Not only did our ancestors live among these giant mammals, but also among a changing environment described below in LiveScience.com:
“At the time of the Pleistocene, the continents had moved to their current positions. At one point during the Ice Age, sheets of ice covered all of Antarctica, large parts of Europe, North America, and South America, and small areas in Asia. In North America, they stretched over Greenland and Canada and parts of the northern United States. The remains of glaciers of the Ice Age can still be seen in parts of the world, including Greenland and Antarctica.
“But the glaciers did not just sit there. There was a lot of movement over time, and there were about 20 cycles when the glaciers would advance and retreat as they thawed and refroze…
“While scientists haven’t been able to determine the exact causes of an epoch, changes in ocean current, composition of the atmosphere, changes in the position of the Earth in relation to the sun are believed to be key contributors.
“Overall, the climate was much colder and drier than it is today. Since most of the water on Earth’s surface was ice, there was little precipitation and rainfall was about half of what it is today. During peak periods with most of the water frozen, global average temperatures were 5 to 10 degrees C (9 to 18 degrees F) below today’s temperature norms.
“There were winters and summers during that period. The variation in temperatures produced glacial advances, because the cooler summers didn’t completely melt the snow.” (Zimmerman, 2017)
So after our early ancestors adapted to the heat of the Pliocene epoch, shed most of their body hair and developed advanced sweat glands to cool their growing brains and bodies, the family of early Homo species transitioned into the Ice Age.
Among the more recent species is Homo heidelbergensis:
“An extinct species of archaic human (genus Homo) known from fossils dating from 600,000 to 200,000 years ago in Africa, Europe, and possibly Asia. The name first appeared in print in 1908 to accommodate an ancient human jaw discovered in 1907 near the town of Mauer, 16 km (10 miles) southeast of Heidelberg, Germany. Among the fossils found with the Heidelberg jaw were those of several extinct mammals that lived about 500,000 years ago.
“The Heidelberg jaw, also called the Mauer jaw, lacks a chin and is exceptionally thick and broad. The teeth are surprisingly small for such a massive mandible. The jaw is also long, and this feature may imply that the individual had a projecting lower face. Among other examples of H. heidelbergensis, the best are specimens from Bodo (Ethiopia), Kabwe (Zambia),
Ndutu (Tanzania), Petralona (Greece), Arago (France), and possibly Dali (China). The craniums have massive brow ridges, a long and low braincase, and thick vault bones like those of H. erectus. The braincases are larger than what is typical for H. erectus, but the skulls lack the unique specializations that characterize the Neanderthals. The expanded brain necessitates the modern features seen in the skull, such as the more-rounded rear of the skull (occipital), expanded sides (parietals), and broadened forehead…
“It appears to many researchers that H. heidelbergensis is the common ancestor of both Neanderthals and modern humans and that the transition from H. heidelbergensis to H. sapiens occurred in Africa prior to 300,000 years ago.” (McHenry, 2019) (to be continued in next post)