Lecture 23: Change in the Paleolithic Era
a series of ice ages. In the last million years, ice ages have normally lasted
about 100,000 years, with warmer “interglacials” of about 10,000 years in
between. Our species has already survived two ice ages. Today, we are at the
end of an interglacial that has already lasted 10,000 years.At the coldest phases, tundra-like steppes and deserts spread, forests retreated,
glaciers covered much of North America and northern Eurasia, sea levels fell
as water was locked up in glaciers, and plant growth was less vigorous in
middle and upper latitudes. These changes may have shaped the evolution
of our ancestors because, with their brains and their increasing ability to
network, they were ideally suited to survive such rapid environmental
changes. In summary, for most of the Paleolithic era, global climates were
generally colder and more arid than today, though these differences were less
marked in tropical regions than in higher latitudes.The most striking historical change in the Paleolithic era was the migration
of modern humans around the world. Humans were good at adapting to new
environments because, through collective learning, they kept generating new
technologies as they explored the environments at the edges of their home
ranges. Until about 100,000 years ago, all humans lived in Africa. During
this “African” era of human history, which includes at least half of human
history, humans settled new environments within Africa, adapting to deserts,
forests, and sea shores.In the last 100,000 years, some humans left Africa. Entering southern
Eurasia was not hard; indeed, other species (including ergaster) had made
similar migrations. But migrating further a¿ eld required more ingenuity.
At the height of the last ice age, when sea levels were lower than today,
Australia, Papua New Guinea, and Tasmania were joined in the single ice
age continent known as “Sahul.” Humans ¿ rst entered Sahul about 50,000
years ago, from what is today the archipelago of Indonesia. Reaching Sahul
required exceptional maritime skills, for migrants had to cross at least 40
miles of open water. When they arrived, they encountered completely
unknown environments, animals, and plants. No other species had made this
crossing successfully.