Human evolution was very likely affected strongly by the dramatic climate swings of the Pleistocene.
These changes no doubt presented powerful new natural selection pressures. Many animal species were driven
to extinction by the advancing and retreating ice ages. Humanity survived primarily by becoming more
intelligent and adaptable.
This allowed us to develop new cultural technology to deal with cold environments and changing food sources,
especially during the last 1/4 million years. One of the greatest problems in the cold regions would have been the
relative scarcity of plant foods that humans could eat during the winters. In response to this, our ancestors became
more proficient at hunting animals, especially large ones that provided more calories.
This required inventing more sophisticated hunting skills as well as better weapons and butchering tools.
These changes in
subsistence pattern were essential for our survival.