You are an Australopithecus living in the African rainforests. Your life is pretty good, you basically climb from one tree to another collecting fruits, avoiding predators and looking for shelter. However, at the other side of the Atlantic Ocean, the Panama isthmus just closed, and it’s about to trigger a change in the oceanic circulation that eventually will convert your home in an arid desert. Yes, it’s time to say goodbye to your comfort zone!

isthmus
Before the Isthmus closed. Source: phys.org

Around 4 million years ago, the Isthmus of Panama formed, creating a continental mass that connected South America with North America, and therefore, closing the ocean channel that linked Pacific and Atlantic waters, which was traduced in more water vapor at higher latitudes that precipitated as snow in the winter.

 

At that time, the African climate was moist and warm, regulated mainly by low-latitude insolation and monsoons. Rainforests and woodlands were the habitat for a great diversity of species such as the Australopithecus – the human ancestor – as well as ferocious predators like lions, cheetahs, hyenas or the Dinofelis, an extinct sabre-tooth cat. In that context, is easy to imagine why our ancestors were so attached to trees, they were not only their source of food, but also their way to escape this dangerous animals.

austrolopithecus_dinofelis
Australopithecus and Dinofelis. Source: Smithsonian and “Earth System History” by S. Stanley

obliquitySeveral hundreds of thousands of years passed until the Earth rotation axis changed sufficiently to decrease the temperatures in the summer and prevented the high latitude snow from melting. Giving origin to ice sheets formation in the north and to a completely new era in which the Earth would be shifting for glacial to interglacial periods, starting 2.5 million years ago. This new global climate dramatically reduced the moisture of Africa and converted it into an arid region.

 

The Australopithecus experienced then an ecological crisis. The forests were replaced by grasslands and their source of food and shelter was gone, and only a few populations survived. However, with this vanishing of their tree dependence, some evolutionary changes were enabled.

The mothers were now able to hold their newborns in her arms for longer periods since they were not climbing trees all the time. Helpless infants with bigger brains were now able to survive, which couldn’t be possible if they needed to hold to a tree-climbing mother due to their unproportioned body and head size.

This populations eventually evolved into the early Homo, a species of higher cranial capacity that were able to create stone tools, which ultimately resulted much more benefic than climbing trees.

earlyhomo_cranialsize
Early Homo with bigger cranial size

In summary, a change in oceanic circulation generated high latitude snow precipitation that with the right conditions formed the ice sheets and resulted in a great step on the history of human evolution. This case study reflects the great implications that climate change could have on ecosystems and species, as well as the key roles of different components of the climate, such as insolation and ocean circulation.

So do you think current climate change will give place to a more evolved species than humans? Or we would rather destroy the world before that happens?