HOMININ MIGRATION - A RESPONSE TO CLIMATE CHANGE

Up to now, I have talked about numerous ways in which climatic variations affected human evolution, often deciding about a species’ survival or disappearance. However, I have not yet mentioned a very important consequence of climate change: migration. In today’s post I will explore all the complex migratory processes triggered by a changing climate.

Migration has been a typical behavioural reaction to changing climate since early days of hominin history – hominins (namely Homo erectus) first dispersed from Africa approximately 2 million years ago (Aguirre and Carbonell: 2001). Most commonly, hominin species followed flora and fauna they depended upon, and the extent of said flora and fauna shrunk and expanded with long- and short-term variations in climate. However, movements resulting just from habitat expansion did not need any major adaptation. Evolutionarily significant migrations happened when hominins dispersed to new habitats they had to adjust to.

So, let’s go back to arguably the most important migration in our history – H. erectus going out of Africa towards Asia ~2 Ma. That movement coincided with the increase in climatic variability and the gradual shift towards cooler and drier conditions in Africa I talked about quite a lot in my previous posts. Some scientists suggest that it was the changing climatic conditions that shaped the H. erectus morphology that allowed the migration, in particular longer lower limbs that permitted long distance locomotion, but also larger body size, linear body shape and nasal morphology (Eng: 1998). In other words, first the climate triggered the hominin adaptations to arid conditions, and then the adaptations proved to be useful for long-distance migration. And then, the first hominin dispersion led to the numerous speciation events of the hominin species in different regions of the world.    

Climatic variations could have added or removed some of the physical barriers, such as deserts or ice landmasses, for people moving because of resource depletion or population growth. For example, hominin expansion to the tropics occurred during cold, glacial intervals, when the sea levels were significantly lower (Hetherington and Reid: 2010). Also, interestingly, it is likely that genetic exchange between hominin populations increased during glacial intervals as people probably gathered in refugia and new paths opened due to a lower sea level (Antón: 2002, Keates: 2004). On the other hand, the migration towards higher latitudes took place during warm, interglacial intervals.

As usual, the migratory and evolutionary processes and their relation to climate change might be much more complex than we now understand. However, the story of hominin migration as a response to environmental change teaches us a very important lesson: hominin species thrived due to their intelligence, ability to move over large distances and adapt to new territories. Migration is, after all, more efficient and reasonable response to a changing climate than the gradual  process of natural selection and genetic change.