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Mid-Pleistocene climate change may have shaped hominin development and dispersal

A multi-institutional team of evolutionary specialists, climatologists and sociologists has found evidence that climate change during and after the Mid-Pleistocene likely shaped hominin development in parts of what is now Asia.

The work, in the journal Nature Communications, began with the observation that following the Mid-Pleistocene, ice ages began lasting longer, leading to permanent climate changes that species, including hominins, had to deal with or perish.

Prior to what has come to be known as the Mid-Pleistocene Climate Transition (MPT), ice ages tended to last on average 40,000 years. After the MPT, they spanned up to 100,000 years. Such lengthy periods, the researchers note, meant that permanent changes occurred in many parts of Asia.

Places that had once been forest, for example, became grasslands, deserts or loess plains, depending on the degree to which rainfall was reduced during the ice ages. In this new study, the research team looked into adaptations hominins must have made to survive.

To better understand the environmental changes, the research team collected and analyzed loess deposits from several sites across Central Asia, and most specifically, northwest parts of China. Such deposits provide historical information, such as the types and levels of carbon isotopes. By noting their depth at a dig site, the researchers were able to use the samples to measure rainfall.

The samples showed dramatically lower levels of precipitation during some ice ages, which would have meant drastic changes to vegetation and the species that relied on them for food. The team also noted that as vegetation changed, so would the landscape as exposure to wind erosion increased. Changing rain patterns also likely meant more flooding, and sometimes, changes to major river systems.

Such changes would have required adjustments by early hominins, such as moving to more favorable places or changing their diet. The researchers also note that major changes to rivers like the Yellow River likely provided much more fresh water, making survival easier.