Evolution: The environmental context for hominin evolution in Southeast Asia

The evolution of hominins after their migration into Southeast Asia occurred against a backdrop of climate change in which the savannahs of the Middle Pleistocene eventually gave way to dense rainforest by the Holocene, according to a paper published this week in Nature. This analysis establishes the environmental context of hominin evolution in the region, and its association with animal extinction.

Southeast Asia is an important region for understanding hominin and mammalian migrations and extinctions. High-profile discoveries have shown that Southeast Asia has been home to at least five members of the genus Homo. Stable isotope tests, in which distinct carbon and oxygen isotopes can give clues about past plant life and water availability, have long been used to establish the environmental context of such evolutionary changes in Africa. However, few tests have been conducted in Southeast Asia.

Julien Louys and Patrick Roberts present a large-scale dataset of stable isotope data for Southeast Asian mammals that spans the Quaternary period (2.6 million years ago to the present). Their results show that the forests of the Early Pleistocene (around 2.6 million to 774 thousand years ago) had turned into savannahs by the Middle Pleistocene (after around 774 thousand years ago), which led to the spread of grazers and extinction of browsers (herbivores such as goats or deer, which eat leaves and fruits from shrubs). Savannahs retreated during the Late Pleistocene (from around 129 thousand years ago) and completely disappeared by the Holocene epoch (at 11.7 thousand years ago), replaced by closed-canopy rainforest. This change led to the domination of rainforest-adapted species—as well as the highly adaptable Homo sapiens—at the expense of savannah and woodland specialists, such as Homo erectus.