A new study of human teeth from islands in Southeast Asia shows how our earliest ancestors' diets set them up for survival in harsh, new environments, allowing them to thrive while other species died off.
The research team, including archaeologists from The Australian National University (ANU) studied a collection of human teeth found on the islands of Timor and Alor - part of the region known as Wallacea.
Co-author Professor Sue O'Connor said the study provides the first direct insights into the adaptations of our own species as it settled in a series of challenging island environments in Wallacea.
"We were able to see what these humans were eating while their teeth were being formed," Professor Sue O'Connor said.
"The earliest human fossils found in the region - dating to around 42,000 to 39,000 years ago - showed these people relied almost exclusively on resources from the sea to survive. This matches well with the food remains in the cave sites which comprised predominantly fish and shellfish in the earliest levels.
"But, from around 20,000 years ago, human diets seem to have switched, making use of the island forests resources. We don't know what caused the shift - but the resources inland were far more impoverished than what was available on the coastline. And yet our ancestors survived and thrived.
"Our findings align with other studies which show that our ancestors had this incredible ability to adapt to extreme environments.
"This supports the idea that a distinguishing characteristic of Homo sapiens is a high ecological flexibility, especially when compared to other hominins from the same region."
Professor O'Connor says the islands in the Wallacean region are ideal places to test the adaptive differences between our species and other hominins.
"These islands were never connected to mainland Southeast Asia during the Pleistocene period which lasted up to around 11,000 years ago. The hominins on these islands had to make water crossings to reach them, and once settled, had a limited range of resources. Our study shows humans not only settled there but managed to settle in for the long haul."
The researchers analysed tooth enamel from 26 different individuals to reconstruct their diet.
"These results give us another line of evidence to support the maritime capabilities of these earliest island explorers, while demonstrating their impressive capabilities for innovation and adaptation to new environments," said co-author Dr Shimona Kealy.
"All key factors in both their successful voyaging to Australia as well as their successful settlement on this unique continent."
According to lead author Patrick Roberts from the Max Planck Institute in Germany, early human populations in the Wallacea area and elsewhere "could not only use the enormous variety of often-extreme Pleistocene environments, they could also specialise in them over substantial periods of time."
"As a result, even if some local populations did fail, the species as a whole would go on to become tremendously prolific. It was this type of adaptive flexibility that saw our species go on to make the longer watercrossings required to colonise Australia".
The research has been published in Nature Communications.