FACT SHEETS

We were what we ate — clues to the survival of our earliest ancestors in teeth fossils

29.04.20 by By Zoë Taylor

Analysis of ancient teeth has unlocked surprising new insights into the ability of early humans to adapt to new and extreme environments.

The breakthrough came from a study of fossil teeth found during archaeological excavations of caves and rock shelters on two islands in a region known as Wallacea. Analysis of these fossils back in the lab allowed scientists to identify the diets of people living there tens of thousands of years ago.

New insights into the way people adapted after arriving on islands east of Wallace’s Line are revealed in the study published in Nature Communications.

Looking out of Makpan cave, near the village of Halmin, on Alor island, Indonesia. Image credit: ANU
Human and animal fossils
were used in the research to investigate diet
The fossils were found
during excavations on the islands of Alor and Timor-Leste
Wallace's Line and the islands of Alor and Timor-Leste.

The Wallacea region takes its name from Wallace’s Line — a boundary that separates the ecozone of Asia to the west from  Australasia to the east. It was named after British naturalist Alfred Russel Wallace, who, during his adventures in the ‘Malay Archipelago’ in the late 1850’s, noted the substantial difference in the types of plants and animals found on either side of the line he subsequently drew.

The research could hold further clues as to why Homo sapiens survived while other hominids became extinct, according to the researchers from Max Planck Institute for the Science of Human History, Germany, and from The Australian National University.

 

Ocean view from Makpan cave, near the village of Halmin, on Alor island, Indonesia. Image credit: ANU

Tropical forest settings, like those in Wallacea, are often considered barriers to human expansion and are a far cry from the sweeping savannahs with an abundance of medium to large mammals that early hominins are believed to have relied on for food and subsistence.

“The islands beyond Wallace’s Line 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 [about 2.6 million to 12 thousand years ago], and would have ensured that hominins had to make water crossings to reach it,” explains co-author Professor Sue O’Connor from The Australian National University and a Chief Investigator at CABAH.

Tropical forest settings, like those in Wallacea, are often considered barriers to human expansion and are a far cry from the sweeping savannahs with an abundance of medium to large mammals that early hominins are believed to have relied on for food and subsistence.

“The islands beyond Wallace’s Line 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 [about 2.6 million to 12 thousand years ago], and would have ensured that hominins had to make water crossings to reach it,” explains co-author Professor Sue O’Connor from The Australian National University and a Chief Investigator at CABAH.

While there is evidence of permanent occupation on some of the larger islands in the region such as Timor for at least the past 40,000 years. Less was known about the way early humans adapted to smaller islands like Alor, with theories that they may have been used as seasonal or temporary settlements. 

Working alongside villagers and with students and representatives from local universities, the team searched for suitable sites to investigate. In particular, the team targeted those locations most likely to contain evidence of people visiting them in the past — such as rock shelters and caves.

The identified sites — two on Alor and three on Timor Leste — were excavated in search of more clues to how early humans lived. Unsurprisingly, there was a mass of evidence uncovered that pointed to the extensive use of marine resources.

At one site called Makpan Cave (which translates to ‘echo’ in the local language due to its large size) a dig, covering two-metres square, included a shell midden and a burial site in its three metres depth. While an excavation at Tron Bon Lei rock shelter recovered almost 30,000 fishbones, at a site which also contained rock art, including depictions of boats.

Excavation at the Laili site on Timor-Leste. Image credit: ANU
Excavating Makpan cave, near the village of Halmin, on Alor island, Indonesia.

 

“Literally tonnes of marine resources are preserved in these archeological records,” explains co-author CABAH’s Dr Shimona Kealy of The Australian National University.

Using a technique called isotope analysis, the researchers analysed teeth from 26 different individuals to reconstruct their diet. The new research — based on this analysis of the tiny particles of tooth enamel — tells a fascinating story of the ingenuity and adaptability of early Homo sapiens.

“Stable carbon isotope analysis of hominin fossil tooth enamel has been used for a long time in Africa to study the diets and environments of some of our earliest ancestors,” says lead author Patrick Roberts from the Max Planck Institute in Germany.

“Different types of resources, such as those from dense tropical forests, grasslands, and the ocean, have different stable carbon isotope values. These differences are tracked into the tissues of animals that eat them.

“By studying the values of well-preserved human teeth, and comparing those to land and sea animals preserved at the same archaeological sites, we can get a better understanding of the overall reliance of an individual on these different food sources during the formation of their teeth.”

Read more in Dr Robert’s blog here.

 

Approximate proportions of marine, grassland and forest diets as revealed by isotope analysis of fossil teeth from Alor and Timor-Leste

 

Unsurprisingly, the results from a human fossil excavated from the site of Asitau Kuru on Timor-Leste suggest that the earliest people (we know of) were surviving mostly on a marine diet about 42,000 years ago.

“This fits with our existing models of rapid human movement through Wallacea on the way to Australia,” says Dr Kealy.

But from around 20,000 years ago, human diets seem to have switched inland, with the majority of the population no longer relying on a marine diet, but adapting to life in the tropical forests.

Dr Shimona Kealy (left) and Professor Sue O'Connor. Image credit: ANU
Walking to Makpan cave, near the village of Halmin, on Alor island, Indonesia. Image credit: ANU

“Because plants photosynthesise in different ways, we can use clear isotope signatures to distinguish between plants and animals from a forest, grassland or marine environment”, Dr Kealy explains.

“Our samples from before the last Ice Age show a reliance on marine resources at the stage of initial occupation. But what is surprising is that the isotope data show us that there was a quick transition to using a substantial amount of terrestrial resources.”

It is further evidence of the skills and adaptability of Homo sapiens.

Fossils and stone tool discoveries show that hominins — including the famous ‘Hobbit,’ or Homo floresiensis on the nearby island of Flores — made it to the Wallacean Islands at least a million years ago. When our own species arrived, more than 45,000 years ago, it is thought to have quickly developed the specialized use of marine habitats, as evidenced by one of the world’s earliest fish hooks found in the region.

As dense tropical rainforests replaced mixed grass and woodlands, other hominins in Southeast Asia went extinct. But ecological flexibility, supported by unique technologies and the capacity for social relationships and symbolism, seem to have carried Homo sapiens through the climatic fluctuations of the last Ice Age.

According to Dr Roberts, early human populations in Wallacea 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.” 

Dr Kealy adds: “We often don’t give these early explorers of our species enough credibility in their ingenuity.

“As far as we know, they were the only species to get to Sahul (the super-continent made up of PNG, Australia and Tasmania prior to sea level rise). Arrival in Australia may be the ultimate example of this ability to adapt in a short period of time. The resources for survival in Australia would have been completely different from anything that would have been encountered prior to getting here. And yet even our oldest archaeological sites show people were terrestrially focused.”

The researchers say more work needs to be done to try to tease out and test the distinctions between hominin species.

Nonetheless, for the time being it seems that it was our species that could best adapt to the variety of environments across the face of the planet, leaving it, by the end of the Pleistocene, the last man standing.

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