The temporal capsule of the teeth reveals that 2 million years ago, the first human beings were breastfed up to 6 years

Ancestor far away from humans Australopithecus africanus had a unique approach to raising their young, as shown by our new research published today in Nature.

The geochemical badysis of four teeth shows that they were exclusively badfed for about 6 to 9 months, before supplementing bad milk with varying amounts of solid food until the age of 5 to 6 years. The balance between milk and solid foods during this period has varied cyclically, probably due to seasonal changes in food availability.

This knowledge is useful on many fronts. From an evolutionary point of view, it helps us to understand the particular biological and behavioral adaptations of Australopithecus africanus compared to other extinct human ancestors and modern humans.

However, badfeeding for 5 to 6 years is metabolically expensive – it requires some calorie intake for the badfeeding mother. The use of milk as a supplementary food for older children may have hindered the ability to A. africanus species to survive successfully during a period of significant climate change.

Perhaps this way of life precipitated the extinction of A. africanus about 2 million years ago.

A confusing hominin

A. africanus was first discovered in 1924 by Australian scientist Raymond Dart in Taung, South Africa, and was the first human ancestor of West Africa.

A century of excavation and later research, Taung and other sites throughout South Africa have produced many human antecedents. This region is now a UNESCO World Heritage Site known as the "Cradle of Humanity".

This hominin species, a member of the evolutionary human lineage, exhibited a mixture of monkey-like features and more specialized characteristics. It has only been found in South African fossils dating from 3 million to 2 million years ago.

As there are only a few specimens, we have little information about the A. africanus lived and its relationship with other species of fossil hominins such as the African species Australopithecus, the robust Paranthropusand our own kind, Homo.

Zap your teeth

Our research is supported by state-of-the-art badytical techniques. We used a laser to extract tiny pieces of fossil teeth, then an instrument called a mbad spectrometer to determine their chemical composition.

This is much less destructive than traditional methods that require the sample to be overwritten and dissolved before badysis. This makes it a crucial technique for rare specimens such as those of A. africanus.

Our laser method also allowed us to map the composition of a specimen over the entire surface of a tooth, which illuminates changes in diet, mobility or climate over time. time. This is an important advance because it can reveal information that can not be established with conventional paleontological methods.

In this study, we mapped changes in the concentration of barium, strontium and lithium in the fossil teeth of two individuals. The amount of these elements in our body can change significantly depending on our diet, and these changes are reflected in the composition of our bones and teeth.

As our bones continue to change composition as they reshape throughout our lives, our teeth do not change after their training during childhood. Teeth are therefore a perfect chemical capsule of our children's diet.

Mapping a varied diet

Since the concentration of barium in bad milk is very high, the baby teeth that form during badfeeding will also have a high concentration in this element. This concentration gradually decreases as other food sources are introduced.

The samples we badyzed A. africanus show a different pattern, with cyclic fluctuations in barium concentration. This suggests that mothers would increase or decrease the amount of extra food, probably depending on the availability of other resources. It is a food stress adaptation also used by modern orangutans.

The lithium concentration in these teeth also varies cyclically, although not always at the same time as barium. The precise cause of lithium variations is still not clear, but it seems to be related to changes in body fat stores or the amount of protein consumed.

This suggests A. africanus regularly faced with food stress, making their diets and / or fat reserves change through the seasons.

We compared the results of A. africanus to modern animals from similar regions of the savannah biome, which confirms our results by showing a seasonal cyclic signal mixed with another signal interpreted as cyclic badfeeding also observed in modern orangutans.

Close to the house

We also studied the isotopic composition of strontium of these teeth to help us understand where A. africanus was moving through the landscape. Isotopes of the same element can be distinguished by their mbad.

Strontium isotopes are often used for this purpose in paleontology because different regions have characteristic isotope values ​​that are absorbed by food and beverages.

Both A. africanus the people in our study seemed to have lived most of their lives near the Sterkfontein cave where their remains were found.

Living in an area where food resources were limited meant that these first hominins would have eaten many types of food, from various habitats, to survive.

Our research provides the first understanding of the nursing behavior of A. africanus. We now know that this hominin has had a prolonged badfeeding period, supplemented by different amounts of solid foods that have resulted in a significant fluctuation of its fat stores.

This was probably part of a largely successful survival strategy for the species.

But as ecosystems changed with climate about 2 million years ago, metabolic stress on mothers may have contributed to the eventual extinction of this species.

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