By Renaud Joannes-Boyau Ian Moffat Justin W. Adams and Luca Fiorenza / [19659002The
Australopithecus africanus, The distant ancestor of man had a unique approach to raising his cubs, as evidenced by our new research published today in Nature.
The geochemical analysis of four teeth shows that they exclusively breastfed infants for approximately 6-9 months before supplementing breastmilk with varying amounts of solid food until the age of 5-6 years. The balance between milk and solid foods varied cyclically during this period, probably in response to seasonal changes in food availability.
This knowledge is useful on several fronts. From an evolutionary perspective, it helps us to understand the particular biological and behavioral adaptations of Australopithecus africanus compared to other extinct human ancestors and modern humans. Breastfeeding over a period of up to 5-6 years, however, is metabolically expensive ̵
The use of milk as a dietary supplement for older offspring could have affected the survivability of the A. africanus species in a time of strongly changing climates.
Perhaps this lifestyle has accelerated the extinction of A. africanus about 2 million years ago.
An enigmatic hominin
A. africanus was first discovered in 1924 by Australian-born scientist Raymond Dart in Taung, South Africa, and represents the first early human ancestor identified from Africa. A century later, numerous early human ancestors were excavated and explored in Taung and other places in South Africa. This region is now a UNESCO World Heritage Site known as the "cradle of humanity".
This hominin species, a member of the human evolutionary lineage, exhibited a mixture of monkey-like and more specific traits. It was only recovered 3 to 2 million years ago from fossil sites in South Africa.
Illustration of a mother Australopithecus africanus and her young offspring. (Jose Garcia and Renaud Joannes-Boyau, Fair Use )
Since there are only a few specimens, there is little information on the life of A. africanus and its relationship to other fossil hominin species such as the Eastern African species of Australopithecus, the robust Paranthropus and our own genus Homo.
Zapping of teeth
Our research uses state-of-the-art analysis techniques. We used a laser to zap tiny pieces of fossil teeth and then used an instrument called a mass spectrometer to determine their chemical composition. This is much less destructive than conventional methods where the sample must be crushed and dissolved before analysis. 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 sample over the entire surface of a tooth – to determine changes in diet, mobility or climate over time. This is an important step forward as it can reveal information that could not be determined by traditional paleontological methods.
Schematic representation of the use of laser ablation analysis to illustrate the concentration of strontium and uranium in a tooth. (Renaud Joannes-Boyau, Fair Use )
In this study, changes in the concentration of barium, strontium, and lithium in fossil teeth were recorded by two individuals. The levels 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 assemble throughout our lives, our teeth do not change after they have formed in childhood. Teeth are therefore a perfect chemical time capsule of our childhood diet.
Illustration of a varied diet
The concentration of barium in breast milk is very high, so that even infant teeth that form during breastfeeding have a high concentration of this element. This concentration gradually decreases as other food sources are introduced.
The samples of A. africanus examined by us show a different pattern with cyclical fluctuations of the barium concentration. This suggests that mothers would increase or decrease the amount of additional feed, probably depending on the availability of other resources. This is an adaptation to the food stress that is also used by modern orangutans.
The lithium concentration in these teeth also varies cyclically, though not always concurrently with barium. The exact cause of lithium fluctuations is still unclear, but it seems that this is related to fluctuations in body fat reserves or protein intake. This suggests that A. africanus is regularly exposed to food stress and diet and / or fat reserves change with the seasons.
Australopithecus africanus teeth show a first period of silent behavior, followed by a cyclic signal in the lithium, strontium and barium distribution. (Renaud Joannes-Boyau, Fair Use )
We compared the results of A. africanus with modern animals from similar savanna-biome regions, demonstrating our results by showing a cyclic signal consistent with seasonal Variations related to signal interpreted as a cyclic breastfeeding even in modern orangutans.
We also examined the strontium isotopic composition of these teeth to understand where A. africanus moved through the landscape. Isotopes of the same element can be distinguished by their mass.
In paleontology, strontium isotopes are often used for this purpose because different regions have characteristic isotope values that are absorbed through food and drink. The two persons of A. africanus in our study seemed to have spent most of their lives near the Sterkfontein Cave, where their remains were found. Life in a region with limited food resources meant that these early hominins had eaten many different types of food that had been collected from different habitats to survive.
Strontium isotope ratio along the growth axis of an Australopithecus africanus tooth. (Renaud Joannes-Boyau, Fair Use )
Our research provides the first understanding of the still behavior of A. africanus. We now know that this breastfed hominin for a prolonged period of time, supplemented by varying amounts of solid food, which caused the fat reserves to fluctuate significantly. This was probably part of a largely successful survival strategy for the species.
However, as ecosystems changed with the climate about 2 million years ago, metabolic stress for mothers may have contributed to the potential extinction of this species.
Picture above: The teeth of these Australopithecus africanus skulls contain important information on the nutrition of these persons in adulthood. Source: Luca Fiorenza, Fair Use
Article # Tooth Time Capsule & # 39; reveals that 2 million years ago, early humans breastfed up to 6 years – by Renaud Joannes Boyau, Ian Moffat, Justin W. Adams and Luca Fiorenza were originally published on The Conversation and re-released under a Creative Commons license.