Early human species may have died out because mothers breastfed their kids too long

Did breastfeeding for too long contribute to the extinction of our distant ancestor Australopithecus africanus? A team of researchers has suggested that possible conclusion after a new examination of teeth.

At a certain point, mothers wean their children off breast milk so they can regularly eat solid foods. The World Health Organization recommends breastfeeding babies the first six months before weaning begins as breastfeeding tapers off over the next two years, perhaps earlier. Some mothers choose to breastfeed even longer that, which has been a source of controversy in our own society.

Female A. africanus skull. Image via Wikimedia
A. africanus child skull. Image via Wikimedia

But because breastfeeding requires resources to produce milk, it’s possible that doing it for too long can have an impact on resource availability. That’s what happened to a human species in South Africa known as Australopithecus africanus, according to a new study published in Nature.

The team of researchers sought to better understand the nutritional and dietary habits of these ancient ancestors, remains of whom are only found at a UNESCO World Heritage site known as “The Cradle of Humankind” where the Sterkfontein caves are located.

Sterkfontein caves in South Africa where A. africanus lived. Image via Wikimedia

They used special technology to analyze teeth from a skull dated to 2.6–2.1 million years ago.

“Our research takes advantage of cutting-edge analytical techniques,” the team wrote in an article about their results. “We used a laser to zap tiny pieces off fossil teeth, and then used an instrument called a mass spectrometer to determine their chemical composition.”

This is much less destructive than traditional methods that require the sample to 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 specimen across the entire surface of a tooth—illuminating changes in diet, mobility or climate through time. This is an important advance, as it can reveal information that has been impossible to establish using conventional palaeontological methods.

And what they found could be very helpful as modern humans deal with future resource shortages due to climate change.

“The balance between milk and solid food in this period varied cyclically, probably in response to seasonal changes in food availability,” the team wrote. “From an evolutionary point of view, it helps us understand the particular biological and behavioral adaptations of Australopithecus africanus compared to other extinct human ancestors and modern humans.”

The team discovered that Australopithecus africanus mothers continued breastfeeding their children until they were around five or six years of age, long after most modern humans stop doing so. And it was a costly decision.

“Breastfeeding for up to 5-6 years is metabolically expensive—it requires a certain input of calories for the lactating mother,” the team wrote. “Using milk as a supplemental food for older offspring may have hampered the ability of the A. africanus species to successfully survive during a period of substantially changing climate. Perhaps this way of life hastened the extinction of A. africanus around 2 million years ago.”

In order to reach this conclusion, the team had to look for specific elements in the teeth samples to find out the concentration of them, which would tell them how long breastfeeding occurred and how often.

While breastfeeding usually comes to a gradual halt once infants get used to eating other sources of food, Australopithecus africanus kept on breastfeeding for several years, and the team was even able to compare their results to modern-day orangutans.

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

The concentration of barium in breast milk is very high, so infant teeth that form during breastfeeding will also have a high concentration of this element. This concentration gradually drops as other sources of food are introduced.

The samples we analyzed from A. africanus show a different pattern, with cyclical fluctuations in barium concentration. This suggests mothers would increase or reduce the amount of additional food, probably depending on the availability of other resources. This is an adaptation to food stress also used by modern orangutans.

Analysis of lithium, strontium and barium levels in tooth samples. Image via Renaud Joannes-Boyau

While this strategy may have worked for the species in the past, it became a disadvantage as resources became more scarce.

Our research provides the first understanding of the nursing behavior of A. africanus. We now know this hominin had an extended period of breastfeeding supplemented by varying amounts of solid food that caused their fat reserves to fluctuate significantly.

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

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

Thus, breastfeeding for too long became a factor that resulted in the demise of the species.

Now, breastfeeding likely won’t be a cause of our own extinction. After all, we’re doing a pretty good job of that already by continuing to increase carbon emissions that are causing a disastrous rise in global temperatures. But there is a lesson to be learned here, and that’s that climate change is a significant threat to any species and has already wiped out many, including our own distant ancestors.

Breastfeeding for too long may have sped up their extinction, but climate change and lack of food resources are clearly the main factors that would have done the species in anyway even if breastfeeding had ceased at an earlier time.

Clearly, the more we learn about our ancestors, the more we learn about ourselves and how we can do things differently to make sure we survive as a species. Hopefully, we won’t suffer the same fate.

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Featured Image: Wikimedia

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