image copyrightBBC News
Warning: Some readers may find the details of this story disturbing.
A descendant of our remote ancestors, barely 3 years old and with his baby teeth still coming in, wandered 2.8 million years ago through the swaying grass of the South African savanna.
The small Australopithecus africanus was unaware that someone was watching it from above.
Without warning, a huge bird of prey swooped down, caught the baby and killed it.
It is not known with certainty what type of bird devoured this infant - known as the "child of Taung" - but the perforation marks found under its eye sockets coincide with those left by the talons of an eagle; These birds usually hunt their prey in this way, and then store part of the catch in a tree or take the rest to their nest.
The Stone Age was a dangerous time to live in. Megafauna dominated the world.
The first humans coexisted with mammoths, mastodons, giant sloths, saber-toothed cats and enormous birds that devoured children.
For tens of millions of years, between the disappearance of the non-avian dinosaurs and the Great Ice Age, the skies were dominated by these giants.
End of Most read
His reign may have influenced the course of human evolution in profound ways that have often gone unnoticed.
It is believed that some of these creatures left their mark in legends about birds that abducted children, stories that have endured in various cultures around the world, long after these birds became extinct.
The origin of giant birds
All the news you need is on BBC World Service
Download it here
End of Ad app
When non-avian dinosaurs disappeared from the planet, the sky became covered in dust and most plants became extinct.
For the animals, there was hardly anything left to eat but seeds; something that, however, was very good for the birds.
In the absence of predators, some small, terrestrial birds with beaks managed to evolve into giants.
Some were herbivorous, such as Australia's dromornithids - known as "demon ducks of destiny" - which resembled modern ducks, but were 100 times larger and heavier than a cow.
Others took to the skies and transformed into enormous oceanic predators; Such is the case of Pelagornis sandersi -found in South Carolina-, the largest known flying bird, with an impressive wingspan of 7 meters.
There were also those that occupied the ecological niches that had been left empty after the extinction of large terrestrial predators, such as tyrannosaurs.
When large prey are available, even larger predators evolve.
These were the monstrous birds that our ancestors had to face.
image copyrightGetty Images
"As long as there have been primates, there have been birds of prey," says Scott McGraw, a primatologist at Ohio State University, US. "And birds of prey have always hunted primates, including us and our relatives."
Today, echoes of that ancient conflict between our ancestors and giant birds can still be seen in nature.
When McGraw examined the remains of more than 600 extant primates that had been killed by birds of prey - including the African crowned eagle - in the Taï forest of Ivory Coast, he discovered a striking similarity to the claw marks found on the remains of the "Taung boy."
In several skulls, the primates showed damage to the floor of the orbit, a bony surface inside the eye socket.
"That is, the eagle had removed the eyes, either by pecking them out or by tearing them out with a claw," McGraw explains.
"One of our researchers went to the fossil deposit, examined the 'Taung child' and found that the damage was identical."
Changes in our evolution
McGraw argues that birds of prey would have routinely devoured our human ancestors, and that predation by these birds may have been one of the most important selective forces in the evolution of primates, the order to which humans belong.
"If we go back and look more closely at the [human] fossil assemblages that have been collected over the years, it is very likely that, now that we know what to look for, we will find more evidence of damage caused by birds of prey. If what we observed at Taï is anything to go by, then this is commonplace."
There is little doubt in the paleoanthropological record that early humans were prey, says James Cole, an archaeologist and dean of applied sciences at the University of Brighton in the United Kingdom.
"Especially the oldest hominins, like that young specimen of Australopithecus africanus that was eaten by an eagle."
Cole points out that our ancient ancestors provided food for many predatory species. "We were certainly subject to predation."
image copyrightLos Angeles County Museum of Natural History
The need to avoid predators - from birds to leopards, hyenas and giant crocodiles - must have been a major evolutionary pressure for our ancestors.
It is believed that feeding giant birds influenced the configuration of both our body and mind.
Our ability to stand on two legs, for example, would have made it easier to detect predators.
Cooperation and altruism, interdependence and mutual protection could also have helped us.
Group size became of great importance, Cole notes: "There is strength in numbers" (or, literally, "there is safety in numbers").
When it comes to avoiding predatory birds, the larger the social group the better, McGraw adds.
Unlike predators that hunt their prey through active pursuit - such as lions or wolves - birds of prey are usually ambush predators.
They are stealthy and, in the case of crowned eagles, remain hidden in the trees until the right time comes.
This suggests that the human tendency towards social life may have been driven, in particular, by the need to avoid predatory birds; In this way, several people can remain alert in the event of a surprise attack, a phenomenon known as the "many eyes effect."
The emergence of language
Cole adds that the increase in group size could also have contributed to the emergence of the language.
"[In a large group], individuals begin to specialize in different functions. When some people perform one task while others do another, coordination is required. And once [a group] begins to fragment in this way, coordination can no longer depend solely on eye contact."
For simple communication – such as using hand gestures – to be effective, individuals need to be able to see each other, Cole says; However, when it is necessary to coordinate beyond the visual field - for example, to warn of the approach of a predator - "that is where language really begins to play a fundamental role."
McGraw suggests that the pressure to avoid death coming from above could even have been the trigger for the evolution of language.
There is evidence that most primates use generic alarm signals for various types of predators; For example, they use the same call for both a lion and a leopard.
However, in the presence of birds of prey, they react with specific calls. According to McGraw, this type of communicative behavior could be interpreted as a precursor to human language.
The culprits: eagles and teratornithids
The most significant encounter between giant predatory birds and our human ancestors is believed to have taken place in the Americas.
The first inhabitants of America coincided with the teratornithids. They were enormous carnivorous birds capable of swallowing their prey whole.
These birds, similar to condors, soared through the skies with a wingspan of up to 6 meters and acted as both scavengers and predators.
They were so large that they could take flight simply by spreading their wings and taking advantage of an upward current of air, explains Joanne Cooper, senior curator of bird anatomical collections at the Natural History Museum in London.
Teratornithids dominated the skies for about 25 million years and became extinct about 10,000 years ago, long after the first humans arrived in the Americas.
According to Cooper, it is possible that teratornithids inspired the legends about the "Thunderbird."
In Native American mythology, this creature has a colossal wingspan and is believed to control thunder and lightning.
Aiolornis incredibilis - also known as the "incredible teratorn" - terrorized southern California and Nevada, and had a wingspan of up to 5.5 meters.
Further north, in Oregon, Teratornis woodburnensis had a wingspan of 4 meters. This monster of the heavens lived about 12,000 years ago. Their remains were found alongside those of mammoths, mastodons and ground sloths, as well as early humans.
On the other side of the world, in New Zealand, experts suggest that the Maori legend of Te Hokioi - a gigantic eagle that abducted children - could have been based on a real species: the enormous, extinct Haast's eagle.
Haast's eagle was "essentially a flying tiger," Cooper says. Its weight was approximately twice that of an adult harpy eagle, one of the largest living eagles in existence.
Haast's eagle hunted another giant bird, although with terrestrial habits: the moa, which reached 4 meters in height.
This gigantic bird would dive - taking advantage of its weight to gain considerable acceleration - and hit its prey on the back with its 10 centimeter long claws, knocking it to the ground.
"We saw huge claw marks on some moa pelvises," says Cooper, who adds that Haast's eagle would have been perfectly capable of attacking humans.
"The children would have been in obvious danger. It must have been something impressive and, at the same time, terrifying."
Perhaps that is why legends about birds that kidnap children have endured, both in Maori and North American cultures and in Greek mythology; In the case of Greek mythology, storks did not bring babies, but rather stole them.
"When these birds fly over a place, they cast a shadow; and on a cultural level, they cast a very long shadow around the world," Cooper says.
The end of the air threat
In total, giant predatory birds dominated the skies for about 50 million years. Then, 2.6 million years ago, the Earth fell into the great ice age of the Pleistocene epoch.
The Pleistocene was a period of drastic climatic oscillations, which are believed to have driven human evolution.
By contrast, by the end of the era, 11,700 years ago, giant mammals were virtually extinct and larger predatory birds had also disappeared.
Experts are not clear whether the blame for the disappearance of megafauna lies with climate change or with human hunters. However, the expansion of human beings and the modifications we introduced into the ecosystem went hand in hand with the loss of up to 95% of all megafauna.
"We were either trying to eat them, or we were competing with them," Cooper says. Perhaps, he suggests, this explains the tension between humans and birds of prey that persists to this day.
"We are fascinated by them, we venerate them, but we are not particularly excited to live with them."
As the Pleistocene epoch was left behind, the climate began to stabilize. The glaciers retreated and humans began to practice agriculture. It was the dawn of a new era: the era of human beings.
Discover more
Video
End of Video
