Anthropocene Origin Tales: How Predators on the Pleistocene Savannah Made Us

Posted: November 27, 2014 in Anthropocene Origin Tales
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sabre tooth tiger eating human head

Early humans may have evolved as prey animals rather than as predators, suggest the remains of our prehistoric primate ancestors that were devoured by hungry birds and carnivorous mammals.

The discovery of multiple de-fleshed, chomped and gnawed bones from the extinct primates, which lived 16 to 20 million years ago on Rusinga Island, Kenya, was announced today at the Society of Vertebrate Paleontology’s 70th Anniversary Meeting in Pittsburgh.

At least one of the devoured primates, an early ape called Proconsul, is thought to have been an ancestor to both modern humans and chimpanzees. It, and other primates on the island, were also apparently good eats for numerous predators.

The ubiquitous Laurasian and African Late Eocene to Early Miocene apex predator Hyaenodon (Hyaenodontidae).

The ubiquitous Laurasian and African Late Eocene to Early Miocene apex predator Hyaenodon (Hyaenodontidae).

“I have observed multiple tooth pits and probable beak marks on these fossil primates, which are direct evidence for creodonts and raptors consuming these primates,” researcher Kirsten Jenkins told Discovery News.

Creodonts were ancient carnivorous mammals that filled a niche similar to that of modern carnivores, but are unrelated to today’s meat eaters, she explained. The Rusinga Island creodonts that fed on our primate ancestors were likely wolf-sized.

“There is one site on Rusinga Island with multiple Proconsul individuals all together and these are covered in tooth pits,” added Jenkins, a University of Minnesota anthropologist. “This kind of site was likely a creodont den or location where prey could be easily acquired.”

Analysis of tooth pits, de-fleshing marks, bone breakage patterns, gnawing and other damage to the primate bones indicate that raptors were also hunting down these distant relatives of humans.

“Primatologists have observed large raptors taking monkeys from trees,” Jenkins said. “When a raptor approaches a group of monkeys, those monkeys will make alarm calls to warn their group and attempt to retreat to lower branches. The primates on Rusinga had monkey-like postcrania and likely had very similar locomotor behavior.”

The study presents the first evidence of raptor predation on fossil primates from Rusinga, which was part of the side of a large volcano 20 million years ago.

Multiple ash layers suggest that eruptions killed countless animals from time to time. But when the volcano was inactive, the site supported a wooded area.

Jenkins is not certain what selective pressures predators placed on these very early primate ancestors to humans, but she said they “can affect behavior, group structure, body size and ontogeny (the life cycle of a single organism).”

Robert Sussman, professor of physical anthropology at Washington University in St. Louis, has long argued that primates, including early humans, evolved not as hunters but as prey of many predators, including wild dogs and cats, hyenas, eagles and crocodiles.

“Despite popular theories posed in research papers and popular literature, early man was not an aggressive killer,” said Sussman, author of the book “Man the Hunted: Primates, Predators and Human Evolution.” “Our intelligence, cooperation and many other features we have as modern humans developed from our attempts to out-smart the predator.”

He added that the idea of man as hunter “developed from a basic Judeo-Christian ideology of man being inherently evil, aggressive and a natural killer.”

“In fact, when you really examine the fossil and living non-human primate evidence, that is just not the case,” he explained.

Jenkins and her colleagues continue to excavate at Rusinga and nearby Mfangano islands, hoping to find more fossils — especially those from birds — so that the scientists can identify the species that were hunting the prehistoric primates.

A newfound horned crocodile may have been the largest predator encountered by our ancestors in Africa, researchers now suggest.

Scientists have even found bones from members of the human lineage bearing tooth marks from this reptile, whose scientific name, Crocodylus anthropophagus, means “man-eating crocodile.”

Scientists found a partial skull and skeleton of the crocodile at Olduvai Gorge in the Serengeti Plains of Tanzania in 2007. Past research there famously unearthed numerous fossils of extinct human species and their stone tools, strengthening the argument that our lineage originated in Africa.

Fossil leg and foot bones of at least two hominids from Olduvai bear crocodilian tooth marks, and came from roughly the same time as the newfound horned carnivore and within roughly 300 feet (100 meters) from where the reptile’s skeleton was discovered.

“I can’t guarantee these crocodiles were killing people, but they were certainly biting them,” Brochu said. “Our ancestors would have had to be cautious close to the water, because the water’s edge at Olduvai Gorge would have been a very dangerous place.”

Crocodiles may have been common predators of hominids, the scientists noted. Larger crocodiles would be capable of consuming our ancestors completely, leaving no trace.

“It was probably as large as a modern Nile crocodile, one of the largest living crocodilians at between 18 to 20 feet,” Brochu said. “One thing to bear in mind was that while these crocodiles are not necessarily bigger than the ones today, hominids back then were smaller than we are today, so the crocodiles would have been relatively quite a bit larger.”

Nor was it just cats. Humans were eaten by giant hyenas, cave bears, cave lions, eagles, snakes, other primates, wolves, saber-toothed cats, false saber-toothed cats, and maybe even—bless their hearts—giant, predatory kangaroos. Amazingly, these are just the predators that consumed our ancestors during relatively recent history, the past 100,000 years or so. Go further back in time, and the diversity of things that ate our kin goes up (particularly given that our earlier, pre-hominin ancestors were progressively smaller).  Some predators, such as leopards, ate many of our ancestors. Others, like crocodiles, komodo dragons, or sharks, took their bites, but more opportunistically, savoring the occasional human or proto-human the way one might enjoy some special holiday treat…

Even today, where humans live alongside predators, both children and adults get eaten. Harry Greene, a herpetologist at Cornell University and one of a handful of my colleagues more likely to be eaten by a wild animal than to die of old age, and Thomas Headland, an anthropologist, recently conducted a study of Agta hunter-gatherers in the Philippines. Harry was excited to find that the Agta lived among a high density of pythons. The Agta tend to be not quite so excited; Greene and Headland found that one in four Agta men had been attacked by a reticulated python. Of the 120 men whose stories were considered for the study, six had been killed by a python. That’s a death-by-python rate of 1 in 20…

Many primate species have alarm calls that are specific for different predators. The first primate nouns were almost certainly those embedded in calls that meant, “Oh shit, big cat!” “Oh shit, giant eagle!” or “For the love of god, did you see the size of that snake?”  In this way, predators may have had a positive impact on who we are now, having given us the precursors of language, or at the very least, cussing…

Many traits that influenced our ability to spot predators or flee from them have been under strong natural selection for much of the past 40 million years of primate evolution and even before then. (We have been prey essentially since the beginning.) Researchers are just beginning to explore these possibilities. Lynne Isbell at the University of California-Davis has argued that the range of our color vision evolved in part because those of our ancestors who could see more colors were more likely to spot snakes. A study this year found that children spot snakes more quickly than they do flowers . They also spot snakes when using color vision more quickly than in gray scale. Our interactions with other species (be they snakes, or as some have argued, fruits) shaped our eyesight. Our screams, those preverbal (and universal) utterances, are alarm calls signaling, simultaneously, both a threat and the need for help.

“How can the human eye can see more shades of green than any other color? ‘Cause of predators. Used to be, monkeys we were, right? And in the woods, in the jungle, everything’s green. So in order to not get eaten by panthers and bears and the like, we had to be able to see them, you know, in the grass, and trees and such. Predators”

~ Fargo 1×4: Eating the blame

In a way, of course, they were. All those gut feelings, right or wrong, that had kept the breed alive in the Pleistocene savannah—and they were wrong, so much of the time. False negatives, false  positives, the moral algebra of fat men pushed in front of onrushing trolleys. The strident emotional belief that children made you happy, even when all the data pointed to misery. The high-amplitude fear of sharks and dark-skinned snipers who would never kill you; indifference to all the toxins and pesticides that could. The mind was so rotten with misrepresentation that in some cases it literally had to be damaged before it could make a truly rational decision—and should some brain-lesioned mother abandon her baby in a burning house in order to save two strangers from the same fire, the rest of the world would be more likely to call her a monster than laud the rationality of her lifeboat ethics. Hell, rationality itself—the exalted Human ability to reason—hadn’t evolved in the pursuit of truth but simply to win arguments, to gain control: to bend others, by means logical or sophistic, to your will.

Truth had never been a priority. If believing a lie kept the genes proliferating, the system would believe that lie with all its heart.

Fossil feelings. Better off without them, once you’d outgrown the savannah and decided that Truth mattered after all. But Humanity wasn’t defined by arms and legs and upright posture. Humanity had evolved at the synapse as well as at the opposable thumb—and those misleading gut feelings were the very groundwork on which the whole damn clade had been built. Capuchins felt empathy. Chimps had an innate sense of fair play. You could look into the eyes of any cat or dog and see a connection there, a legacy of common subroutines and shared emotions.

The Bicamerals had cut away all that kinship in the name of something their stunted progenitors called Truth, and replaced it with—something else. They might look human. Their cellular metabolism might lie dead on the Kleiber curve. But to merely call them a cognitive subspecies was denial to the point of delusion. The wiring in those skulls wasn’t even mammalian anymore. A look into those sparkling eyes would show you nothing but—

~ Echopraxia by Peter Watts

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