Human ancestors not to blame for ancient mammal extinctions in Africa

Early human ancestors not to blame for extinctions of giant African mammals
Africa contains the greatest diversity of large-bodied mammals in the world today. This includes five species of megaherbivores (herbivores over 2000 lbs). From left to right: hippopotamus (Hippopotamus amphibius), giraffe (Giraffa camelopardalis), elephant (Loxodonta africana), white rhino (Ceratotherium simum), and black rhino (Diceros bicornis). Credit: John Rowan

New research disputes a long-held view that our earliest tool-bearing ancestors contributed to the demise of large mammals in Africa over the last several million years. Instead, the researchers argue that long-term environmental change drove the extinctions, mainly in the form of grassland expansion likely caused by falling atmospheric carbon dioxide (CO2) levels.

Tyler Faith, curator of archaeology at the Natural History Museum of Utah and assistant professor in the Department of Anthropology at the University of Utah, led the study. The research team also includes John Rowan from the University of Massachusetts Amherst, Andrew Du from the University of Chicago, and Paul Koch from the University of California, Santa Cruz.

The study is published today in the journal Science.

"Despite decades of literature asserting that early hominins impacted ancient African faunas, there have been few attempts to actually test this scenario or to explore alternatives," Faith says. "We think our study is a major step towards understanding the depth of anthropogenic impacts on large mammal communities, and provides a convincing counter-argument to these long-held views about our early ancestors."

To test for ancient hominin impacts, the researchers compiled a seven-million-year record of herbivore extinctions in eastern Africa, focusing on the very largest , the so-called 'megaherbivores' (species over 2,000 lbs.) Though only five megaherbivores exist in Africa today, there was a much greater diversity in the past. For example, three-million-year-old 'Lucy' (Australopithecus afarensis) shared her woodland landscape with three giraffes, two rhinos, a hippo, and four elephant-like species at Hadar, Ethiopia.

Today, Africa has five species of massive, plant-eating mammals, the so-called megaherbivores: Elephants, hippos, giraffes, and white and black rhinos. Millions of years ago, however, there was a much greater diversity. When and why these species disappeared has long been a mystery for archaeologists and paleontologists, despite the evolution of tool-using and meat-eating hominins getting most of the blame.New research disputes a long-held view that our earliest tool-bearing ancestors contributed to the demise of large mammals in Africa over the last several million years. Instead, the researchers argue that long-term environmental change drove the extinctions, mainly in the form of grassland expansion likely caused by falling atmospheric carbon dioxide levels.Video based on:J. Tyler Faith, John Rowan, Andrew Du, Paul L. Koch. 2018. Plio-Pleistocene decline of African megaherbivores: No evidence for ancient hominin impacts. Science. Nov. 23, 2018.(DOI: 10.1126/science.aau2728) Credit: Lisa Potter

When and why these species disappeared has long been a mystery for archaeologists and paleontologists, despite the evolution of tool-using and meat-eating hominins getting most of the blame.

"Our analyses show that there is a steady, long-term decline of megaherbivore diversity beginning around 4.6 million years ago. This extinction process kicks in over a million years before the very earliest evidence for human ancestors making tools or butchering animal carcasses and well before the appearance of any hominin species realistically capable of hunting them, like Homo erectus," says Faith.

Human ancestors not to blame for ancient mammal extinctions in Africa
The team analyzed more than 100 sites in East Africa with rich fossil records to track the longterm decline of megaherbivore diversity. Credit: J. Tyler Faith
Taking a Closer Look

Faith and his team quantified long-term changes in eastern African megaherbivores using a dataset of more than 100 fossil assemblages spanning the last seven million years. The team also examined independent records of climatic and environmental trends and their effects, specifically global atmospheric CO2, stable carbon isotope records of vegetation structure, and stable carbon isotopes of eastern African fossil herbivore teeth, among others.

Their analysis reveals that over the last seven million years substantial megaherbivore extinctions occurred: 28 lineages became extinct, leading to the present-day communities lacking in large animals. These results highlight the great diversity of ancient megaherbivore communities, with many having far more megaherbivore species than exist today across Africa as a whole.

Human ancestors not to blame for ancient mammal extinctions in Africa
A fossil tooth of a hippo (Hippopotamus amphibius) (left) and a fossil tooth of a white rhinoceros (Ceratotherium simum) (right) , two of the few surviving megaherbivores, from the Late Pleistocene of western Kenya (left). Credit: J. Tyler Faith

Further analysis showed that the onset of the megaherbivore decline began roughly 4.6 million years ago, and that the rate of diversity decline did not change following the appearance of Homo erectus, a human ancestor often blamed for the extinctions. Rather, Faith's team argues that climate is more likely culprit.

"The key factor in the Plio-Pleistocene megaherbivore decline seems to be the expansion of grasslands, which is likely related to a global drop in atmospheric CO2 over the last five million years," says John Rowan, a postdoctoral scientist from University of Massachusetts Amherst. "Low CO2 levels favor tropical grasses over trees, and as a consequence savannas became less woody and more open through time. We know that many of the extinct megaherbivores fed on woody vegetation, so they seem to disappear alongside their food source."

The loss of massive herbivores may also account for other extinctions that have also been attributed to ancient hominins. Some scientist suggest that competition with increasingly carnivorous species of Homo led to the demise of numerous carnivores over the last few million years. Faith and his team suggest an alternative.

Early human ancestors not to blame for extinctions of giant African mammals
The decline of African megaherbivore diversity (gray curve) over the last seven million years was driven by falling atmospheric carbon dioxide and the expansion of grasslands, not ancient hominin impacts. The onset of the megaherbivore decline around 4.6 million years ago (red dashed line and shading) occurs well before the appearance of tool-bearing hominin species capable of hunting large prey. Credit: John Rowan
"We know there are also major extinctions among African carnivores at this time and that some of them, like saber-tooth cats, may have specialized on very large prey, perhaps juvenile elephants" says Paul Koch. "It could be that some of these carnivores disappeared with their megaherbivore prey."

"Looking at all of the potential drivers of the megaherbivore decline, our analyses suggest that changing climate and environment played the key role in Africa's past extinctions," said Faith. "It follows that in the search for ancient hominin impacts on ancient African ecosystems, we must focus our attention on the one species known to be capable of causing them—us, Homo sapiens, over the last 300,000 years."


Explore further

Teeth of Homo antecessor shed light on trends in Pleistocene hominin dental evolution

More information: J.T. Faith at University of Utah in Salt Lake City, UT el al., "Plio-Pleistocene decline of African megaherbivores: No evidence for ancient hominin impacts," Science (2018). science.sciencemag.org/cgi/doi … 1126/science.aau2728

R. Bobe el al., "The decline of Africa's largest mammals," Science (2018). science.sciencemag.org/cgi/doi … 1126/science.aav6883

Journal information: Science

Provided by University of Utah
Citation: Human ancestors not to blame for ancient mammal extinctions in Africa (2018, November 22) retrieved 17 June 2019 from https://phys.org/news/2018-11-human-ancestors-blame-ancient-mammal.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
343 shares

Feedback to editors

User comments

Nov 22, 2018
Evolution, like life, is competition. Humans do not need to differentiate themselves from the rest of the natural world. The ability of life to exist on this planet does not hang in the balance of what humans do. The world does not require saving, nor does it care. We could not eliminate life from this planet, no matter how determined to do so we might be.

Humans, however, are a much different thing to consider. We are fully capable of extincting ourselves, and the effects of our excretions on other living things are a great gauge to see how our future is being eliminated by our present actions.

Just a preemptive post for the anti-science trolls that are sure to jump on this article in their desperate race to somehow manufacture validation for their psychotic delusions.

Nov 23, 2018
Soon to be followed by the definitive study "Human ancestors are indeed to blame for ancient mammal extinctions in Africa"

Nov 23, 2018
Humans, however, are a much different... fully capable of extincting ourselves
Protohumans created technology. As soon as they developed the tech that enabled them to hunt the animals that were keeping their numbers in check, their pops exploded. Overpopulation became endemic and the constant conflict over resources ensued. And every new life-saving technology exacerbated the problem.

Protohumans congealed into tribes. Intertribal warfare became the norm. Those tribes which possessed greater internal cohesion combined with external animosity could be expected to prevail in competition. The victors would kill all the males and incorporate the females which accelerated our development.

This group selection quickly caused the human brain to grow to its present resource-hungry, unwieldy and unsustainable state. The unnatural demands of tribal life selected for increasingly unnatural behaviors.

IOW, it domesticated us.
Cont>

Nov 23, 2018
Tribalism continues to be the single most significant factor in human social behavior. In the struggle to prevail over other tribes, rulers discovered that religion and nationalism could be used to extend the tribal identity over ever larger groups and regions.

Rulers often met to discuss treaties in the attempt to reduce conflict. They quickly discovered that overpopulation was the real source of their problems.

Their records of food production and distribution showed them in no uncertain terms that overgrowth was inevitable and unavoidable. And when the people began to starve they would always blame the people in charge no matter how benevolent or well meaning they would be.

These rulers understood that the people were the real enemies of rulers everywhere. And so they began to manage them, to control their numbers by staging wars and revolts.

These Leaders intermarried and became a Tribe into themselves, dedicated to protecting the world from humanity.
Cont>

Nov 23, 2018
"16 For God so loved the WORLD that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life." JON3

-The world, not the people on it. This greatest of lies is followed by what these Leaders expect the people to do in return for it:

"17 For God did not send his Son into the world to condemn the world, but to save the world through him. 18 Whoever believes in him is not condemned, but whoever does not believe stands condemned already..."

-IOW, evil by definition. Over and over, all the holy books describe unbelievers as dishonest, indecent, and untrustworthy. And if you want to get all the rewards these gods promise then you will have to treat them accordingly.

This of course is the epitome of the tribal dynamic; internal empathy in conjunction with external animosity... internal amity, external emnity.
Cont>

Nov 23, 2018
This miraculous tool for managing pops has been used to create order out of chaos worldwide. An Empire, created by a Tribe of Leaders, dedicated ensuring a secure future for it's own decendents, and to preserving the greatest thing that humanity possesses - its accrued store of knowledge of how the universe works and how it can be used to our benefit.

Nov 23, 2018
Psalm 23 [ode to domestication]
1The Lord is [the Leaders are] my shepherd; I shall not want.

2 He maketh me to lie down in green pastures[Flanders field, gettysburg]: he leadeth me beside the still waters.

3 He restoreth my soul[necessary for immortality]: he leadeth me in the paths of righteousness for his name's sake[because unbelievers are evil].

4 Yea, though I walk through the valley of the shadow of death, I will fear no evil: for thou art with me; thy rod[punishment] and thy staff[control] they comfort me.

5 Thou preparest a table before me in the presence of mine enemies[to create a greater tribe] thou anointest my head with oil; my cup runneth over.

6 Surely goodness and mercy shall follow me all the days of my life: and I will dwell in the house of the Lord for ever."

-Leaders are only concerned with what you think and do while you are in this life. And They will promise you absolutely anything you could ever want in order to get you to comply.

Nov 24, 2018
]Protohumans created technology. As soon as they developed the tech that enabled them to hunt the animals that were keeping their numbers in check, their pops exploded.


That is not that the population genetic data show; modern chimps are still 10 times as many (and has 5 times the genetic variation) as the human bottleneck of ~10 k humans,

Also, your myths are irrelevant, even laughable, for the rest of us.

Nov 25, 2018
That is not what the population genetic data show; modern chimps are still 10 times as many (and has 5 times the genetic variation) as the human bottleneck of ~10 k human
And fully 10% of asians can trace their genes back to genghis Khan. Humans have a propensity for conquest. More capable tribes would systematically defeat other tribes and proceed to kill or enslave all the males and incorporate all the males.

We are aware of this process throughout recorded human history; there is no reason to assume that it didnt occur throughout the pleistocene as tribes developed crucial tech or improvements in social order and then used it to conquer whole regions.
http://rint.recht...rid2.htm

This would explain the homogeneity of the genome.

And yes it is logical to assume that one of these monumental breakthroughs would involve diplomacy, and of rulers colluding to solve their mutual problems by managing conflict.
laughable
Happy to entertain.

Nov 25, 2018
As soon as they developed the tech that enabled them to hunt the animals that were keeping their numbers in check, their pops exploded
-And this DOES explain how quickly humans spread throughout the world. Population pressure is the only explanation. Humans fled from endemic conflict. They were not the starry-eyed explorers eager to see over the next hill. They were running for their lives.

Any species will produce more offspring than can be expected to survive to maturity. Humans began unnaturally saving their offspring from early death through technology. This had never occurred before. And it happened so quickly that our reproductive rate didnt have time to adjust, as with seasonal breeders.

And then religions began to exploit this repro rate to the max.

The only way I can think of to explain why we havent stripped the entire planet bare, is Empire.

We were on course. A large swath from the Sahara to the gobi, stripped bare. And then it stopped.

Nov 25, 2018
Errata
"and proceed to kill or enslave all the males and incorporate all the FEmales."

Nov 25, 2018
As soon as they developed the tech that enabled them to hunt the animals that were keeping their numbers in check, their pops exploded
-And

Any species will produce more offspring than can be expected to survive to maturity. Humans began unnaturally saving their offspring from early death through technology. This had never occurred before. And it happened so quickly that our reproductive rate didnt have time to adjust, as with seasonal breeders.

And then religions began to exploit this repro rate to the max.

The only way I can think of to explain why we havent stripped the entire planet bare, is Empire.

We were on course. A large swath from the Sahara to the gobi, stripped bare. And then it stopped.
says SpookyOtto

Define what you mean by "Empire".

Do you have any children of your own??

Nov 26, 2018
Define what you mean by "Empire"
I defined it in detail further up in the thread. Why dont you reread it and concentrate this time.
Do you have any children of your own??
Probably. Why do you ask?

Nov 26, 2018
You said:
This miraculous tool for managing pops has been used to create order out of chaos worldwide.
An Empire, created by a Tribe of Leaders, dedicated ensuring a secure future for it's own decendents, and to preserving the greatest thing that humanity possesses - its accrued store of knowledge of how the universe works and how it can be used to our benefit.


The British Empire had the greatest form of government once the monarchy was essentially stripped of their traditional powers over the British people, which had been more of a dictatorship until the first Parliament convened. But, even then, the separation of Parliament into the House of Lords and the House of Commons did not produce an even disregard for social status, in spite of the House of Commons being the prime legislative body.

In comparison with the US Congress, which would you consider to be more for the people and less for the leadership? The monarch must approve all bills passed by Parliament

Nov 26, 2018
-contd-
There is no doubt that both Great Britain and the US government understand the value of informational resources and artifacts with as much, or more fervour as any other nation in history, which has been the cause for a wealth of museums, archives and other structures for the purpose of collecting, retaining, and preserving all pertinent materiel.
This process for collecting and preserving all historical materiel is celebrated throughout both nations, but in many other countries of the world, such actions are considered to be frivolous and of not much importance.
My question to you is: Despite the obviously unwanted attention by "first-world" researchers/scientists/adventurers towards collecting information/artifacts from stone-age tribes who have no desire to join 21st century societies and give up their "treasures" to such strangers, would you says that it is permissible and, indeed, vital for researchers to invade and "take" what they will in the name of science?

Nov 26, 2018
-contd-
Define what
I defined it in detail further
Do you have any children of your own??
Probably. Why do you ask?
says SpookyOtto

Read your link and wondered if you had children that you don't mind going off to war:
Of Malthus:
He regarded warfare in the earlier ages of the world as "the great business of mankind", and as one of the first causes and most powerful impulses of war "undoubtedly an insufficiency of room and food; and greatly as the circumstances of mankind have changed since it first began, the same cause still continues to operate and to produce, though in smaller degree, the same effects".


As you have been venting your dislike of the present number of world populations for years, would you be in favour of "wars and rumours of wars" to rid the Earth of its "excess" of humans, and would you, if you have or had children - consider your own children as a part of the "excess" of humans that should be gotten rid of - by necessity?

Nov 26, 2018
The British Empire had the greatest form of government
Like I say, no visible form of govt can withstand the onslaught of the unbridled tropical human repro rate. There are however ways to suppress it. For instance, fiefdom kept serfs on the verge of starvation. The Brits fought 2 wars to maintain the supply of opium into china, for slowing growth and for aiding in the destruction of that very recalcitrant culture. THAT Campaign is almost complete.

Like most constructs of Empire, the British 'empire' was purpose-built, intended to achieve certain objectives. And when it had served its Purpose it was dissolved, much like the USSR.
There is no doubt that both Great Britain and the US government
Again, purpose-built. Small chapters in a very large cookbook.

Interesting that the British aristocracy are the traditional inheritors of the throne of david. 12 tribes, 12 knights. Everything is symbol and metaphor to Leaders, our Shepherds.
Cont>

Nov 26, 2018
wondered if you had children that you don't mind going off to war
It is hard to grasp the concept 'human domestication'. The extent to which we have been bred to accept irrationalities such the finality of death.

We are taught that nothing is inevitable, not really. Religions have poisoned us with the idea that there are deities that can do absolutely anything we ask them to, if only our faith is strong enough. Matt7:7–8.

And so when someone posits the idea that overgrowth or war are inevitable, our minds are totally incapable of grasping what that means. It is an instinctive deflection.

I asked someone once if he believed in god. He said no. I then asked him if he believed in life after death and he said of course. But he had never made the connection that immortality depends on a god to make it happen.

War has always been inevitable. INEVITABLE. Ask Solomon. If you can somehow avoid it now you will only have to fight a worse one later on.
Cont>

Nov 26, 2018
"excess" of humans that should be gotten rid of
Pussytard - drama queen. More poison, more deflection. The tropical human animal evolved as slow, weak, defenseless creatures in an environment of maximum attrition. Individuals produced the most offspring and defended them with the most vigor, had the most successful bloodlines. They even went beyond what any animal had ever achieved, and began fashioning their own weapons - externalizing their evolution and using sharpened sticks instead of evolving fangs and claws.

Humans love their 20th child every bit as much as they love their first. And herein lies that great dichotomy - the more they produce and they more they protect, the more trouble they are in.

This is another reality that religion has bred us to ignore.

Domestication is far from absolute. The witches they burnt were actually the midwives who were teaching the ancient pagan arts of natural contraception and ABORTION.
Cont>

Nov 26, 2018
"There is a time for everything,
and a season for every activity under the heavens:

2 a time to be born and a time to die
a time to plant and a time to uproot...
a time to embrace and a time to refrain from embracing..."

-Pagan witches were burnt because colonies needed to be populated. Continents needed to be filled. And wars needed to be fought.

The greatest effects of war are not the number killed outright on the battlefield but the reduction in growth that they entail. The stress to displaced populations, the ruin of cropland, the fouling of the water supply.

Alexander's forces spent months marching up and down the Euphrates valley before they sacked Babylon, consuming crops, fouling streams and wells, and driving the populace off.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more