For years, scientists have debated whether humans or the climate are responsible for the dramatic decline in large mammal populations over the past few thousand years. A new study from Aarhus University confirms that climate cannot be the cause. About 100,000 years ago, the first modern humans migrated out of Africa in large numbers. They are very good at adapting to new habitats, from deserts and jungles to the icy coniferous forests of the far north, and they have settled in almost every landscape.
Prehistoric humans are attacking an elephant. New research suggests that it was humans, not the climate, that caused the dramatic decline of nearly all of Earth's megafauna 50,000 years ago. **First published in Bryant & Guy, 1883. e.Wood carvings by Bayard.
Part of the reason for this success is the ability of humans to hunt large animals. With ingenious hunting skills and specially crafted **, they have mastered the art of killing the most dangerous mammals perfectly. But unfortunately, the great success of our ancestors came at the expense of other large mammals.
It is known that many large species went extinct during the global colonization of modern humans. Now, according to a new study from Aarhus University, the large mammals that survived have also experienced a sharp decline.
The eastern gorilla is one of the mammals with the largest population decline. Today, it lives in only a small area of the Democratic Republic of the Congo. Source**: michalsloviak
By studying the DNA of 139 extant large mammals, scientists have found that almost all species declined dramatically about 50,000 years ago.
Jens-Christian Svenning, director of the Centre for Novel Biosphere Ecodynamics (Econovo) and professor at Aarhus University, is the initiator of the study.
Another large mammal whose numbers have plummeted is the great one-horned rhinoceros. It lives in India and is one of the only five remaining species of rhinoceros. **mayank1704
We studied the evolution of large mammal populations over the past 750,000 years. For the first 700,000 years, the population was fairly stable, but 50,000 years ago, the curve broke and the population declined dramatically, never recovering. Over the past 800,000 years, the world has fluctuated between glacial and interglacial periods approximately every 100,000 years. If climate is the cause, then we should have seen even greater fluctuations when the climate changed 50,000 years ago. But we didn't see it. Therefore, humans are the most likely explanation. "
For decades, scientists have debated why large mammals have gone extinct or rapidly declined over the past 50,000 years. Scientists believe that rapid and violent fluctuations in the climate are the main cause. For example, they believe that the reason for the extinction of the woolly mammoth was the disappearance of the cold mammoth grasslands. On the contrary, there are some people who believe that the prevalence of modern humans (Homo sapiens) is the main reason. They believe that our ancestors hunted these animals so that they were either completely extinct or largely wiped out.
By far the most important evidence in the debate is fossils dating back 50,000 years. These fossils show that the strong, selective extinction of large animals in time and space roughly coincides with the global spread of modern humans. As a result, the extinction of animals is hardly linked to climate. However, the debate continues.
The new data provided by the new study sheds new light on this debate. By studying the DNA of 139 species of large mammals, researchers can see that their numbers have also declined over the past 50,000 years. This development appears to be related to human transmission rather than climate change.
The Taal sheep is closely related to the goat, but is actually a type of antelope. It lives in the mountainous regions of southern India and its population used to be much larger. **ameshshenai
Over the past 20 years, there has been a revolution in the field of DNA sequencing. Mapping the entire genetic spectrum has become easy and inexpensive, and as a result, the DNA of many species is now mapped.
Juraj Bergman, an assistant professor at Aarhus University and the lead researcher of the new study, explained that the genetic profiles of species around the world are freely available on the Internet, and that the Aarhus team used the data.
We collected data on 139 species of large mammals and analysed a large amount of data. There are about 3 billion data points per species, so it takes a long time and a lot of computing power: DNA contains a lot of information about the past. Most people know about the Tree of Life, which shows how different species are developing and what common ancestors they have. We've done the same with DNA mutations. By grouping mutations and building a family tree, we can estimate the population size of a particular species over a period of time. The larger the population of an animal, the more mutation occurs. It's actually a simple math problem. Take elephants, for example. There is a chance that an elephant will have some mutations every time it becomes pregnant, and these mutations will be passed on to their offspring. More births mean more variation"。
As shown in the picture, the Pere Davide elk no longer live in the wild. Today's only remaining animals live in zoos and animal parks. Tim Firth.
The 139 species of large mammals examined in this study are all species that exist today. These include elephants, bears, kangaroos, and antelopes, among others. It is estimated that there are 6,399 species of mammals on Earth, but this study selected 139 species of megafauna that exist to examine how their numbers have changed over the past 40,000 to 50,000 years, when similar macrofauna became extinct.
Large mammals are also known as megafauna – defined as animals that weigh more than 44 kilograms in adulthood. As a result, humans are also seen as megafauna. In this study, though, the researchers looked at species that weighed only 22 kilograms, so every continent was represented except Antarctica.
In the water is the forest antelope. This is an antelope that lives in many countries in Africa, and the forest antelope lives in swampy areas and used to be more abundant. **kennyannydenny
However, the size of the elephant population is not the only factor influencing the number of variations.
If the area where the elephant lives suddenly dries up, these animals become stressed, affecting the composition of the variation. The same effect can occur if two isolated elephant herds suddenly meet and mix genes.
If it's not just the size of the population that affects the amount of variation, you would think the results are inconclusive. But that's not the case, explains Yuraj Bergman.
Only 10% of the mammalian genome is active genes. Selective pressures from the environment or migration will mainly lead to genetic mutations. The remaining 90% of genes are neutral, so we looked at mutations in the parts of the genome that are least susceptible to environmental influences. These sections mainly illustrate the size of the population over time. "
The Himalayas are inhabited by takin. It lives in bamboo forests and feeds on fresh leaves and grass. 50,000 years ago, takin populations were largely extinct. Fact**: Eric Kilby.
Much of the debate about what causes the extinction or decline of large animals has focused on woolly mammoths. But this is not a good example because, as Jens-Christian Svenning explains, most extinct megafauna species are associated with temperate or tropical climates.
He said:"The classic argument for climate as an explanatory model is based on the fact that when the ice melts and habitat types disappear, woolly mammoths and a few others that do not work with the so-called"Mammoth Prairie"The associated species have disappeared with it. This is essentially an unsatisfactory mode of explanation, as the vast majority of extinct megafauna species at that time simply did not live in the mammoth grasslands. They live in warm regions such as temperate and tropical forests or savannahs. In our study, we also found that during this period, the number of many surviving megafauna species, which came from a variety of different regions and habitats, declined dramatically"。
The final end of the debate may not have been determined, but Jens-Christian Svenning argues that the debate over climate as an explanation is difficult to continue.
It seems inconceivable that it is possible to propose a climate model that would explain why all continents and large fauna have experienced extinction and continuous decline since about 50,000 years ago. Over the past 66 million years, this selective extinction of megafauna has been unique, despite the enormous climate change. "
Given the abundance of data we now have, it is also difficult to deny that, on the contrary, it is due to the spread of humanity from Africa to the globe and the subsequent growth of the population.
Compiled from: scitechdaily