If human beings are willful for hundreds of years, the largest land animals or cattle.

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 If human beings are willful for hundreds of years, the largest land animals or cattle.


Photo: the woman is looking at the skeleton of mammoth throughout history. Humans always selectively kill the largest mammal. But in the late Pleistocene, about 125000 years ago, these giant animals began to disappear. Now, they are all extinct. The reasons for the extinction of these giant mammals have been studied and discussed in depth, but the latest research in University of New Mexicos FelisaSmith is that the responsibility is entirely attributed to human and our close relatives. By observing the changes in the size of mammals over time, Smith and her colleagues have shown that when human beings appear, the rate of extinction of mammals accelerated by 100 to 1000 times. This is not a new discovery. Many scientists including Smith have discovered the same trend in Australia and America. But new analysis shows that this pattern occurs on all continents except Antarctica, and runs through at least the past 125 thousand years. Smith said: selective extinction is an important sign of human activities. In other words, when humans began to rise, large animals began to accelerate extinction. Edewitt Jucal, of George Mason University, said: it doesnt take much time to destroy a species. AdvaitJukar Human beings do not need to go out to kill all the members of this species. All we have to do is to pressure the number of their populations and to keep the fertility rate at a low level by putting enough hunting pressure on it. In the end, the whole species will collapse. The size of species is usually related to the geographical area of their existence. Africa is smaller than Eurasia, but larger than the Americas, so the animal shape is also in between. But when humans came out of Africa, the average mammal size was 50% smaller than that of Eurasia or the Americas. For this reason, Smith believes that this type of collapse has begun before the rise of the Homo sapiens, which can be traced back to the age of the rise of the erectus 1 million 800 thousand years ago. Smith said: this indicates that humans are beginning to turn from a large number of plants to meat, and becoming a good predator is a universal characteristic of human beings. When the Neanderthal (Neanderthals), the Danny (Denisovans) and the modern people spread in Europe and Asia, the average number of mammals there was reduced by half. When Homo sapiens later came to Australia, the average size of mammals there was reduced by 10 times. When early humans finally entered the Americas with effective long range weapons, they pushed the mammal size there to shrink. About 15000 years ago, the average weight of mammals in North America dropped from 98 kilograms to 7.7 kilograms. This is not a general feature of mammalian evolution. Smiths colleague, Nebraska - Lincoln Universitys Catherine Lyons (KathleenLyons) has been collecting data on the shape of mammal changes over the past 65 million years. Her data show that in the past millions of years, the biggest beast is very easy to die out. Smith said: people think that large animals are more vulnerable. But large animals also have a larger geographical area, which can help them avoid extinction. For most animals, most of the time, large body is a good thing. Large mammals are not particularly susceptible to climate change, including several ice ages and warm periods. For Smith, this should help solve the long debate over whether human beings are responsible for the extinction of large animals. Smith said: when the climate gets warmer or colder, no matter bigger or smaller mammals, they can not escape the influence. Only when human beings participate in it will greatly increase the risk of extinction of large animals. However, even if climate change is not the main cause of the past killing of large mammals, three things are now completely different: 1) the climate is changing at an alarming rate; 2) this change is affected by human behavior; 3) human beings have led to a growing space for the survival of wild animals. In the past, large mammals could migrate to cope with rising temperatures and rainfall. But now, cities, farms and roads have blocked their way. These changes mean that modern humans have become accustomed to killing medium and small mammals, which have changed the trend of animal shape for thousands of years. Our ancestors hunted mammals by hunting. Now, we can indirectly guide them to extinction by narrowing their habitats or introducing unfamiliar predators. Even now, the largest mammal is still in the most serious danger. Most large mammals live in countries with the least resources, many of which are in a state of violent conflict. African elephants were heavily poached. Only two female rhinoceros were found in the North white rhino. Even in giraffe, its population decreased by 40% in just 30 years, and it was listed in the red list of endangered species last year. Everyone may think that these iconic animals are still large, but in fact their population is quite fragile, and its terrified, Smith said. The extinction of giant animals is a tragedy in itself, but it will also destroy the world. For example, elephants and their close relatives are very good at protecting trees from the erosion of grassland. As mammoths disappear from the northern hemisphere, the forests and the grassland world they maintain have disappeared. We think the modern ecosystem is normal, Lyons said. But in fact, this idea is flawed and it doesnt work as it did 11000 years ago. Smith calculates that if all threatened species are eventually extinct, the largest mammal on land will be domesticated cows. To a great extent, all this is due to what human beings do. (small) source of this article: NetEase science and technology report editor: Wang Fengzhi _NT2541 The extinction of giant animals is a tragedy in itself, but it will also destroy the world. For example, elephants and their close relatives are very good at protecting trees from the erosion of grassland. As mammoths disappear from the northern hemisphere, the forests and the grassland world they maintain have disappeared. We think the modern ecosystem is normal, Lyons said. But in fact, this idea is flawed and it doesnt work as it did 11000 years ago. Smith calculates that if all threatened species are eventually extinct, the largest mammal on land will be domesticated cows. To a great extent, all this is due to what human beings do. (small)