Ancient DNA adds extra millennia to mammoths


It used to be thought that mammoths died out about 10-12 thousand years ago, but recently we are increasingly hearing that they actually lived longer. The previous figures were obtained when the age of the mammoth remains was determined. Now, researchers have learned how to analyze ancient DNA, which is extracted from thousand-year-old bones and even just from the earth.

Thanks to ancient DNA, it was possible to learn a lot of new things about prehistoric people and animals; for the study of Neanderthals and Denisovans on their DNA this year they were given the Nobel Prize, and in the article about it, by the way, we also remembered mammoths, which seemed to have died out later than it was thought. According to some estimates, they could be found in Siberia only about four thousand years ago.

However, with ancient DNA, things may not be so simple. After all, where does DNA come from in the soil or in sedimentary rocks? From exfoliated cells, from waste products, and when a living organism dies, then from its remains – for example, from bones. Bones lie and slowly disintegrate, leaving behind pieces of DNA; these pieces can then be read. And here the question arises: how long can the bones donate their DNA, or, in other words, how long do they break down?

It all depends on the climate and soil properties, but in general, in warmer latitudes, bones crumble in a few decades. That is, if we find ancient animal DNA, we can be sure that the remains of the animal to which it belonged were here, by geological standards, quite recently. The age of the DNA itself will correspond to the age of the geological formation where it was found, and this age will approximately correspond to the time when the animal was still alive.

But in the subpolar latitudes, bones can be destroyed for a very long time, up to several thousand years. In this case, the age of the DNA does not correspond to the lifetime of a mammoth or, for example, a woolly rhinoceros, but to the time when their bones finally crumbled. Those extra thousands of years that mammoths have appeared, in fact, may be the duration of the “life” of their remains, slowly decaying in Siberia or Canada.

Employees of the University of Cincinnati and the University of Colorado at Boulder, who describe in Nature this possible incident with ancient DNA, support their reasoning with the results of radiocarbon analysis of the bones of various animals. For example, in Norway they found deer antlers about two thousand years old, and in the Antarctic they found the remains of sea elephants five thousand years old. Yes, and the bones of the mammoths themselves, after all, somehow also survived to our time.

But still, when they analyze ancient DNA, they mean not only its age. Researchers who extended the life of Siberian mammoths wrote in Nature a response saying that their mammoth DNA shows quite low genetic diversity. And low diversity means the population is on its way to extinction. In addition, plant DNA from the same central and northern regions of Siberia indicates that mammoths lived in their usual tundra-steppe landscape. That is, the environment still suited them, but they had already begun to die out. If there is indeed a DNA age error, then Siberian mammoths should have lived when they were doing well, and the DNA itself should have been more diverse.

Perhaps the timing of the extinction of prehistoric animals, which are determined only by DNA, is indeed too close to us due to the slow decay of bones. But, most likely, mammoths and others really died out later than it was determined only from their remains. Well, exactly how much later remains a matter of dispute.


Source: Автономная некоммерческая организация "Редакция журнала «Наука и жизнь»" by www.nkj.ru.

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