Why did mammoths become extinct?
The last mammoths were finished off by incest
Ekaterina Shutova, "Newspaper.Ru"The last mammoths on Earth left on Wrangel Island had to interbreed with relatives-freaks.
This is what finished off the last of their population, foreign researchers and their Russian colleague found out.
In 1993, Sergey Vartanyan, an employee of the State Nature Reserve and Candidate of Geological Sciences, discovered the remains of dwarf mammoths on Wrangel Island, whose height barely reached 1.8 meters. Using radiocarbon analysis used to determine the age of materials of biological origin, the staff of the Geographical Faculty of St. Petersburg University found out that mammoths lived on Wrangel Island until 2000 BC. Previously, it was believed that the last mammoths lived on the Taimyr 10 thousand years ago.
The discovery of the Russian candidate of geological Sciences showed that mammoths existed simultaneously with the Minoan culture in Crete, the Sumerian civilization and the eleventh dynasty of the Egyptian pharaohs.
Now Vartanyan is on a long expedition to Chukotka, and recently he took part in a new study together with scientists from the USA, Sweden and Canada. Thanks to him, scientists have found out how the last mammoths on Earth lived and, most importantly, what they died from. The results of the study can be found in the latest issue of the journal Current Biology (Palkopoulou et al., Complete Genomes Reveal Signatures of Demographic and Genetic Declines in the Woolly Mammoth).
To date, there are two main hypotheses of the extinction of "hairy elephants". The first is related to natural causes – climate change and deterioration of the food supply. The second is related to the human factor: according to many experts, mammoths were exterminated by hunters of the Upper Paleolithic – the period of the last glaciation, when people settled all over the earth. There are also quite extravagant assumptions – for example, that the relatives of elephants were killed by a comet that fell in North America. Some scientists are convinced that mammoths have become extinct due to a large-scale epidemic.
Anyway, it turned out that the reason for the extinction of the last surviving mammoths on the planet was the reduction of genetic diversity. Once on their last resting place – Wrangel Island, mammoths had no choice but to engage in inbreeding – closely related crossing, as a result of which anomalies, mutations and deformities increase. Incest among extinct animals led to the fact that the viability of each new generation was rapidly falling.
The researchers came to these results by fully reading the genomes of two mammoths. The first mammoth lived about 4,300 years ago on Wrangel Island and may have been one of the last mammoths on Earth, the second – 44,800 years ago in Northeastern Siberia (near Oymyakon). The analysis showed that the genes of a less ancient mammal show low genetic diversity and all the signs of living in a very small population, where relatives had to mate with each other.
After mammoths left the Eurasian expanses, their genetic diversity decreased by 30%. According to Lava Dahlen from the Department of Molecular Systematics at the Swedish Museum of Natural History, the genetic diversity of mammals trapped on Wrangel Island has not changed during the last 5,000 thousand years of the species' existence. Earlier, scientists found out that 500 to 1000 mammoths lived permanently on Wrangel Island.
"500 individuals is the minimum number limit in modern programs for the conservation of endangered animals," Dr. Dahlen notes.
The researchers also concluded that the woolly mammoth population was reduced for unknown reasons in the early or Middle Pleistocene – about 250-300 thousand years ago.
The Pleistocene is an epoch characterized by the diversity of the animal world: then the earth was inhabited by cave and marsupial lions, giant deer, diprotodons, the ancestors of modern camels and bears.
Scientists who participated in the study admit that working with ancient genomes is not an easy task. In most cases, DNA is very fragmented, damaged and contaminated with microbes and sedimentary rocks. But it is the genomes of extinct mammals that are the best source of information about extinct species and populations.
The team of researchers is going to continue working with genomes to further study the evolutionary history of the woolly mammoth.
"The genomes of extinct animals will not only help us better understand the biology and history of their species, but also shed light on the causes of extinction," Dr. Dahlen is sure.
Portal "Eternal youth" http://vechnayamolodost.ru24.04.2015