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Почему крупные звери редко болеют ракомIn the 1970-ies the British epidemiologist Richard Peto from Oxford noticed that the probability of cancer in large animals are no more than small ones. Meanwhile, everything had to be the opposite: the larger an animal is, the easier it is to get the tumor. This consideration seems logical, given the fact that all cells are about equally likely to transform into malignant. And if the large animal cells more, and tumors, they have to appear more often. This, however, is not observed, what Mr. Peter concluded that large animals have some anti-cancer mechanisms that are not small animals.

And since then, researchers have tried to understand what kind of mechanisms that protect elephants and whales from cancer. The question, as you can understand, has only vaguely evolutionary significance, because, who knows, maybe these mechanisms can be put at the service of medicine. Researchers from the Institute for development in Montpellier (France) made an attempt to describe the sustainability of large animals to cancer with the help of the mathematical model of dealing with different mutation strategies. It included a hundred variants of distribution of mutations over four thousand generations.

The model took into account two classes of genes is a proto-oncogene that can cause malignant transformation of cells, and tumor suppressors, responsible for repair of cells, so that it does not become suddenly due to damage in cancer. Accordingly, in order to "include" a cancer, you need to first genes are out of control, and the second - lost activity.

In an article published in the journal Evolutionary Applications, the authors write that the proto-oncogene and antioncogenes react differently in the evolution to increase body weight. The larger it is, the harder it is to activate the proto-oncogene. However, for low risk of cancer diseases has to pay a fee, and this is often reflected in the low fertility. The proposed model suggests that animals are medium in size are in a difficult situation: they have a lot of genes-suppressors of tumors, but their work is more expensive than the final benefit. Large animal can afford low fertility, as he has few natural enemies, but the animals of medium size are forced to prefer higher fertility than resistance to cancer. In the result of an evolutionary advantage in a species with an average size body belongs to those with mutations suppress the activity of tumor suppressors and as a result save energy and resources for reproduction.

The data helps to understand why people have cancer diseases occur in each of the third and whales, belugas - only 18% of the individuals. At the same time, the authors recognize that the number of proto-oncogene and tumor suppressors can be not the only reason why big animals rarely get cancer. For example, this can be explained by the fact that the big beasts of the lower level of oxygen radicals that damage DNA, as they generally have relatively low levels of metabolism.

Now researchers are busy comparison of the genomes of different animals, including elephants and humpback whales to confirm or disprove his theory. It should also be added that not all scientists generally recognize the existence of differences in the frequency of cancer between different species. This difference as add criticism may be due to the fact that, if the calculation does not take into account the age and other characteristics of the organism - in the sense that large animals on the slope years could get cancer no less of a person.

Based on the materials of Nature News.
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