In the 1970s, scientists realized that larger animals should suffer more from cancer. And that was not the case

Cancer is one of the most dreaded diseases of mankind. However, it is a disease that also affects animals. By studying cancer in animals we realized a strange paradox: contrary to what we expected, cancer does not affect large animals more than small animals.

number question Cancer arises from cells that fail and begin to reproduce uncontrollably. If we get mathematical, the calculation is simple: the higher the number of cells, the higher the probability of developing cancer. This probability should also increase with time: the more time passes, the more likely the cell will fail.

draw like a lottery, explained to the British press guardian Zoological Society of London veterinary pathologist Simon Spiro. So the life expectancy of an elephant should be much less than that of a human. The problem is… it doesn’t.

The case of whales is even more significant. It is estimated that if we apply the probability of “failure” of a human cell to the number of cells in a whale, their lifespan will be less than a year. However, these cetaceans can reach 200 years old.

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Peto’s paradox. We call this phenomenon Peto’s paradox in honor of Richard Peto, professor of medical statistics and epidemiology at the University of Oxford, who pointed out the discrepancy between theory and practice in this context in the 1970s. Peto observed that the relationship appears to be rather inverse: the larger the size, the less likely to develop the disease.

A hidden variable. But the probability of developing cancer is not merely a function of time and numbers. Cancer has an important genetic component. And it is in genes where scientists have found the solution to this paradox.

Spiro and his team studied dead animals at London Zoo. Their goal: to know how often their cells mutate, that is, how often their DNA changes. They found that there is a very precise inverse relationship between longevity and the frequency of these mutations: the more mutations per year, the shorter a species’ life.

At this point very different species have presented the same number of mutations throughout their lives. For example, a mouse can accumulate about 3,200 mutations during its four-year life at a rate of 400 mutations per year. However, a human accumulates about 3,760 mutations over his 80-year life, at a rate of 47 per year.

P53. Turning to elephants, two recent studies, one from the Université Autónoma de Barcelona’s Institute of Biotechnology and Biomedicine, and the other As noted by the University of Chicago and the University of Utah, a single gene holds many answers: One is called p53. So much so that it has earned the nickname “Guardian of the Genome”.

This gene may be behind the self-repairing ability of DNA in this species. This gene will prevent cellular mutations such as those behind the emergence of cancer. This is where the numbers work in elephants’ favor: if humans have one copy of this gene, pachyderms have twenty.

A normal concern. Cancer is one of the diseases that has attracted the most attention in the 20th century. This is no coincidence: with the sharp decline in mortality from infectious diseases, humans have crossed this other limit to their longevity.

This interest is why understanding cancer in animals is so important: the better we understand it, the easier it will be to find a cure. Or at least therapies that reduce the risks associated with the disease.

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Picture | Bering Land Bridge National Preserve, CC BY-SA 2.0