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Elephant rarely get cancer, their testicles could tell us why

Early studies into cancer brought about the hypothesis that larger, long-lived animals would be more likely to get cancer than smaller, shorter-lived ones. The thought behind this theory was simple: the more cells you have and the longer they have to mutate, the greater the likelihood of an accumulation of cancerous mutations.

The theory, however, didn’t, doesn’t, stand up. Neither the land nor the ocean’s largest mammals, elephant and whales, get cancer frequently. In fact, amongst both of these species, cancer instance rates are very low.

These findings resulted in what is known today as Peto’s paradox. Despite the clear logic behind the early theories as to which species should experience cancer the most, no clear correlation, between size and length of life and proneness to cancer, exists.

Why elephant rarely get cancer

With regard to elephant, scientists think they may have found evidence suggesting as to why cancer is so infrequent. In many animals, a gene called TP53 is observable. It is known for its ability to repair DNA damaged in replication.

The TP53 gene prevents the development of tumours by pausing the replication of mutated cells and either signalling for the repair of the mutated cells or, if the damage cannot be repaired, initiating their destruction. In more than half of all human cancers, the TP53 gene’s function has been lost through random mutations.

Humans, and indeed most animals, have one copy of this gene; that one gene is capable of producing 2 different proteins used in the body’s response to mutating cells. Elephant have an abnormally high 20 copies of this gene and each of these copies has two allele variations.

An elephant’s 20 TP53 copies are capable of producing 40 different types of protein. This means that not only are elephant better covered if one of their TP53 genes loses its function, but the different variations of the TP53 genes respond to damaged cells differently. The Scientific American’s coverage of this finding suggests that this “likely gives [elephant bodies] an edge when detecting and weeding out mutations.”

The elephant’s hot testicles as explanation for its robustness against cancer

Elephant have incredibly hot testicles. The African elephant has evolved in some of the warmest, year-round habitats on the earth. Despite that elephant have many adaptive traits that have allowed them to live in environments such as Tsavo, they are still huge, thick-skinned animals living often under the equatorial sun.

What’s more, elephant testes are found entirely inside their body. This means that the temperature of their testicles is the same as the temperature of their core.

The advantage of having scrotal testes – distended outside of the body – is that the testes are kept away from the body and can therefore be kept at a slightly cooler temperature. Keeping the testes between 2-4 degrees Celsius below core temperature is essential if mammals are to produce healthy sperm.

Despite being host to what would be considered a dangerously warm environment for sperm production in other mammals, male elephant do produce healthy sex cells. University of Oxford professor Fritz Vollrath suggests that the reason elephant are capable of this may be because of TP53.

Vollrath hypothesises that the elephant’s TP53 cells are an adaptive legacy of their evolution in hotter environments. The hypothesis requires testing. However, core to this investigation is the working belief that the elephant’s warm testicles resulted in the necessity of a more comprehensive and varied TP53 influence.

That elephant are more resilient to the developments of cancers is, if this hypothesis is true, a side affect to the elephant’s response to sperm safe-guarding.

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