The Circle of Life

Fact: Elephants never get cancer.

The cure for cancer? Look to the natural world for answers, as it seems that elephants have cracked the secret to eternal life.

Cancer is simply uncontrolled cell division, which occurs when the DNA of a cell becomes damaged. DNA damage occurs most commonly when cells divide, and if this damage leads to the inactivation of particular genes (known as tumour suppressor genes) it can lead to the development of a cancer.

Larger animals are made up of a greater number of cells and tend to live for a very long time, meaning their cells must undergo a larger number of divisions throughout their life. Therefore logic dictates that elephants should have higher rates of cancer than us – but they don’t. In fact, they almost never get cancer. Welcome to ‘Peto’s paradox’.

As far as paradoxes go, this one is easily solved. P53 is a critical tumour suppressor gene that stops cells becoming cancerous by causing them to die if any DNA damage occurs. One working copy of P53 alone is enough to kill a damaged cell, but humans only have two copies of P53 – one from each parent – and so in old age its relatively common for both copies to become damaged in a single cell, allowing that cell to develop into a cancer.

Elephants, however, have at least 40 copies of P53 in each cell. This means that it is incredibly rare for all those genes to become damaged in a single cell, and so throughout their lives any elephant cells that have damaged DNA will be killed by the P53 response, rather than being allowed to live and develop into a cancer.

It’s funny to think just how brutal the immune system is: any cell that is even slightly abnormal is immediately killed for the greater good. You’re just one big microscopic dictatorship.

‘Another one of Mr Shaunak’s Little Bites of Science’
Image under Creative Commons license, in the public domain.

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