Big animals have higher cancer risk – but also evolved better defences

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Big animals have higher ******* risk – but also evolved better defences

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African elephants have extra copies of genes that help resist *******

Neil Aldridge/Nature Picture Library/Alamy

******* animals live longer and have more cells that could go awry, so we would expect them to have a greater risk of developing *******. A comprehensive analysis of 263 species suggests this is indeed the case, but also finds that some large animals have evolved ways to curb the risk.

“We provide the first empirical evidence to show that there’s an association between body size and ******* prevalence, meaning that ******* species get more ******* than smaller species,” says

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at University College London.

The results stand in contrast to prior studies that have found

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. But many of these involved just a few dozen species, says Butler.

To gain a broader view, Butler and his colleagues analysed data on the size and ******* rates of 79 species of bird, 90 mammals, 63 reptiles and 31 amphibians. This data came from previous work by other researchers, who had sifted through autopsy records that logged whether captive animals – kept in places like zoos and aquariums – had ******* when they died.

The team found that larger animals were slightly more likely to have ******* at the time of their death compared with smaller ones. Across birds and mammals, every 1 per cent increase in body mass was linked to a 0.1 per cent increase in ******* rate, on average. Body mass data wasn’t available for reptiles and amphibians, so the team used body length, finding that every 1 per cent increase was linked to an average rise in ******* rate of 0.003 per cent.

Butler and his team say their findings challenge a long-standing idea known as Peto’s paradox, which points out that ******* rates should correlate with body size but don’t. On the other hand,

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at the University of Rochester in New York state says the weakness of the correlation still demands explanation.

“The increase in risk they see is very, very minor, and it’s just not proportional at all to body size,” she says. “If you take a small animal like a mouse, and a human is maybe 100 times *******, or an elephant is 1000 times *******, the difference in ******* rate is not 100 times higher in humans, or 1000 times higher in the elephant.”

That suggests larger species have evolved more ways to protect themselves, says Gorbunova.

Indeed, by using evolutionary trees to infer animals’ rates of body size evolution, the team found that bird and mammal species of similar size had better defences against ******* if they had experienced a more rapid increase in size during their evolution.

Previous studies have pinpointed genetic adaptations in elephants and whales that may protect against ******* by improving DNA repair or stopping faulty cells from dividing.

A deeper understanding of how some animals resist ******* could lead to new therapies for people, says Gorbunova. “If you find out that, in these *******-resistant animals, there are particular biological pathways that are tweaked differently, we could also design, for example, small molecules that would target these pathways and then either kill ******* cells more efficiently, or maybe even prevent ******* from occurring,” she says.

“These would be likely to be very promising drugs because, in the course of evolution, those mechanisms have been tested over millions of years,” she says.

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