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Despite decades of research, scientists were still trying to figure out why rates of malignant cancer do not appear to increase with an animal species' size – a paradox first proposed in 1977 by Richard Peto.

A new study may have just put the paradox to rest, finding larger species like giraffes and pythons do have higher cancer rates than smaller ones like bats and frogs after all.

The results did find a curious link between repeated jumps in body size in a species' history and a reduction in tumors and malignancies.

Cancer is typically caused by gene mutations in cells leading to uncontrolled cell division. It would make sense for animals with more cells to have a greater chance of a cancer-causing mutation. Since larger animals tend to have longer lifespans, that risk should grow with time. Yet studies kept failing to find this.

University College London computational biologist George Butler and colleagues suspect this trend was missed for so long because not enough samples of each species were drawn on in the studies probing it, which also relied on methods that biased results, confounding the high level of variation between individuals in a species.

Using a different statistical approach that avoided this bias, Butler and team found the long-elusive but expected trend in terrestrial animals by examining 263 species of amphibians, birds, mammals, and reptiles, and pooling their cancer prevalence data before analyzing it.