An illustration of Peto's Paradox. The solid red line indicates a relationship between cancer rate and (body mass)*(lifespan), and the dashed red line represents an approximation of the expected cancer rate. The solid blue line represents the observation that there is no relationship between cancer risk and (body mass)*(lifespan). For instance, cancer risk, which is 11-25% in the human population, is not vastly different between mice and humans. In contrast, cancer risk was estimated to be 5% in elephants. Cancer rates in whales are not known, but these models predict that 100% of the largest whales should have cancer by age 90, which is an unlikely scenario. Metastatic cancer was found in a duck-billed dinosaur fossil. While adult body mass is approximately the same for the dinosaur and the elephant, duck-billed dinosaurs are thought to have had a shorter lifespan. This suggests the trade-offs between reproduction and growth and cancer defense mechanisms left these dinosaurs more susceptible to cancer than elephants.