I had written on Peto's Paradox on a another cancer related thread before. However, Peto's Paradox is the evolution's answer to cancer prevention. The lack of correlation between body size and cancer risk is known as Peto’s Paradox. Animals with 1,000 times more cells than humans do not exhibit an increased cancer risk, suggesting that natural mechanisms can suppress cancer 1,000 times more effectively than is done in human cells. Though many potential reasons were proposed, it remained mostly unsolved.
You can see from the above that Elephants have a much lower cancer risk for its body mass.
The P53 Tumour Suppressor Protein
The p53 gene like the Rb gene, is a tumor suppressor gene, i.e., its activity stops the formation of tumors. If a person inherits only one functional copy of the p53 gene from their parents, they are predisposed to cancer and usually develop several independent tumors in a variety of tissues in early adulthood. This condition is rare, and is known as Li-Fraumeni syndrome. For a female with Li-Fraumeni, there's 100% breast cancer risk.
However, mutations in p53 are found in most tumor types, and so contribute to the complex network of molecular events leading to tumor formation.
The p53 gene has been mapped to chromosome 17. In the cell, p53 protein binds DNA, which in turn stimulates another gene to produce a protein called p21 that interacts with a cell division-stimulating protein (cdk2). When p21 is complexed with cdk2 the cell cannot pass through to the next stage of cell division. Mutant p53 can no longer bind DNA in an effective way, and as a consequence the p21 protein is not made available to act as the 'stop signal' for cell division. Thus cells divide uncontrollably, and form tumors.
What's different with the Elephant?
A few years ago, researchers found that elephants have 20 copies of the gene that encodes the p53 protein. Humans, in comparison, have just one. The protein essentially works like a copy editor, reviewing genetic material as cells multiply and potentially killing off cells with any damages that could lead to cancer. As elephants have multiple copies of the gene that encodes p53, they could have multiple rounds of "copy-editing," which could vastly reduce the risk of a damaged cell surviving.
But Why?
Scientists suggest that it's got to do with their testicles. Many male animals, including humans, have their testicles partially outside their body to cool them down, which is believed to be important for creating a healthy batch of sperm. Otherwise sperm DNA damage could occur due to high temperatures.
However, elephant testicles are located inside their bodies. As multi-ton, dark gray animals walking around in the sun, their testicles have the potential to get really hot — and therefore the elephants may have trouble making viable sperm. But if they had more copy-editing proteins, the theory goes, that hot sperm could be protected from damage..
It's possible that multiple copies of the p53 gene evolved to protect elephant sperm from hot temperatures. But it's also possible that those multiple copies evolved because elephants are big animals so are potentially more susceptible to cancer, or it could also be both things at once.
Other large animals don't have multiple copies of the p53 gene. Whales, for example, are large animals with internal testicles, but they seem to have just one copy. But whales also have an internal system to cool their testicles down, moreover, it doesn’t get as hot in the water.
You can see from the above that Elephants have a much lower cancer risk for its body mass.
The P53 Tumour Suppressor Protein
The p53 gene like the Rb gene, is a tumor suppressor gene, i.e., its activity stops the formation of tumors. If a person inherits only one functional copy of the p53 gene from their parents, they are predisposed to cancer and usually develop several independent tumors in a variety of tissues in early adulthood. This condition is rare, and is known as Li-Fraumeni syndrome. For a female with Li-Fraumeni, there's 100% breast cancer risk.
However, mutations in p53 are found in most tumor types, and so contribute to the complex network of molecular events leading to tumor formation.
The p53 gene has been mapped to chromosome 17. In the cell, p53 protein binds DNA, which in turn stimulates another gene to produce a protein called p21 that interacts with a cell division-stimulating protein (cdk2). When p21 is complexed with cdk2 the cell cannot pass through to the next stage of cell division. Mutant p53 can no longer bind DNA in an effective way, and as a consequence the p21 protein is not made available to act as the 'stop signal' for cell division. Thus cells divide uncontrollably, and form tumors.
What's different with the Elephant?
A few years ago, researchers found that elephants have 20 copies of the gene that encodes the p53 protein. Humans, in comparison, have just one. The protein essentially works like a copy editor, reviewing genetic material as cells multiply and potentially killing off cells with any damages that could lead to cancer. As elephants have multiple copies of the gene that encodes p53, they could have multiple rounds of "copy-editing," which could vastly reduce the risk of a damaged cell surviving.
But Why?
Scientists suggest that it's got to do with their testicles. Many male animals, including humans, have their testicles partially outside their body to cool them down, which is believed to be important for creating a healthy batch of sperm. Otherwise sperm DNA damage could occur due to high temperatures.
However, elephant testicles are located inside their bodies. As multi-ton, dark gray animals walking around in the sun, their testicles have the potential to get really hot — and therefore the elephants may have trouble making viable sperm. But if they had more copy-editing proteins, the theory goes, that hot sperm could be protected from damage..
It's possible that multiple copies of the p53 gene evolved to protect elephant sperm from hot temperatures. But it's also possible that those multiple copies evolved because elephants are big animals so are potentially more susceptible to cancer, or it could also be both things at once.
Other large animals don't have multiple copies of the p53 gene. Whales, for example, are large animals with internal testicles, but they seem to have just one copy. But whales also have an internal system to cool their testicles down, moreover, it doesn’t get as hot in the water.
