There are more than 100 types of cancers that affect millions of men and women. But, do animals suffer from cancer?

Research has found cancer that affects wild animals like the Tasmanian devil facial tumor disease, sea turtle fibropapillomatosis and sea lion genital carcinoma and that human activities have contributed to development of these cancers. However, the prevalence of cancer among humans is thought of being higher than animals.

A new research has shown why chimps, our closest cousins, don't develop as many cancers as we do.

Chimps and humans share about 96 percent of our DNA and it is the four percent that accounts for the difference in cancer rates among chimps and humans.

Researcher Soojin Yi from Georgia Tech analyzed brain samples of humans and chimps to find that certain modifications in the DNA structure raises the risk of cancer in humans.

"Our study indicates that certain human diseases may have evolutionary epigenetic origins. Such findings, in the long term, may help to develop better therapeutic targets or means for some human diseases," said Yi, a faculty member in the School of Biology.

The modification called methylation doesn't change the genetic structure of the DNA but alters the way it is expressed. DNA methylation represses gene expression or puts it in 'off' mode.

Yi and her research team collected samples from the pre-frontal cortex of the brains of human and chimpanzees. They then generated genome-wide methylation maps of the brains. They found lower levels of methylation in human brains than chimps.

They also found that most of the genes that had low levels of methylations were the drivers of protein binding and cell metabolism. Researchers say that this explains why we are particularly susceptible to certain diseases.

"This list of genes includes disproportionately high numbers of those related to diseases. They are linked to autism, neural-tube defects and alcohol and other chemical dependencies. This suggests that methylation differences between the species might have significant functional consequences. They also might be linked to the evolution of our vulnerability to certain diseases, including cancer," added Yi.

The study was published in the American Journal of Human Genetics.