Is cancer a price for a big brain?

Our big brain makes us superior to chimpanzees, but according to a new hypothesis, we may be paying for this size: that is the higher rate of cancer.

Chimp is thought to be the closest relative to humans in terms of evolution, we have up to 98% of the genome similar to chimpanzees. But for years, scientists have observed that chimpanzees have surprisingly low rates of cancer compared to humans.

To answer this, John McDonald, a researcher at Georgia Tech University, studied the genome of humans and chimpanzees.

Many previous studies have analyzed the differences in gene expression of humans and chimpanzees. McDonald and his colleagues reanalyzed the data of a previous study of gene expression and added excluded information.

They observed differences in gene expression in some tissues, including the brain, liver, testes and kidneys.

Cells self-destruct

McDonald wanted to verify the hypothesis that the difference in cancer rates between two species could be due to differences in the way cells self-destruct - this is an important biological process called programmed death. cell or apoptosis (cell cycle death).

The researchers found that some genes regulate the cycle-by-death mechanism expressed differently in humans compared to chimpanzees. The data show that human cells are not effective in carrying out cyclic death cycles like chimpanzee cells, at least in other studied brain cells and tissues.

So what is the cell cycle death associated with cancer?

Reduced cell death cycles are associated with increased risk of cancer. At the same time, some genes that regulate this cycle are also thought to have malfunctioned in cancer cells. This means: cancer cells divide blamelessly, somehow they reject the signals that dictate the process of self-destruction.

Cancer is the price to pay for the big brain. (Photo: spacesuityoga )

Bargain

So what does this have to do with a big brain? In the course of human evolution, it is thought that people are naturally chosen because of their large brains and superior cognitive abilities. At the same time, there is another theory that to get a bigger brain than another species, we need to have a high rate of neuron production.

Researchers are linking the two hypotheses together. They think that reduced cell cycle death may have helped people get a large brain size. But it also makes us more likely to get cancer.

McDonald said: 'It is difficult to explain why we evolved to have a less efficient cyclic system. So the hypothesis we are examining may be that increased brain size is what puts the selective pressure on the system to reduce the cell's self-destruct cycle. ' He also added that although the self-destruct cycle may mean higher risk of cancer, there is no selective evolutionary pressure that has a negative impact on it by most diseases. Cancer appears only after the reproductive age.

The above hypothesis is quite different from many of the previous views about the path of our great brain evolution. McDonald's said: 'People have bigger brains than chimpanzees, most of us focusing on the fact that our brains may be producing neurons at a faster rate. But I think the flip side of the story is that we can completely destroy them. '

This study is supported by recent studies. They observed that people with certain cognitive diseases - diseases associated with increased neuronal destruction - had lower rates of cancer.

Additional research is required

So far, published evidence has been obtained from the genotype of the gene. Other studies are underway to analyze the cell death rate in chimpanzees and humans. Even if there is more evidence, no one can know for sure why we evolved that way.

Stephen Hubbell, an evolutionary biology professor at UCLA, who is not involved in the study, said: 'It is a hypothesis, so the question is whether it is correct or not. It would be interesting if the choice for humans changed the expression of these genes and impacted our risk of disease. '

He added: 'I think this really provoked interesting research in the direction in which evolutionary biology was born to answer medical questions'.

The research results are published online in Medical Hypotheses.