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The Age of Genomes
Steven Lipkin
More books on Evolution
Our bodies have at least seven different ways of protect our genome against the many and diverse threats it faces every day.
We exist bc, 2 billion years ago, bacteria evolved ability to photosynthesise the sun's rays to make energy, with oxygen as a by-product. Oxygen is a highly unstable, toxic chemical that can damage DNA, as well as proteins and lipids. We use this destructive power of oxygen to break down molecules storing energy to provide us with fuel. To protect ourselves from dangeroeus side effects of oxygen, bacteria, plants, insects and humans have evolved a restorative pathway called DNS base excision repair, which fixes the damage from the oxygen-caused mutations that constantly arise in our bodies.
Our lower intestines have high levels of sulfur, which can corrode gut tissue.To cope with that, cells lining stomach turn over every few days. Every time a cell divides, there is a chance of mutation caused by the sulfur stress, and thus chance of cancer.
There are also genes impt for repairing damage from environmental stress. There were whole families who for generations were prone to develop stomach cancer. But after widespread adoption of refrigerators in mid C20, family members went back to 'normal' numbers of cancers. Explanation: meat used to be preserved by smoking and curing. But smoking changes some of the proteins in the food, producing damaging chemicals.
200 years ago, lung cancer was rare. Today it is the leading cause of cancer death. Tracks the introduction of cheap cigarettes. (But only 1 in 7 long term smokers develops lung cancer).
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