The average woman on Earth is born with an approximately 38% chance of developing cancer sometime in her lifetime. And the average man is born on our planet with about a 44% chance of developing cancer sometime in his lifetime.
Oxidative stress from the production of oxygen free radicals created during the metabolism of proteins, carbohydrates, and fats (food) appears to be the primary cause of cancer and aging amongst humans and other animals on Earth. But ionizing radiation from space and from the natural geology of the Earth and in the food we eat and the water we drink can also contribute to cancer and aging.
Ionizing radiation interacts with the tissue of humans and other animals by stripping away electrons from molecules, leaving behind chemically active radicals that can be harmful to the cells of the human body. As our civilization begins to expand off the Earth in the 21st century, the human species will encounter substantially higher levels of ionizing radiation from the cosmos. Enhanced exposure to Galactic Cosmic Rays (GCR) could significantly increase the rate of cancer and aging and even brain damage amongst explorers and settlers in the New Frontier-- unless appropriate means are utilized to mitigate the potentially deleterious effects of cosmic radiation and major solar events.