[KMag]

> long before our current high rates of cancer

Be careful there. It's difficult to know historical base cancer rates, given recent advances in cancer detection. It's likely lots of cancer deaths in the elderly were simply chalked up to old age.

Also, every time DNA is copied, you roll the dice with cancer. Live long enough and you'll eventually get cancer. As people live longer, one expects cancer rates to increase, all else being equal. (Yes, there have been recent dips in life expectancy in the US, but over the time frame I'm presuming you're comparing with "our current high rates of cancer", the trend is still positive.)

Now, maybe cancer rates have increased due to increases in environmental carcinogens. However, it's not obvious to me that's the case.