I think it's that a 10% chance of dying of cancer before old age is unacceptable to humans but won't have a big effect on population. Similarly, a 10% chance of

I think it's that a 10% chance of dying of cancer before old age is unacceptable to humans but won't have a big effect on population. Similarly, a 10% chance of birth defects isn't relevant to most species as a large proportion (often more than half) of their young die before adulthood anyway.