This is pure speculation, but maybe it's beneficial in some circumstances to make way for the younger generation? Natural selection doesn't necessarily favor g

This is pure speculation, but maybe it's beneficial in some circumstances to make way for the younger generation? Natural selection doesn't necessarily favor genes that optimize the health of a particular animal. Natural selection favors genes that optimize for more copies of themselves, at whatever cost to their current carriers. Perhaps under some scenarios of canine evolution, the fittest genes might have been ones that selected for higher turnover than would happen if bodies wore out naturally.