Generally, larger mammals live longer than smaller ones. However, new research examining the link between growth and mortality has shed light on why large breeds of dogs die at a younger age than small breeds of dogs. Scientists found that large breeds age at a faster rate. This speed increases the risk of death for bigger dogs. They found that among breeds of dogs, an increase of 4.4 pounds leads to the loss of roughly 1 month of life expectancy. The accelerated rate of aging could also explain why big dogs get cancer more often than small dogs. See more at Live Science.