In the wild, most mice do not live past 6 months, because of predators, cold, and starvation. In protected environments, mice live 2-3 years (max life span of 4 years - 1). They start showing signs of aging at one and a half years of age. There are a number of similarities between mice and humans: 

• Almost 99% of mouse genes resemble the genes from the human genome (3)
• Mice and humans have overlapping aging proteins (4).
• Mice and humans have similar molecular and cellular processes (5)
• Cancers in mice have similar pathology to those in humans (5)
• Aging mice have many of the same diseases of humans (6, 7): Cancer, heart disease, arthritis, chronic kidney disease, cataracts, osteoporosis, and organ atrophy (skin, testes, ovaries, etc).

However, there are differences. Mice seem to age much faster than humans: a 2 year old mouse is equivalent to a 69 year old human (1) and they are pretty old at 24 months of age. Furthermore,  mouse cell biochemical rates are  faster (leading to their incredibly rapid development growth) (8). Those two factors seem to contribute to a much higher death from cancer in mice (9) - when they live long enough. 

What is interesting about aging in both mice and humans is that aging seems to be already pre-programmed into mice and our cells. Assuming the environment is friendly and nourishing, both species will travel inexorably down the path that has been defined for them: towards an aged and frail body, riddled with disease.

Clearly environmental factors plays a role in healthy aging (10, 11). Unfortunately, though, even with optimal environmental conditions, there is still a trajectory moving mice and men (and women) towards an older phenotype.

Is this true for all animals? This brings us to the next article; do all animals age?

Aging is not a foregone conclusion for all species. There are invertebrates (for example, hydra, corals, quohag clams) that live centuries. Even within mammals, some species are much longer lived than others.

In the next article, I will highlight some fascinating facts regarding animals that live far longer than seems logical. And to add an extra wrinkle to this, many of those animals don't exhibit the typical signs of aging, until very late in their lifespan. They seem to live a long, healthy, and young life, and spend very little of that time as an aging creature.