Natural selection makes the best mice

Several years ago, I found myself in possession of an abandoned baby deer mouse. She was too little to survive on her own, so when it was clear that no mousey help for her was coming, I took her in as a pet.

Garlic Jack the day I found her, snuggling with a warm water bottle wrapped in a sock

Snuggling and eating some peanut butter cut with cream

Love that warm water bottle!

Like all mice, she grew up quickly. Being a mouse means everything wants to eat you, so you grow up and have lots of babies as quickly as possible in the hopes of leaving some offspring before you are chomped.

It also means not investing much in any one baby, since you have lots. This may be how Garlic Jack ended up alone and crying in my apartment in the first place: if her mother didn’t have the energy to care for her, she would not have hesitated to abandon her. Stressed-out mouse mothers often will even eat their babies, taking that energy back for a less stressful, more promising time.

Garlic Jack as an adult

Mice are extremely social animals, not unlike humans, and do no better than we would in solitary confinement. So when Garlic Jack was big enough to hold her own, I got her some domestic mouse friends, “feeders” from the local pet store.

From the first it was obvious who was the product of stringent natural selection and who had been bred to be snake food. They lumbered; she zoomed.

Aww, leave me alone, guys, I’m trying to run!

I can run the normal way…

…but this is better!

Look, three paws!

Domestic mice are bigger than she is, with proportionally smaller heads, ears, and eyes. Where she is built to survive famine and hear and see predators, they are built to thrive under human care. Since most humans breeding mice intend them as food for other animals, domestic mice have not lost their ancestral ability to produce lots of babies very fast, but they have lost some of their predator-detection abilities (detecting the snake does not help your survival chances when you are locked in its cage), and they have acquired a tolerance for human handling.

You cannot handle Garlic Jack. You cannot catch her: even gravity seems to lose its grip on her occasionally.

No, this photo is not upside-down.

No big deal. Sometimes she does this dozens of times in an hour.

Strangely, even in human care—which the domestic mice are adapted to, and she is not—she has proved hardier than they. Over three years she’s outlived several waves of domestic friends; none of them have come close to matching her longevity. This is probably because domestic mice are inbred, and so suffer from accumulations of recessive mutations that make them less hardy even under the best conditions.

At three years old she is perhaps less shiny than in her youth, but she is still a creature of piercing alertness and pure quicksilver energy. She refuses to run in the wheel properly: instead, she runs until she gets up momentum, then clings while the wheel whirls her ’round and ’round. I don’t know what natural experience this could possibly evoke, but she seems to love it.

Despite their genetic differences, she and the domestic mice get along well.

Clockwise from left: Coffee, Butter Pecan, Oreo, Garlic Jack, Bagel.

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5 thoughts on “Natural selection makes the best mice

    • I’ve been wondering that myself! I’m sure in the wild it’s no more than a year, due to predation, but I don’t know what it is in captivity. Some researchers have captive strains of deer mice for their work, so I’m sure someone knows. I’m hoping it’s well over 3 years.
      And thanks, I’m glad you like the names! The rule is to name them after human-produced food: they’re arguably human-produced, being domestic, and it’s sort of a nod to their escaping “feeder” fates. (Garlic Jack isn’t domestic, but I didn’t know “garlic jack” actually fit that pattern – turns out it’s a kind of cheese – until after I’d named her.)

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