Misfit? Or totally Fit?


The term “fitness” congers images of six-pack abs, yoga poses, and 90’s spandex leotards (for me, anyway).  But those images can be misleading when it comes to understanding evolutionary fitness.

Good “fitness” in evolution means “a good fit.” Organisms that fit well in their environmental niche spend less energy just trying to survive; they have more energy left over for reproduction. So fitness is often measured by the number of offspring produced.

A sloth is well camouflaged with its slo-mo movement. Many predators detect prey by movement (if we stick with the 90’s imagery, remember the T.rex in Jurassic Park “can’t see us if we don’t move”). Low metabolism in sloths means very low food requirements. One study measured sloth metabolic rate at 174 kJ (kilajoules) per day. (1) Just for comparison, an average human requires 6000-7000 kJ per day.

  1. Nagy, KA and GG Montgomery. 1980. Field metabolic rate, water flux, and food consumption in three-toed sloths (Bradypus variegatus). Journal of Mammalogy 61(3)465-472

G’night, Groundhog


It may seem like an odd time for a post about groundhogs (Marmota monax) – a couple months early, right? But I think now is an even better time. Groundhogs (a.k.a. woodchucks or whistle-pigs) are considered one of the few true hibernators of winter.

What about bears? This is where we get into an issue of degrees (pun totally intended). Bears lower their metabolism and body temperature, and by doing so, conserve energy in winter when food supplies dwindle. Normally, bear body temperature is ~98.6⁰ F (37⁰ C), just like humans. In torpor (like a mild hibernation), their body temperatures drop to 86⁰ F (30⁰ C).

The groundhog, in comparison, can lower its body temperature from 99⁰F to 37⁰ F (5⁰ C)! That’s hibernation! It allows the rodent to decrease its energy use to 1% of normal.

Think of torpor and hibernation like changing the temperature settings in your house. In torpor, you drop the settings a couple of degrees while you’re at work. Hibernation is like shutting temps way down, just enough to keep the pipes from freezing, while you head to Florida for a month-long vacation.

Some scientists study how the groundhog accomplishes this marvelous feat. Figuring out those specifics could impact healthcare and space travel for humans.

p.s. Some animals hibernate in the summer, but this is called aestivation (est-eh-VAY-shun).

p.p.s. This watercolor is now available on RedNewtGallery’s Etsy site. (yay!)