Slightly off-topic here, but I love this stuff. One of the blog’s favorite science books of all time is Jonathan Weiner’s Pulitzer-winning The Beak of the Finch (Knopf, 1994), which popularized the notion that beak size among birds (specifically, the finches of the Galápagos) varies from generation to generation based on the size of the seeds (or other foods) that are available. In a geography with a highly variable climate, different seasons can favor different types of vegetation that produces seeds that are more or less difficult to get at with certain configurations of beaks (long and thin vs. short and stubby, etc.). From generation to generation, beak size varies in response to these changes in the available food supply; those birds whose beaks do not allow them to access available food are not able to reproduce while those with optimally sized and shaped beaks will pass there genes along—essentially, this is evolution in more or less real time, and has become pretty much conventional wisdom in evolutionary biology circles. However, via Scientific American, a brace of new studies indicates that the situation is more complex than that: beak size can also be a function of climate. That is, birds’ beaks also regulate temperature and conserve water. In one study:

Typically, birds pant to release excess heat, but this can also lead to water loss. Greenberg hypothesizes that some bird species can use their beaks as a radiator to shed excess heat without losing water—like a jackrabbit's ears. Beneath the skin, a beak has high vascularity and is uninsulated; if the bird's blood is hotter than the surrounding air, the heat will flow from the beak into the surrounding air. Greenberg calculates that by shedding extra heat through its larger beak, the Atlantic song sparrow saves about 8 percent more water than the larger-beaked eastern sparrow. Eight percent may not sound like a lot, but it could enable a bird to continue gathering food, defending its territory or seeking mates on hot days.

In the second study:

the team found that temperature explained over 40 percent of the variation in beak size; in areas with higher maximum temperatures, birds were more likely to have larger beaks—up to a certain point, that is. Past 37 degrees Celsius, beaks began to shrink. To Greenberg and Symonds, this roughly supports a second prediction of the hypothesis: The sparrows have a body temperature of around 41 degrees C, and heat flows to cold. So if the air temperature exceeds 41 degrees C, the larger beak could absorb heat and become a liability.

Peter Grant, one of the scientists who is featured in The Beak of the Finch and did much of the pioneering research on beak morphology and food availability, was complimentary toward the new studies. After all, these new findings do not preclude beak size also being a function of the food that birds can scrounge up. Rather, they just point out that, as with just about any biological trait, a host of different factors can all play a role in how those traits evolve. I had said that this post was slightly off-topic, but as I was rereading the flap copy on my original first edition hardcover of The Beak of the Finch, the last line reads:

Here, brilliantly and lucidly recounted—with (continued on back flap) (continued from front flap) important implications for our own day, when man’s alterations of the environment are speeding the rate of evolutionary changes—is a scientific enterprise in the grand manner, an abstraction made concrete, a theory validated in life. [Emphasis added]

And that flap copy was written in 1994. Today, 18 years later, as climate change is affecting ecosystems practically all over the world, what collection of factors will affect the traits of the next generations of plants and animals? How will things change in the decades to come? How will we change in the decades to come?