Smaller May Be Better

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Dr. William V. Raszka, our Associate Editor, offers the following insight into a current topic in the news:

It is mid-winter as I write this and the temperature in northern Vermont is almost 50 degrees. The ski pass I bought last June has been used exactly four times. Our lawn and driveway, rather than lying under inches or feet of snow, are mud. While I have lived through other warm spells and warm winters, I keep thinking that the weather patterns in Vermont have changed a lot in the past 20 years. I keep wondering about other effects of warm weather.

According to an article in The New York Times (Science: February 2, 2012), one possible outcome may be that mammals will become smaller. Scientists studied the fossil record of the Sifrhippus, the first horse, in the Bighorn Basin of Wyoming. The horse roamed the area approximately 56 million years ago and survived the Paleocene-Eocene thermal maximum period: a 175,000-year time period in which ambient temperatures are thought to have risen by 9 to 18 degrees Fahrenheit before dropping at the end. The fossil record of the Sifrhippus is extensive and quite well preserved, showing that over the first 130,000 years of this warming period the horse shrank in size almost 30% (dropping from an average weight of 12 to eight and a half pounds).

During the next 45,000 years, as the temperatures cooled, the average weight shot up and approached 15 pounds. Some scientists theorized that the most likely explanation for the shrinkage was natural selection driven by the warming trend. One hypothesis is that smaller animals do better in warmer climates because it is easier for small animals to shed heat. Other scientists dispute the findings, suggesting that the warming trend and changes in the ecosystem led smaller animals to migrate to different locations. Still, the findings seem to fit with Bergmann’s rule, which holds that mammals of a particular species tend to be smaller in hotter climates. How applicable the findings are to modern mammals is unclear. After all, the changes in the Sifrhippus took place over thousands of years. Still, the study is a reminder how interconnected all living creatures are with nature.

Noted by WVR, MD

*This filler excerpt can be found in the June 2012 Pediatrics print journal p. 1063, or via online here.