Hairy Ardi issue
In the report on Ardi (“Evolution’s bad girl,” SN: 01/16/10, p. 22), the artist’s illustrations show her in fur. The fact that her purported descendants are relatively hairless has been popularized by Desmond Morris (The Naked Ape, 1967) and Elaine Morgan (The Descent of Woman, 1972). What is the paleoanthropologists’ evidence that Ardi had not yet shed her fur coat and gained the advantage of superior heat loss in tireless pursuit of game?
Walter J. Freeman, Berkeley, Calif.

Hairiness made sense for an early hominid species that lived in forests, had infants that could hang on to mothers with grasping toes, and, despite walking upright, couldn’t go anywhere fast in tireless pursuit of anything, says anthropologist and Ardi researcher Owen Lovejoy of Kent State University in Ohio. Long-distance hunting did not emerge as a regular practice until several million years after Ardi’s time and played no major role in hominid hair loss, in Lovejoy’s view. Significant hair loss probably occurred once Homo sapiens developed cultural means for controlling body temperature, such as clothing and water containers, he contends. — Bruce Bower

Midwestern cool-down
The article “Irrigation could be cooling Midwest” (SN: 2/13/10, p. 15) says that the average global temperature rose 0.74 degrees Celsius during the past century and then shows the number of 90 degree-plus [Fahrenheit] days for the past 80 years. Why the difference in time scales? What was the temperature for the past 80 years?
Richard A. Kroc, Batavia, Ill.

The graph of 90 degree-plus days that you refer to shows data only from Chicago. Northern Illinois University scientist David Changnon’s research focused on meteorological data gathered between 1930 and 2009, because the longest set of weather data from a site in the Chicago area comes from a weather station at Midway International Airport, where meteorologists first began collecting data in 1928. For the 80-year period that Changnon studied, global average temperature increased by about 0.65 degrees Celsius, according to data compiled by NASA’s Goddard Institute for Space Studies in New York City.

Information on the temperature rise for the last century was provided in the article solely for the purpose of general context. That figure comes from data compiled by the Intergovernmental Panel on Climate Change. — Sid Perkins