Did Lucy Walk Too Slow for Her Taller Group Mates?
Did Lucy Walk Too Slow for Her Taller Group Mates?
If you’re on the shorter end of the height spectrum, you know how frustrating it can be to take a stroll with someone who’s tall. At times, you might have to remind your companion to slow down, that your shorter legs can’t keep up. This might have been an even bigger problem for our famous ancestor, Lucy. Within the species Australopithecus afarensis, there was considerable variability in height and limb length, and different members of the species may have had vastly different preferences for walking speeds, new research suggests. How did our ancestors cope with such a dilemma?
The problem really became apparent in 2010 with the discovery of a partial A. afarensis skeleton, nicknamed “Big Man,” in Ethiopia. As his name suggests, the five-foot-tall Big Man was big, at least for an early hominid, and compared to the three-and-a-half-foot-tall Lucy. Big Man’s shin, for instance, was about 50 percent longer than that of Lucy’s—the sort of length difference you see today between a six-year-old child and a six-foot-tall man. But in Lucy and Big Man’s case, both individuals were adults, suggesting there was a large range of heights for A. afarensis. The variation might have been related to sex, with males being significantly taller than females. Or there might have been regional differences in A. afarensis size. Lucy and Big Man were both found in Ethiopia but at different sites.
To understand the walking behavior of Lucy, Big Man and their kind, Patricia Ann Kramer of the University of Washington in Seattle did some experiments with people. In modern humans, the length of the lower leg (or tibia) plays a big role in how much energy a person expends while walking and what his/her preferred speed is. Kramer examined this relationship by measuring the tibia length of 36 children and 16 adults and then placing the volunteers on treadmills to record how much energy they used (measured in terms of oxygen consumption) while walking at different speeds. She discovered that, in general, individuals with longer lower legs have higher “optimal velocities.” That means the speed at which longer-legged people consume the least amount of energy is faster than that of shorter-legged people.