When most creatures speed up from a gentle walk, they eventually slip into a trot, and finally a run or gallop at top speed. But quadrupedal primates never seemed to break into a trot on course for a high-speed gallop. According to Daniel Schmitt and his colleagues from Duke University and the University of Alberta, the animals seemed to switch gear from a walk to a gallop with little or no transition between the two extremes. Curious to know which gaits primates adopt at intermediate speeds, Schmitt and his co-workers put primates, ranging in size from 70 g to 25 kg, through their paces to see which gait the animals selected (p. 2042).

Filming the primates, the team gathered clear evidence that the animals rarely broke into a trot, and almost always preferred to amble' at intermediate speeds. And when the team mathematically modelled the primate's gait, they realised that the ambling gait significantly reduced the amount that the animal's body bounced up and down. Analysing the mathematical model,Schmitt and his colleagues found that the gait that generated the minimum body-bounce in the mathematical model corresponded well with the ambling gait that the animals preferred at intermediate speeds.

Schmitt suggests that primates amble in preference to trotting to retain stability while rushing through trees. Ambling may also be part of a set of basal adaptations associated with the origin of primates 65 million years ago'says Schmitt.

Schmitt, D., Cartmill, M., Griffin, T. M., Hanna, J. B. and Lemelin, P. (
2006
). Adaptive value of ambling gaits in primates and other mammals.
J. Exp. Biol.
209
,
2042
-2049.