F. Druelle, G. Berillon and P. Aerts; Journal of Zoology, Volume 301, Issue 3, pages 235–247, March 2017
The development toward locomotor autonomy is a long journey for primate (altricial) species. Although the process is multidimensional, the mechanical properties of the changing body are likely to influence the direction and the timing of this journey. Indeed, according to the biomechanical theory, the animal body can be seen as a machine the shape and size of which impact movement via their resistance to linear and angular acceleration. In this context, the mechanical properties, particularly at the level of the legs, are likely to facilitate and/or constraint the learning processes of locomotion.
In order to explore the interactions between the intrinsic body mechanics and the manner in which primates improve their walking gaits, we followed a group of six young baboons living with their mothers and within their social group in captivity. The baboon is an interesting model for our aims because it is described as a committed quadruped and the locomotor development lasts around a year and a half. Therefore, a follow-up of these animals was possible in the context of a doctoral study. We were able to assess the interlimb coordination pattern during quadrupedal walking of the young baboons via the quantification of the temporal aspects of their gaits during their daily activities. We assessed the mechanical properties of their bodies via external measurements and the use of a geometrical model. The natural pendular period of a limb, i.e. the period of oscillation at which exchange between potential and kinetic energy would be maximal and metabolic energy would be minimal, is put forward for representing the intrinsic limb morpho-dynamics.
Our results are of great interest because they demonstrate the presence of an early optimization of the limbs in baboons. Indeed, during development, fore and hind limbs are strongly convergent at the level of their natural pendular period. Interestingly, this affects the coordination pattern but this effect does not interact with age, therefore revealing a parallel factor of the neuromuscular maturation. These limbs’ mechanical properties are likely to be adaptive in facilitating the learning processes toward quadrupedal walking in baboons. Indeed, an early acquisition of locomotor skills in young baboons should favor their survivorship. Female baboons usually resume sexual cycling 12 months after they gave birth involving that at this time their infant must be able to locomote efficiently on the ground in order to keep following their group. Our finding is therefore in line with the specific needs related to the baboons’ socio-ecological niche. These results also question the presence of other body optimizations in young primates according to their species-specific ecological niches.