  It is shown that among the R+beta S^{abc}S_{abc} models, only the one with
beta=1/2 has nonvanishing torsion effect in the Robertson--Walker universe
filled with a spin fluid, where S_{abc} denotes torsion. Moreover, the torsion
effect in that model is found to be able to replace the big-bang singularity by
a big bounce. Furthermore, we find that the model can be obtained under a
Kaluza--Klein-like ansatz, by assuming that the gravitational gauge group is
the de Sitter group.
