This paper is concerned with the asymptotic spreading of a Lotka-Volterra
cooperative system. Utilizing the theory developed by Berestycki et al.
[Asymptotic spreading in heterogeneous diffusive excitable media, J. Funct.
Anal. \textbf{255} (2008), 2146-2189] for nonautonomous scalar equations, the
lower bounds of spreading speeds of unknown functions formulated by a coupled
system are estimated. Our results imply that the asymptotic spreading of one
species can be significantly fastened by introducing a mutual species, which
indicates the role of cooperation described by the coupled nonlinearities.