  We study monotonicity and 1-dimensional symmetry for positive solutions with
algebraic growth of the following elliptic system: \[ \begin{cases} -\Delta u =
-u v^2 & \text{in $\R^N$}\\ -\Delta v= -u^2 v & \text{in $\R^N$}, \end{cases}
\] for every dimension $N \ge 2$. In particular, we prove a Gibbons-type
conjecture proposed by H. Berestycki, T. C. Lin, J. Wei and C. Zhao.
