We show that every algorithm for testing $n$-variate Boolean functions monotonicity must have query complexity $\tilde{\Omega}(n^{1/4})$. All previous lower bounds this problem were designed nonadaptive algorithms and, as a result, the best bound general (possibly adaptive) testers was only $\Omega(\log n)$. Combined with of tester Khot, Minzer, and Safra (FOCS 2015), our shows adaptivity can r...