Given any elliptic curve $E$ over the rationals, we show that 50 % of the quadratic twists of $E$ have $2^{\infty}$-Selmer corank 0 and 50 % have $2^{\infty}$-Selmer corank 1. As a result, we show that Goldfeld's conjecture follows from the Birch and Swinnerton-Dyer conjecture.