In situ observations of the solar wind frequently show the temperature of α particles (fully ionized helium) T_{α} to significantly differ from that of protons (ionized hydrogen) T_{p}. Many heating processes in the plasma act preferentially on α particles, even as collisions among ions act to gradually establish thermal equilibrium. Measurements from the Wind spacecraft's Faraday cups reveal that, at r=1.0 AU from the Sun, the observed values of the α-proton temperature ratio, θ_{αp}≡T_{α}/T_{p}, has a complex, bimodal distribution. This study applied a simple model for the radial evolution of θ_{αp} to these data to compute expected values of θ_{αp} at r=0.1 AU. These inferred θ_{αp} values have no trace of the bimodality seen in the θ_{αp} values measured at r=1.0 AU but are instead consistent with the actions of the known mechanisms for α-particle preferential heating. This result underscores the importance of collisional processes in the dynamics of the solar wind and suggests that similar mechanisms may lead to preferential α-particle heating in both slow and fast wind.